Select your language

Suggested languages for you:
Log In Start studying!
StudySmarter - The all-in-one study app.
4.8 • +11k Ratings
More than 3 Million Downloads
Free
|
|

All-in-one learning app

  • Flashcards
  • NotesNotes
  • ExplanationsExplanations
  • Study Planner
  • Textbook solutions
Start studying

Chemical Kinetics

Save Save
Print Print
Edit Edit
Sign up to use all features for free. Sign up now
Chemical Kinetics

How do you go about increasing the speed of a chemical reaction? One simple way might be by adding more of your reactants into the system. That is exactly what the chemists Peter Waage and Cato Guldberg proposed in 1864, under the name of the law of mass action. This law was the birth of the field of kinetics, the study of the rate (or speed) of reaction.

Chemical kinetics is a branch of physical chemistry that is all about the rate of chemical reactions.

The law of mass action states that the rate of a reaction is proportional to the concentration of the reactants. While this is often true, we now know that there are many other factors that also affect how quickly substances react.

Take the reaction between magnesium and water, for example. Put magnesium in water at room temperature and it will fizz very gently. But combine it with steam and the reaction will be a lot more vigorous. In this article, we’ll look at why that is the case, as well as other questions within the field of kinetics.

  • This article is about chemical kinetics.
  • Firstly, we’ll define rate of reaction.
  • After that we’ll look at the laws of chemical kinetics, including collision theory and factors affecting rate of reaction.
  • We’ll then move on to kinetic graphs such as Maxwell-Boltzmann distributions and enthalpy diagrams.
  • We’ll also look at how you plot rate of reaction graphs. You’ll be able to practice calculating the reaction rate at a particular point in time.
  • After that, we’ll briefly introduce you to rate equations and the Arrhenius equation.
  • Finally, we’ll look at applications of chemical kinetics.

Rate of reaction in chemical kinetics

As we defined above, chemical kinetics is a branch of chemistry that deals with the rate of reactions.

Rate of reaction is a measure of either how quickly reactants are used up, or products are formed, in a chemical reaction. In other words, it is the change in concentration of reactants or products over time.

Some reactions happen extremely quickly. The reactants are used up rapidly and lots of the products are formed in the blink of an eye. They have a fast rate of reaction. But other reactions are slow. For example, the rusting of an iron nail can take years and years. The iron, one of the reactants, is gradually turned into iron oxide, the product. Because the change in the concentrations of reactants and products is gradual, we say that this process has a slow rate of reaction. Rate of reaction is simply a way of measuring how quickly one species turns into another.

Measuring rate of reaction

You can measure rate of reaction in a number of different ways. Any method is valid, so long as you measure the change in amounts of reactants or products. For example, you could:

  • Measure the change in mass of a reaction with gaseous products.
  • Measure the volume of gas given off for a reaction with gaseous products.
  • Measure light passing through the solution for a reaction that produces a cloudy suspension.
  • Measure the change in pH of a solution.

To measure rate of reaction, start your reaction. At regular time intervals, take a measurement as described above and record both the time and the measurement value in a table. Once the reaction is complete, plot a graph with time on the x-axis and your measurement, be it volume of gas or mass of reactants, on the y-axis. Join the points up with a smooth curve. To calculate rate of reaction, you then need to find the gradient of this curve. Don’t worry - we’ll show you how to do this later on.

Units of rate of reaction

The units of rate of reaction vary, depending on what you are measuring. Examples include g s-1, cm3 s-1 or mol dm3 s-1.

Laws of chemical kinetics

Chemical kinetics, and the rate of all reactions, is based on one underlying law: the principle of collision theory. It’s a simple concept, but from it we can derive many of the factors affecting rate of reaction.

First, let’s define collision theory.

Collision theory

Collision theory is an explanation for the rates of many reactions. It proposes two key ideas: particles must collide with the correct orientation, and sufficient energy in order for a reaction to occur.

