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Chemical Reactions

A chemical reaction is a process that results in the interconversion of chemical species. In simpler terms, chemical reactions consist of making and/or breaking chemical bonds to form new products.

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Chemical Reactions

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A chemical reaction is a process that results in the interconversion of chemical species. In simpler terms, chemical reactions consist of making and/or breaking chemical bonds to form new products.

Have you ever tried to make soap at home? The art of soap-making is a type of chemical reaction! First, look at the structure of a soap molecule.

Chemical Reactions Structure of Soap StudySmarterFigure 1. Soap molecule structure

Soap is a type of salt made up of fatty acids. The structure of soap consists of a nonpolar hydrocarbon chain containing a carboxylic acid group. The carboxylic acid group forms an ionic bond with a sodium or potassium ion. So, soap has a hydrophobic end that does not dissolve in water (hydrocarbon chain) and a hydrophilic end (ionic salt). When soap comes into contact with grease and water, the hydrophobic end of the soap interacts with the nonpolar molecules of grease and suspends the grease/oil, allowing it to be washed away by water!

Soap forms by the reaction between the triglycerides in fat/oil and an alkali such as aqueous sodium hydroxide or potassium hydroxide.

The chemical reaction for the making of soap is:

Chemical Reactions saponification chemical process StudySmarterFigure 2. The saponification process

  • First, we will discuss chemical reactions and how to balance them.
  • Then, we will look at the different Types of Chemical Reactions and give some examples.

Chemical Reaction Definition


During a chemical reaction, the atoms of the reactants rearrange themselves, forming new bonds and breaking existing ones to create one or more different substances, known as products.

A chemical reaction is a process that results in the conversion of one or more chemical substances into one or more different substances.

When this happens, we can see changes in colour, gas formation, temperature changes, or even the formation of a precipitate. Or, in some cases, the result looks the same as before.

Chemists use chemical equations to show how what happens to the reactants and products involved in a chemical reaction.

  • Reactants are substances that react together to form products.
  • Products are the new substances formed after the chemical reaction takes place.

Chemical Reaction Balance

A very important skill to have when it comes to chemical reactions is the ability to balance chemical equations.

A chemical equation is balanced when the number of atoms is the same on both sides.

To balance chemical equations, there are some steps we need to follow. As an example, take a look at the chemical equation below: $$ \text{K + H}_{2}\text{O} \to \text{KOH + H}_{2} $$

Step 1: Count the number of atoms present on each side of the chemical equation.

First, we need to count the number of atoms for each type of atom present in the reactant and on the product side. To find out the number of atoms for each type, we can multiply the coefficient (which, in this case, is 1) by the number on the subscript.

To make it easier to remember, we can make a simple table below the chemical equation.

Chemical reactions Counting the numbers of atoms presents on each side of the equation Chemical reaction balance StudySmarterFigure 4. Counting the number of atoms present on each side of the equation

If the number of atoms on each side is the same, then it means that your equation is already balanced. Now, if the number of atoms on each side is different, then you need to go to step two.

Step 2: Determine how many atoms you must add in order to balance the chemical equation.

In order to balance this chemical equation, we have to look for multiples of the coefficient. In this example, the coefficients are 1.

The only way to get the same amount of H atoms on both sides you be to add a coefficient of 2 to the H2O molecules, and a coefficient of 2 to the KOH molecules. This way, we would get 4 H atoms on each side.

However, this would also change the number of K atoms on the product side, and the number of oxygen atoms on both sides. To overcome this, we can add a coefficient of 2 to the K on the reactant side. Now, the reaction should be balanced!

Chemical reactions Adding coefficients to balance a chemical equation Chemical reaction balance StudySmarterFigure 5. Adding coefficients to balance a chemical equation

Types of Chemical Reactions

There are five basic Types of Chemical Reactions:

  • Combination or synthesis reactions
  • Decomposition reactions
  • Combustion reactions
  • Single-replacement reactions
  • Double-replacement reactions

Replacement reactions are also called "Displacement Reactions". Neutralization reactions are an example of replacement reactions. Synthesis and single-replacement reactions can be Redox Reactions, which are chemical reactions where electrons are transferred from one species to another.

Synthesis Reactions

Synthesis reactions are reactions in which two or more substances combine to form a new substance. The general formula for synthesis reactions is: \( A + B \to C \).

For example, the formation of hydrogen bromide (HBr) is the result of a Synthesis Reaction between hydrogen and bromine.

$$ H_{2}\text{ (g)} \text{ }+ \text{ }Br_{2} \text{ (l)}\to 2\text{ }HBr \text{ (g)} $$

Oxidation-Reduction (redox) Reactions

In Redox Reactions, electrons are transferred from one species (oxidized) to another species (reduced). A change in oxidation state indicates that a Redox reaction has taken place.