Reactions can only happen if two particles collide. However, this on its own isn’t enough. Collision theory dictates that in order to react, the particles must also have the correct orientation and sufficient energy. What does this mean?

Let’s use the reaction between chloroethane, and a hydroxide ion, as an example. They can react together to form an alcohol, in an example of what we call Nucleophilic Substitution Reactions. In order for a reaction to occur, the lone pair of electrons on the oxygen atom must collide with the carbon atom in the C-Cl bond. Nothing will happen if, say, the hydrogen atom in the hydroxide ion collides with the other end of the ethane chain! The molecules need to be orientated in just the right way in order for a reaction to occur.

Chemical Kinetics orientation StudySmarterParticles must collide with the correct orientation in order for a reaction to occur. Anna Brewer, StudySmarter Originals

But orientation isn’t the only requirement. Even if the hydroxide ion and the chloroethane molecule collide with the correct orientation, they still might not react. They also need to have enough energy. This energy is known as the activation energy.

Activation energy is the minimum amount of energy needed to start a chemical reaction. It takes the symbol Ea.

Reactions need some initial energy in order to break the bonds in the reactants. Breaking bonds is an endothermic process, meaning that it requires energy. Energy is then released when bonds form to make the products.

To summarise, in order for a reaction to take place, two particles must first collide. They must also have the correct orientation. Finally, they need enough energy. If, and only if, they meet all these criteria, will a reaction occur. We call a collision that results in a reaction a successful collision.

Factors affecting rate of reaction

Collision theory tells us that particles need to collide with the correct orientation and enough energy in order for a reaction to take place. To increase the rate of reaction, we must therefore change any of the following three things:

  • The particles’ orientations.
  • The particles’ energy.
  • The frequency of the particles’ collisions.

We can do this in a number of different ways.

Surface area

Increasing the surface area of a solid increases the rate of reaction. This is because there are more particles exposed on the surface of the solid. Liquid, aqueous or gaseous particles can collide with these exposed solid particles, potentially causing a reaction. So, increasing the surface area increases the frequency of collisions.

Concentration

Increasing the concentration of a solution increases the rate of reaction. This is because there is a greater number of solute particles in a given volume, which increases the frequency of collisions.

Pressure

Increasing the pressure of a gas increases the rate of reaction. Similar to increasing concentration, this increases the number of particles in a given volume and so increases the frequency of collisions.

Temperature

Increasing the temperature of a reaction increases the rate of reaction. This is for two reasons. Heating the particles supplies them with more energy. Some of this is turned into kinetic energy, meaning the particles move faster. This means that they collide more frequently. But more importantly, having more energy means that the particles are more likely to meet the activation energy when they do collide. Heating a reaction not only increases the frequency of collisions, but also the frequency of successful collisions.

Catalysts

Adding a catalyst increases the rate of reaction. This is because catalysts provide an alternate reaction pathway with a lower activation energy. Although they don’t change the frequency of collisions, catalysts increase the proportion of successful collisions.

Some catalysts also hold the particles in place, positioning them in just the right way for passing particles to collide with. This ensures that they have the correct orientation.

Chemical kinetic graphs

Now that we know what kinetics is, and have learnt about factors affecting rate of reaction, we can turn our attention to kinetic graphs. There are a few different types of graphs you might come across in kinetics. We’re going to look at three in particular:

  • Enthalpy diagrams
  • Maxwell-Boltzmann distributions
  • Rate of reaction graph

Enthalpy diagrams

An enthalpy diagram is a graph that shows certain characteristics of a reaction, such as the reactants’ starting energy, the products’ final energy, and the activation energy. Enthalpy diagrams are also known as energy profiles.

Look at the graph below. It is a great example of an enthalpy diagram for the formation of sodium chloride. In this reaction, sodium reacts with chlorine gas to produce the salt sodium chloride.

Chemical Kinetics enthalpy diagram StudySmarterAn enthalpy diagram for sodium chloride. Anna Brewer, StudySmarter Originals

The graph tells us a few things.