  • Oxidation is the loss of electrons
  • Reduction is the gain of electrons

For example, the reaction between zinc (Zn) and manganese oxide (MnO2) is a type of oxidation-reduction reaction.

$$ Zn\text{ }( s)\text{ + }2\text{ }MnO_{2}\text{ }(s)\text{ }\to \text{ }ZnO \text{ }(s)\text{ + }Mn_{2}O_{3}\text{ }(s) $$

For an in-depth explanation of oxidation-reduction chemical reactions, check out "Redox Reactions"!

Decomposition Reactions

Next, we have decomposition reactions. Decomposition reactions are chemical reactions in which one substance gets converted into 2 or more substances, and the general formula for this is: \( AB \to A + B \).

The decomposition of calcium carbonate (CaCO3) into calcium oxide (CaO) and Carbon dioxide (CO2) is an example of a Decomposition Reaction.

$$ CaCO_{3}\text{ } (s)\to \text{ } CaO \text{ (s)} \text{ + } CO_{2} \text{ (g)} $$

Combustion Reactions

Combustion reactions are reactions involving a hydrocarbon reacting with oxygen (O2) to produce Carbon dioxide (CO2) and water (H2O). These reactions give out energy as heat and light.

A common combustion reaction is the reaction between the hydrocarbon methane (CH4) and oxygen (O2).

$$ CH_{4}\text{ }(g) + O_{2}\text{ } (g) \text{ }\to\text{ } CO_{2} \text{ }(g)\text{ }+\text{ }H_{2}O \text{ }(g) $$

Single Replacement Reactions

Single replacement reactions occur when one element in a compound is replaced by another element. The general formula for single displacement reactions is: \( \color{Teal} A \color{orchid} B +\color{Blue} C \color{black} \to \color{Teal} A \color{black} + \color{orchid} B \color{Blue}C \)

In single replacement reactions, the element that tends to form cations will replace the cation in a compound. Similarly, the element that tend to form anions will replace the anion in a compound.

For example, in a reaction between zinc chloride (ZnCl2) and copper (Cu), copper replaces the Zn to form cooper chloride (CuCl2).

$$ ZnCl_{2}\text{ } (s)\text{ + } Cu \text{ } (s) \text{ } \to \text{ }CuCl_{2}\text{ } (s)\text{ } + \text{ } Zn\text{ } (s) $$

Double Replacement Reactions

Double replacement reactions occur when two compounds reacts in aqueous solutions, causing the cations and anions of the two reactants to "trade partners or switch places" to form two new compounds. The general formula is this case is: \( \color{Teal} A\color{Orchid} B\color{black}\text{ } + \text{ }\color{Blue} C\color{Orange} D\color{black} \text{ }\to \text{ }\color{Teal} A\color{Orange} D\color{black}\text{ } + \text{ }\color{Orchid} B\color{Blue} C \).

For example, the reaction between mercury (II) nitrate and diammonium sulfide in aqueous solutions to yield mercuric sulfide and ammonium nitrate is a type of double replacement reaction.

$$ Hg(NO_{3})_{2} \text{ }(aq)\text{ + }(NH_{4})_{2}S\text{ }(aq) \text{ }\to HgS \text{ }(s) \text{ + } 2NH_{4}NO_{3} \text{ } (aq) $$

Neutralization Reactions

Neutralization reactions are a special type of double replacement reactions in which one reactant is an acid and the other is a base, giving salt and water as products. The equation below is an example of a neutralization reaction.

$$ HCl \text{ (acid) + }LiOH\text{ (base) } \to LiCl \text{ (salt)}+ H_{2}O \text{ (water)} $$

Chemical Reaction of Photosynthesis

Now that you are aware of the different types of chemical reactions that can occur around you, let's take a look at the chemical reaction happens in photosynthesis.

Photosynthesis is the process of using solar energy to convert carbon dioxide (CO2) and H2O into carbohydrates (glucose) and oxygen (O2).

The process and chemical reaction of photosynthesis is shown in the figure below.

Chemical Reaction Examples

Lastly, let's look at some examples involving chemical reactions. Let's start with the following reaction: \( \text{Zn + AgNO}_{3}\to \text{Ag + Zn(NO}_{3}\text{)}_{2} \).

Can you guess which type of chemical reaction it is? Well, if you guessed that it is a Decomposition Reaction, you are right!

Now, let's amplify the difficulty a bit and solve a problem similar to what you might see in your exam.

What type of chemical reaction occurs between CoCl3 and Ba(OH)2?

$$ 2\text{ }COCl_{3}\text{ + } 3\text{ }Ba(OH)_{2}\text{ }\to\text{ }3\text{ }BaCl_{2} \text{ + }2\text{ }Co(OH)_{3} $$

  1. Combustion
  2. Single replacement
  3. Double replacement
  4. Decomposition
  5. Synthesis

The chemical reaction above is an example of a double replacement reaction because cations and anions of the two reactants "switched places" to form two new compounds.

Now, I hope that you feel more confident in your understanding of chemical reactions!

Chemical Reactions - Key takeaways

  • A chemical reaction is a process that results in the interconversion of chemical species.
  • Synthesis reactions are reactions in which two or more substances combine to form a new substance, whereas decomposition reactions are chemical reactions in which one substance gets converted into 2 or more substances.
  • Redox reactions are reactions in which electrons are transferred from one species (oxidized) to another species (reduced).
  • Combustion reactions are reactions involving a hydrocarbon reacting with oxygen (O2) to produce carbon dioxide (CO2) and water (H2O).
  • Single replacement reactions occur when one element in a compound is replaced by another element.
  • Double replacement reactions occur when two compounds reacts in aqueous solutions, causing the cations and anions of the two reactants to "trade partners or switch places" to form two new compounds.

References

  1. AP ® Chemistry COURSE AND EXAM DESCRIPTION Effective Fall 2020. (n.d.). https://apcentral.collegeboard.org/pdf/ap-chemistry-course-and-exam-description.pdf
  2. David, M., Howe, E., & Scott, S. (2015). Head-Start to A-level Chemistry. Cordination Group Publications (Cgp) Ltd.
  3. Jespersen, N. D., & Kerrigan, P. (2021). AP chemistry premium 2022-2023. Kaplan, Inc., D/B/A Barron’s Educational Series.
  4. Moore, J. T., & Langley, R. (2021). McGraw Hill : AP chemistry, 2022. Mcgraw-Hill Education.
  5. Princeton Review (Firm. (2020). Fast track chemistry : essential review for AP, honors, and other advanced study. The Princeton Review.
  6. Zumdahl, S. S., Zumdahl, S. A., & Decoste, D. J. (2019). Chemistry. Cengage Learning Asia Pte Ltd.

Frequently Asked Questions about Chemical Reactions

During a chemical reaction, different substances combine to form a new substance. When this happens, we see changes in color, gas formation, temperature changes, or even the formation of a precipitate.

Increasing temperature, concentration, and surface area will increase the rate of a chemical reaction. 

A chemical reaction is when different chemicals are combined to produce a new substance.

Enzymes are catalysts that work by increasing the rate of a reaction. They achieve this by lowering the activation energy needed to start a reaction.

In a chemical reaction, reactants are the chemicals on the left side of the equation. Reactants will react with each other to form the product.

Final Chemical Reactions Quiz

Chemical Reactions Quiz - Teste dein Wissen

Question

True or false: chemical reactions consist of reactants and products.

Show answer

Answer

True

Show question

Question

____ are the chemicals on the left side of the chemical equation.

Show answer

Answer

Reactants

Show question

Question

____ are the chemicals on the right side of the equation.

Show answer

Answer

Products

Show question

Question

True or false: The law of conservation of mass states that the mass of products is inversely proportional to the mass of the reactants.

Show answer

Answer

False

Show question

Question

A ________ is an equation where the number of moles of each element on the reactant side is the same as the number of moles on the product side.

Show answer

Answer

Balanced chemical equation

Show question

Question

The steps for balancing chemical equations include the all of the following except:

Show answer

Answer

Write down the unbalanced chemical equation.

Show question

Question

When balancing a chemical equation, how can we find the number of moles of each element?

Show answer

Answer

You multiply the coefficient by the number of elements given by the subscript.

Show question

Question

True or false:  When the number of moles of each element on both sides is equal, then the reaction is balanced.

Show answer

Answer

True

Show question

Question

Types of Chemical Reactions

Show answer

Answer

  • Synthesis reactions (also called combination reactions)
  • Decomposition reactions
  • Single and double replacement reactions
  • Combustion reactions 

  • Redox reactions
  • Acid-base reactions (also called neutralization reactions)
  • Precipitation reactions

Show question

Question

Chemical reactions where two or more reactants produce a single product are called ______ reactions.

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Answer

Synthesis

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______ reactions are chemical reactions where one reactant is broken down to form many products.