  • The products have less energy than the reactants. This makes the reaction an exothermic reaction - overall, energy is released.
  • There is a peak in the curve between the reactants and the products. This is the activation energy we talked about earlier. To start a reaction, particles must collide with enough energy to get over this energy barrier.

Let’s now look at an enthalpy diagram for an endothermic reaction. One such example is the reaction between sodium carbonate and ethanoic acid.

Chemical Kinetics enthalpy diagram StudySmarterAn enthalpy diagram for the formation of sodium ethanoate. Anna Brewer, StudySmarter Originals

Note the following:

  • The products are higher up on the graph than the reactants. This means that they have more energy - overall the reaction is endothermic.
  • There is still a peak in the curve representing activation energy.

Let’s now go back to one of the factors affecting the rate of reaction: the presence of a catalyst. Catalysts reduce the activation energy requirements of a reaction. How do you think they change the reaction’s enthalpy diagram?

Well, the peak will be lower. Remember that the peak represents the activation energy. So, if the activation energy is lower, the height of the peak will decrease too. You can see this in the graph below.

Chemical Kinetics enthalpy diagram catalyst StudySmarter

An enthalpy diagram for a reaction with and without a catalyst. Anna Brewer, StudySmarter Originals

The highest point of the graph at the top of the peak is known as the transition phase. At this point, all the bonds within the reactants have broken but new bonds haven't quite formed, and the molecules and atoms exist as unstable intermediates. Breaking bonds is an endothermic process, meaning that it requires energy, and this is what the activation energy is used for.

Head over to Enthalpy Changes to explore enthalpy diagrams in more detail.

Maxwell-Boltzmann distributions

Another type of graph found in kinetics is the Maxwell-Boltzmann distribution.

The Maxwell-Boltzmann distribution is a probability function that shows the distribution of energy amongst the particles of an ideal gas.

Different particles within a gas have different energy levels. Some have a lot of energy, while others only have only a little. Most have a medium amount of energy. We can plot these energy levels on a Maxwell-Boltzmann distribution, a graph showing the number of particles on the y-axis and energy on the x-axis. We get something looking a little like the following. You’ll notice that three points have been marked: the most probable energy, the average energy and the activation energy.

Chemical Kinetics Maxwell-Boltzmann distribution StudySmarterThe Maxwell-Boltzmann distribution. Anna Brewer, StudySmarter Originals

What does this tell us?

  • The area under the graph represents the total number of particles in the system.
  • The most probable energy is the mode energy value. It is the one particular energy value that the greatest number of particles have.
  • The average energy is the median energy value. Exactly half of the particles have more energy than this and exactly half of the particles have less energy than this.
  • The area under the graph to the right of the activation energy represents the number of molecules that meet or exceed the activation energy. The greater this area, the greater the proportion of successful collisions.

You can explore these types of graphs further in Maxwell-Boltzmann Distribution. You’ll also be able to see how factors like temperature and the presence of a catalyst influence the distribution.

Rate of reaction graphs

Earlier in the article, we explored how you measure the rate of reaction. You do this by measuring how the amount of reactants or products changes over time. Now we are going to focus on graphing this information.

Let’s go back to our example of sodium carbonate and ethanoic acid. This produces the gas carbon dioxide, . We can therefore measure the rate of reaction by measuring the volume of carbon dioxide given off. To do this, we use a gas syringe, taking readings at regular time intervals and recording them in a table. We can then plot these points on a graph with time on the x-axis and volume on the y-axis. Ideally, your data points should show a smooth curve.

Chemical Kinetics rate of reaction graph StudySmarterA graph showing volume of gas given off against time. This is a measure of rate of reaction. Anna Brewer, StudySmarter Originals

Note the following:

  • The curve starts off steep. This means that lots of the product is produced very quickly and so the rate of reaction is initially fast.
  • The curve gradually levels out. This means that the product is produced less quickly and so the rate of reaction is slower.
  • The curve eventually levels out completely. At this point, no more product is produced - the reaction is over. Here, that happens at 80 seconds.