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Decomposition

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______ are chemical reactions where the element by itself replaces one of the elements in the compound

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Answer

Single replacement reactions

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Question

_______ reactions are chemical reactions that occur in an aqueous solution. In this type of reaction, the cation (positive ions) and anion (negative ions) of one compound switch places with the cation and anion of the other compound to yield two different products.

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Answer

Double replacement

Show question

Question

Which type of reaction has the general formula:  A + O2 → CO2 + H2O

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Answer

Combustion reaction

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True or false: combustion reactions are considered a type of redox reaction.

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Answer

True

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Question

In ______ reactions, there is a transfer of electrons that happens between the reactants involved in the reaction.

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Answer

 Redox

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OIL RIG means:

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Answer

 Oxidation Is Loss, Reduction Is Gain

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An element that loses electrons will be _____ , while an element that gains electrons will be _____.

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Answer

Oxidized; Reduced

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Elements that are oxidized will have their oxidation numbers _____. 

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Answer

increased

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Elements that are reduced will have their oxidation numbers _____.

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decreased

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What are oxidation numbers?

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Answer

The specific charges on an element that tells whether an element is able to gain, lose or share electrons.

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The ______ is the element is reduced. The ______ is the element that is oxidized.

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Answer

Oxidizing agent; Reducing agent

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True or false: When an acid and a base react together, they form salt and water as products: acid + base → water + salt.

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Answer

True

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Question

Precipitation reactions form a _____ as the product.

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Answer

Precipitate (solid)

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A _____ is defined as an insoluble substance that separates itself from the solution.

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Answer

Precipitate

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Question

Give two examples of inert electrodes used for aqueous solutions. 

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Answer

Graphite or Platinum

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Does electrolysis of aqueous solutions always require water?

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Answer

Yes, to dissolve the compound you are trying to perform electrolysis on. 

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How do you call the positive electrode in electrolysis of aqueous solutions?

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Answer

Anode

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Which one is the cathode?

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negative electrode

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Which reaction occurs at the cathode?

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Reduction

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Oxidation occurs at which electrode?

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Positive

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Gases can be produced only at the anode. 

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Answer

False

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Which gas can be produced at the cathode?

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Answer

Hydrogen gas. 

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Can metal deposit form at the anode? 

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Metal deposit can only form at the cathode. 

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Which gas forms at the anode if the concentration of the anion in the solution is very low?

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Answer

Oxygen gas. 

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If a squeaky pop sound will be heard once a lighted splint is put to one of the produced gases, which gas will it be?

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Hydrogen

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How to tell if oxygen gas has been produced?

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Answer

A glowing split will catch fire again from the presence of oxygen and relight. 

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What test can you perform to know the presence of chlorine gas. 

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Answer

A damp litmus paper will be bleached. 

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How can you quantify if metal deposit has formed on the cathode?

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Answer

Weight the cathode and measure if there is any change in weight. 

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What gas will be produced at the positive electrode in the electrolysis of dilute NaCl?

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Oxygen

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What will be produced at the cathode of the electrolysis of CuOH?

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Answer

Copper metal

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Question

What is activation energy?

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The minimum energy required for a reaction to start

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What does endothermic mean?

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A reaction where energy is transferred from the reaction to the surrounding

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What does exothermic mean?

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The minimum energy required for a reaction to start

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Question

In an exothermic reaction profile, does the products have a higher or lower amount of energy compared to the reactants?


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Answer

Lower

Show question

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In an endothermic reaction profile, does the products have a higher or lower amount of energy compared to the reactants?

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Answer

Lower

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Question

Where can we see activation energy on a reaction profile?


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Answer

The peak of the energy curve

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Question


Is bond breaking exothermic or endothermic?

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Answer

Endothermic

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Question

Is bond forming exothermic or endothermic?

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Answer

Exothermic

Show question

Question

Does bond breaking absorb or release energy?


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Answer

Absorb

Show question

Test your knowledge with multiple choice flashcards

True or false: chemical reactions consist of reactants and products.

____ are the chemicals on the left side of the chemical equation.

____ are the chemicals on the right side of the equation.

Next

Flashcards in Chemical Reactions450

Start learning

True or false: chemical reactions consist of reactants and products.

True

____ are the chemicals on the left side of the chemical equation.

Reactants

____ are the chemicals on the right side of the equation.

Products

True or false: The law of conservation of mass states that the mass of products is inversely proportional to the mass of the reactants.

False

A ________ is an equation where the number of moles of each element on the reactant side is the same as the number of moles on the product side.

Balanced chemical equation

The steps for balancing chemical equations include the all of the following except:

Write down the unbalanced chemical equation.

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