Overall rate of reaction

Remember, rate of reaction is a measure of how quickly reactants are used up or products are formed in a chemical reaction. Here, we measured the volume of a product given off, . To calculate the overall rate of reaction, we divide the change in volume of by the time taken for the reaction to finish. Here, the reaction stops at 80 seconds - after that, no more is produced.

Chemical Kinetics rate of reaction calculation StudySmarterCalculating overall rate of reaction. Anna Brewer, StudySmarter Originals

The overall rate of reaction is therefore

To find the units of rate of reaction, look at the units of the two variables you are measuring. Here, we are measuring volume in cm3 and time in seconds, s. The equation for rate of reaction is volume ÷ time. If we substitute the units into this equation, we get cm3 ÷ s = cm3 s-1.

Instantaneous rate of reaction

Sometimes you might not want to find the overall rate of reaction, but instead calculate the rate at a particular point in time. To do this, you draw a tangent to the curve at the required time and calculate its gradient.

Let’s say you want to find the rate of reaction at 10 seconds.

  1. First, draw a tangent to the curve at 10 seconds. This is a straight line that just touches the curve at the 10 second mark.
  2. Next, mark any two points on the tangent. Here we’ve chosen the points where t (time) = 0 and t = 30.
  3. Calculate the change in height of the tangent between these two points. In our case, height represents volume. You do this by subtracting the volume at t = 0 from the volume at t = 30, using values taken from the tangent, not the curve itself. Here, .
  4. Calculate the change in width of the graph between these two points. Here, .
  5. Find the gradient of the tangent by dividing the change in height by the change in width. Here, .

Here’s a diagram of the calculation to help you understand the process.

Chemical Kinetics rate of reaction calculation StudySmarterCalculating instantaneous rate of reaction. Anna Brewer, StudySmarter Originals

Chemical kinetics equations

We’ll now turn our attention to equations in chemical kinetics. These include:

  • Differential equations
  • Rate equations
  • The Arrhenius equation

Differential equations and rate equations

Differential equations are equations containing a variable and one or more of their derivatives.

Take the reactant A. We can represent its concentration using [A]. In mathematical terms, its change in concentration is the derivative of [A]: . But you’ll remember that rate of reaction is just the change in amount of reactants or products. Therefore, is simply a way of representing rate of reaction.

In chemical kinetics, we use differential equations to show how the rate of reaction, , depends on the concentration of A, [A], at a particular instant. One example of a differential equation that you do have to know is the rate equation.

The rate equation of a chemical reaction is an equation that links the rate of reaction to the concentrations of species involved in the reaction.

We explored earlier how concentration affects the rate of a reaction. However, this effect isn’t always linear. Sometimes changing the concentration of a particular product has a small effect on the rate of a reaction. Sometimes it has a large effect, and sometimes it has no effect whatsoever. The rate equation links the concentrations of reactants with the rate of reaction using powers, called orders, and a rate constant, k. It typically takes the following form:

Note the following:

  • k is the rate constant, a value that varies for each reaction.
  • [A] represents the concentration of A.
  • x represents the order of the reaction in respect to A.
  • x + y equals the total order of the reaction.

Rate equations is a weighty topic. You’ll learn more about it in Rate Equations.

The Arrhenius equation

We know that changing the concentration of some of the species involved in a reaction can change the rate of reaction. But how about the other factors that affect rate of reaction, such as temperature? These are all cleverly combined into the rate constant, k. However, k is only constant if you keep the temperature and catalyst the same. This is shown in the Arrhenius equation, which links k to several other factors.

The Arrhenius equation is an equation that provides a relationship between the rate constant, the absolute temperature, activation energy, and the pre-exponential factor.

Here’s what the Arrhenius equation looks like:

In this equation:

  • k is the rate constant.
  • A is the pre-exponential factor.
  • e is Euler's number.
  • Ea is the activation energy of the reaction you are studying.
  • R is the gas constant, which you’ll also come across in the ideal gas law.
  • T is the temperature.

Overall, the expression provides a rough approximation of how many particles within a gas meet the reaction’s activation energy at a certain temperature. (See Ideal Gas Law for more on this topic.)

Using this equation, we can clearly see how changing some of the conditions changes the rate of reaction. For example, increasing the temperature increases the value of , the number of particles that meet or exceed the activation energy of the reaction. This in turn makes k larger. Rate of reaction depends on k, so overall, the rate of reaction increases.

This is another heavy topic, and this article is only an introduction to the wonders of the Arrhenius equation. For a more detailed explanation, check out Arrhenius Equation.

Applications of chemical kinetics

You can imagine that controlling the rate of a reaction has many different uses. For example, you might want to slow down the decay of a product or increase the rate of an industrial reaction. Chemical kinetics therefore has lots of applications. These include:

  • Storage of drugs and pharmaceuticals to increase their shelf life.
  • Adding preservatives to food to prevent it from going bad.
  • Choosing the best catalyst for industrial processes.
  • Deciding on the optimal temperature for baking biscuits and cakes.
  • Radiocarbon dating.

Chemical Kinetics - Key takeaways

  • Chemical kinetics is a branch of physical chemistry that is all about the rate of chemical reactions.
  • Rate of reaction is a measure of either how quickly reactants are used up, or products are formed, in a chemical reaction. In other words, it is the change in concentration of reactants or products over time.
  • Chemical kinetics is based on collision theory. Collision theory states that particles need to collide with the correct orientation and sufficient energy in order to react.
  • Factors affecting rate of reaction include temperature, pressure, concentration, surface area, and the presence of a catalyst.
  • An enthalpy diagram is a graph that shows certain characteristics of a reaction, such as the reactants’ starting energy, the products’ final energy, and the activation energy.
  • The Maxwell-Boltzmann distribution is a probability function that shows the distribution of energy amongst the particles of an ideal gas.
  • To calculate rate of reaction, you plot a graph of change in amount of either product or reactant against time, and calculate the gradient of the curve.
  • The rate equation of a chemical reaction is an equation that links the rate of reaction to the concentrations of species involved in the reaction.
  • The Arrhenius equation is an equation that provides a relationship between the rate constant, the absolute temperature, activation energy, and the pre-exponential factor.
  • Applications of chemical kinetics include preservatives for food and medicine and using catalysts to speed up industrial reactions.

Frequently Asked Questions about Chemical Kinetics

Applications of chemical kinetics include storing pharmaceuticals to increase their shelf life, adding preservatives to food to prevent it going bad, using catalysts to speed up chemical reactions, and radiocarbon dating.

Collision theory is an explanation for the rates of many reactions. It proposes two key ideas: particles must collide with the correct orientation and sufficient energy in order for a reaction to occur.


To find the order of reaction in chemical kinetics, you need to find the order of all the different species present in the rate equation. You can do this by looking at data showing the rate of reaction for different concentrations of the various species. For example, if you double the concentration of A whilst keeping all other variables the same, and the rate of reaction doubles as a result, you know that the reaction rate is first order with respect to A. If you double the concentration of A and the rate of reaction increases fourfold, you know the reaction rate is second order with respect to A. Check out the article “Determining Rate Equation” for more.

Rate of reaction is the change in concentration of reactants or products over time.

This depends on what you want to calculate. For example, you could use the Arrhenius equation to see how the rate constant k depends on the temperature of a reaction. You could also use the rate equation to see how the rate of reaction varies according to the concentrations of different species. More simply, you could calculate rate of reaction by measuring the change in concentration of a product or reactant and dividing it by the time taken.


Final Chemical Kinetics Quiz

Question

What is chemical kinetics?

Show answer

Answer

Chemical kinetics is a branch of chemistry that seeks to understand how the rates of chemical reactions can be influenced.

Show question

Question

The reactivity of chemical agents is the only factor when determining the speed of a chemical reaction. True or false?


Show answer

Answer

False. There are other experimental factors to consider when trying to determine how fast a reaction will occur.

Show question

Question

What is the study of the rates of chemical reactions called?

Show answer

Answer

Kinetics, or Chemical Kinetics, or Reaction Kinetics.  

Show question

Question

What is collision theory?

Show answer

Answer

Collision theory states that the rate of a chemical reaction is proportional to the number of collisions between reactant molecules.


Show question

Question

 What is an effective collision? 


Show answer

Answer

An effective collision is a collision that results in a chemical reaction.

Show question

Question

What is the activation energy?

Show answer

Answer

This is the minimum kinetic energy required by a reactant molecule for a reaction to occur.

Show question

Question

What is the Maxwell-Boltzmann Distribution? 



Show answer

Answer

The Maxwell–Boltzmann distribution is a probability distribution that shows how the speeds of molecules are distributed for an ideal gas.


Show question

Question

Temperature can influence the shape of the Maxwell-Boltzmann curve. True or false?


Show answer

Answer

True. Variations in temperature can change the shape of a Maxwell-Boltzmann distribution curve. Since molecules have less kinetic energy at lower temperatures, the speeds of the molecules are lower and the distribution has a smaller range. As the temperature of the molecules increases, the distribution flattens out, and the speeds of the molecules are greater. 


Show question

Question

What is a kinetic factor? 


Show answer

Answer

A kinetic factor is a parameter which modifies the temporal evolution of a chemical system, by speeding up or slowing down a chemical reaction. 


Show question

Question

What variables can be manipulated in order to speed up reactions?

Show answer

Answer

There are a number of experimental variables that influence the rate of a reaction, such as temperature, pressure, concentration and the use of catalysts. 


Show question

Question

What is collision theory?

Show answer

Answer

For a reaction to occur, the reactant particles, atoms or molecules, must collide and interact with each other in some way: this is collision theory. Collision theory states that the rate of a chemical reaction is proportional to the number of collisions between reactant molecules. The more often reactant molecules collide, the more often they react with one another, and the faster the reaction is.


Show question

Question

What is an effective collision?

Show answer

Answer

Only a small fraction of collisions result in a chemical reaction: these are called effective collisions. Inversely, ineffective collisions do not result in a chemical reaction. 


Show question

Question

How does temperature affect a chemical reaction?

Show answer

Answer

At lower temperatures molecules have less kinetic energy. As the temperature of the molecules increases, so does their kinetic energy, meaning the molecules are moving faster. A slight increase in temperature causes a large increase in the number of molecules with kinetic energy greater than the activation energy, meaning that the rate of reaction increases. 


Show question

Question

What is an exothermic reaction?

Show answer

Answer

When energy is transferred out to the surroundings, this is called an exothermic reaction, and the temperature of the surroundings increases. The energy level decreases in an exothermic reaction. This is because heat energy is given out to the surroundings. Because of this, a reaction is also said to be exothermic when the energy of the product(s) is less than that of the reactants.


Show question

Question

What is an endothermic reaction?

Show answer

Answer

When energy is taken in from the surroundings, this is called an endothermic reaction and the temperature of the surroundings decreases. The energy level increases in an endothermic reaction. This is because heat energy is taken in from the surroundings. Because of this, a reaction is also said to be endothermic when the energy of the product(s) is greater than that of the reactants. 


Show question

Question

What is enthalpy?  

Show answer

Answer

Enthalpy is a measure of the amount of heat absorbed or released during a chemical reaction. It is calculated by subtracting the energy of the reactants from the energy of the products. 


Show question

Question

What is a catalyst ?

Show answer

Answer

Catalysis is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst. Catalysts are not consumed in the reaction and remain unchanged after it.


Show question

Question

How does a catalyst lower the activation energy of a reaction? 


Show answer

Answer

A catalyst can lower the activation energy for a reaction by:


  • Providing a surface for reactions to take place on. Reactant molecules are then oriented at a favourable angle for collisions to occur, increasing the likelihood of successful collisions, thus speeding up the reaction. 
  • Reacting with one or more reactants to form intermediates that require lower energy to form the final reaction product, in the process regenerating the catalyst, and increasing the rate of reaction. 


Show question

Question

What is necessary for a chemical reaction to occur?

Show answer

Answer

In order for a chemical reaction to occur, the reactant molecules must collide. The more often they collide, the quicker the reaction will be. This is also known as collision theory.

Show question

Question

What is an effective collision? 


Show answer

Answer

An effective collision is a collision which results in a chemical reaction. This means that not all collisions participate in the reaction. This is because a collision is only effective if the particles collide with sufficient energy. 


Show question

Question

What is the activation energy?

Show answer

Answer

The activation energy is the minimum kinetic energy required for a reaction to occur. It’s also the energy required to overcome the repulsive forces caused by the outer electrons of the reactant molecules as they collide, enabling the pre-existing bonds between atoms to be broken, and new ones formed, resulting in the products of the reaction.

Show question

Question

How can you increase the rate of a reaction ?

Show answer

Answer

There are many ways of increasing the rate of a chemical reaction. First of all, lowering the activation energy means more reactants are capable of colliding effectively. Second, by altering experimental conditions, we can increase the frequency or the number of collisions, meaning that we can increase the amount of successful collisions and thus speed up the reaction. Both of these methods are achieved thanks to kinetic factors.

Show question

Question

What is a kinetic factor? 


Show answer

Answer

A kinetic factor is a parameter which can impact the rate of a reaction.

Show question

Question

Name a kinetic factor that increases the proportion or frequency of collisions. Explain how it works.

Show answer

Answer

Temperature is a kinetic factor that increases the number of collisions, and thus successful collisions. This is because when the temperature of the reaction medium increases: 

  • the agitation of the reactant molecules is stronger (they are moving around a lot more) which increases the number of collisions.
  • the average kinetic energy of the reactants increases, meaning more particles having kinetic energy equal to or greater than the required activation energy. This increases the likelihood of a collision being an effective collision. 


Concentration is a kinetic factor that increases the frequency of collisions and thus successful collisions. This is because increasing the concentration of the reactant brings about more collisions, since there are more particles in a given volume to collide with, and hence more successful collisions.


Pressure is a kinetic factor that increases the number of collisions and thus successful collisions. This is because if the pressure of gaseous reactants is increased, there are more reactant particles for a given volume. There will be more collisions and so the reaction rate is increased.


Agitation is a kinetic factor that increases the frequency of collisions and thus successful collisions. This is because agitation helps improve contact between reactant particles by mixing them together better, thus increasing the frequency of collisions. 


The surface area to volume ratio is a kinetic factor that increases the frequency of collisions and thus successful collisions. This is because when a solid reagent is broken up, its contact surface with the surrounding medium is increased. Collisions are therefore more likely to occur and the duration of the reaction is reduced.

Show question

Question

What is the kinetic factor which lowers the activation energy?

Show answer

Answer

The kinetic factor which enables chemists to lower the activation energy is catalysis.

Show question

Question

What is chemical kinetics?

Show answer

Answer

Chemical kinetics is a branch of physical chemistry that is all about the rate of chemical reactions.


Show question

Question

How does a catalyst affect the rate of reaction? 


Show answer

Answer

A catalyst increases reaction rates by lowering the activation energy so that a greater proportion of the particles have enough energy to react. A catalyst can lower the activation energy for a reaction by:

  • providing a surface for reactions to take place on and orienting reactants at a favourable angle for collisions to occur, increasing the likelihood of successful collisions.
  • reacting with one or more reactants to form intermediates that require lower energy to form the final reaction product.


Show question

Question

What are enzymes?

Show answer

Answer

Enzymes are proteins that act as biological catalysts. 


Show question

Question

What is the 'lock and key' model?

Show answer

Answer

The 'lock and key' model describes the specificity of enzymes, whose active site and substrate are complementary to each other in shape. Enzymes are in fact substrate-specific.

Show question

Question

Molecules always react when they collide. True or false? 

Show answer

Answer

False

Show question

Question

What are the two main principles of collision theory?

Show answer

Answer

Molecules must collide with the correct orientation and enough energy for a reaction to occur.

Show question

Question

Exothermic reactions have no activation energy. True or false?

Show answer

Answer

False

Show question

Question

What factors affect the rate of reaction?

Show answer

Answer

  • Pressure
  • Concentration
  • Temperature
  • Surface area
  • Catalysts

Show question

Question

Give three ways of measuring the rate of a reaction.

Show answer

Answer

Volume of gas given off, decrease in mass, change in pH.

Show question

Question

What are the two principles of collision theory?


Show answer

Answer

Particles must collide with the correct orientation and sufficient energy in order for a reaction to occur.

Show question

Question

True or false? Exothermic reactions don’t require any activation energy.


Show answer

Answer

False. All reactions require activation energy to break the bonds between the reactants.

Show question

Question

What is activation energy?

Show answer

Answer

Activation energy is the minimum amount of energy needed to start a chemical reaction.

Show question

Question

A collision that results in a reaction is known as a ________.


Show answer

Answer

Succesful collision

Show question

Question

 Give three factors that affect rate of reaction.


Show answer

Answer

Temperature, pressure, concentration, surface area, the presence of a catalyst.

Show question

Question

Increasing the temperature of a reaction increases the particles’ elastic potential energy. True or false?

Show answer

Answer

False. It increases their kinetic energy.

Show question

Question

Catalysts increase the frequency of collisions. True or false? 


Show answer

Answer

False. Catalysts increase the frequency of successful collisions.

Show question

Question

In a Maxwell-Boltzmann distribution, exactly half of the particles have more energy than _____.


Show answer

Answer

The activation energy

Show question

Question

How do you calculate rate of reaction?


Show answer

Answer

Divide the change in concentration of reactants or products by the time taken. You do this by drawing a tangent to the curve at a particular point and calculating its gradient.

Show question

Question

In graphs showing rate of reaction:

Show answer

Answer

The curve starts off steep and levels out.

Show question

Question

The concentrations of all of the reactants affect the rate of reaction. True or false?


Show answer

Answer

False. The concentrations of some reactants don’t affect the rate of reaction.

Show question

Question

True or false? Species that aren’t part of the overall reaction equation can feature in the rate equation.


Show answer

Answer

True. Catalysts can appear in the rate equation.

Show question

Question

Give three applications of chemical kinetics.


Show answer

Answer

Drug storage, food preservatives, radiocarbon dating, speeding up industrial processes.

Show question

Question

What is a Maxwell-Boltzmann distribution?

Show answer

Answer

A probability function that shows the distribution of energy amongst the particles of an ideal gas.

Show question

Question

What is on the y-axis on a Maxwell-Boltzmann distribution graph?

Show answer

Answer

Number of particles

Show question

Question

What is on the x-axis on a Maxwell-Boltzmann distribution graph?


Show answer

Answer

Energy

Show question

60%

of the users don't pass the Chemical Kinetics quiz! Will you pass the quiz?

Start Quiz

Discover the right content for your subjects

No need to cheat if you have everything you need to succeed! Packed into one app!

Study Plan

Be perfectly prepared on time with an individual plan.

Quizzes

Test your knowledge with gamified quizzes.

Flashcards

Create and find flashcards in record time.

Notes

Create beautiful notes faster than ever before.

Study Sets

Have all your study materials in one place.

Documents

Upload unlimited documents and save them online.

Study Analytics

Identify your study strength and weaknesses.

Weekly Goals

Set individual study goals and earn points reaching them.

Smart Reminders

Stop procrastinating with our study reminders.

Rewards

Earn points, unlock badges and level up while studying.

Magic Marker

Create flashcards in notes completely automatically.

Smart Formatting

Create the most beautiful study materials using our templates.

Just Signed up?

Yes
No, I'll do it now

Sign up to highlight and take notes. It’s 100% free.