4B1 Balancing Equations

Question 1

What does the law of conservation of matter state?

Answer 1

Matter cannot be created or destroyed; it can only be rearranged.

This means every molecule in a reaction must be accounted for.

Question 2

Define:

balanced chemical equation

Answer 2

An equation showing the ratio of reactants and products with an equal number of atoms for each element on both sides of the equation.

Balancing ensures the law of conservation of matter is followed.

Question 3

What is a word equation?

Answer 3

An equation that uses names of chemicals instead of formulas.

Example: glucose + oxygen → carbon dioxide + water.

Converting a word equation to a formula equation is the first step in balancing.

Question 4

How do you convert a word chemical equation into a formula?

Answer 4

By writing the chemical symbols for each reactant and product involved in the reaction.

Example: Sodium is Na, Water is H₂O.

Question 5

Fill in the blank:

The number written before a chemical in an equation is called a ______.

Answer 5

coefficient

Coefficients indicate how many molecules or moles of a substance participate in the reaction.

Question 6

True or False:

Subscripts in chemical formulas can be changed when balancing chemical equations.

Answer 6

False

Only coefficients can be adjusted when balancing equations; changing subscripts alters the identity of the molecules involved.

Subscripts define the compound’s composition and cannot be modified without changing the reaction.

Question 7

How are the coefficients used in balancing chemical equations?

Answer 7

They are used to adjust the number of molecules to ensure that each element has the same number of atoms on both sides of the equation.

They multiply the number of atoms in a molecule without changing the molecule’s identity.

Question 8

List five steps to balance a chemical equation.

Answer 8

1. Change a word equation into a formula.
2. Balance single-molecule atoms one at a time.
3. Balance non-H/O atoms.
4. Balance H and O.
5. Count atoms to verify balance.

This sequence minimizes trial and error and ensures accuracy in balancing.

Question 9

How do you check if a chemical equation is balanced?

Answer 9

Count the number of atoms for each element on both sides and ensure they are equal.

Question 10

Which atoms are typically balanced last in chemical equations?

Answer 10

Hydrogen and oxygen atoms.

These atoms are often present in multiple compounds, making them easier to balance after other atoms.

Question 11

What is the purpose of balancing non-H/O atoms before H and O?

Answer 11

It simplifies the balancing process by addressing elements that are less likely to be in multiple compounds first.

This reduces the complexity of balancing elements like hydrogen and oxygen.

Question 12

Fill in the blank:

In the reaction of sodium and water, the balanced equation is 2Na + 2H₂O → _______.

Answer 12

2NaOH + H₂

This reaction balances sodium, hydrogen, and oxygen atoms to comply with the conservation law.

Question 13

Fill in the blank:

In the potassium and carbon dioxide reaction, the balanced equation is 2K + CO₂ → _______.

Answer 13

K₂CO₃

This balances potassium, carbon, and oxygen atoms in the reaction.

Question 14

True or False:

A balanced chemical equation always uses whole number coefficients.

Answer 14

True

Whole numbers ensure the reaction represents physical reality since partial molecules do not exist.

Question 15

What is the relationship between coefficients and moles in a balanced equation?

Answer 15

Coefficients indicate the mole ratio of reactants and products in the reaction.

This ratio helps predict quantities involved in a chemical reaction.

Question 16

Define:

oxidizing agent

Answer 16

A compound that accepts electrons, decreasing its oxidation state.

Oxidizing agents are also known as oxidants or oxidizers.

Question 17

Define:

reducing agent

Answer 17

A compound that donates electrons, increasing its oxidation state.

Reducing agents are also known as reductants.

Question 18

What happens to the oxidizing agent in a reaction?

Answer 18

It gets reduced.

The oxidizing agent accepts electrons, becoming reduced in the process.

Question 19

What happens to the reducing agent in a reaction?

Answer 19

It gets oxidized.

The reducing agent donates electrons, becoming oxidized in the process.

Question 20

List four examples of oxidizing agents.

Answer 20

1. Oxygen
2. Ozone
3. Halogens
4. Sulfuric acid

These compounds can accept electrons and oxidize other substances.

Question 21

List four examples of reducing agents.

Answer 21

1. Sodium
2. Magnesium
3. Aluminum
4. Hydrogen

These compounds readily donate electrons to reduce other substances. These tend to be atoms with low electronegativity, low oxidation states, or a large atomic radius.

Question 22

True or False:

An oxidizing agent releases electrons.

Answer 22

False

An oxidizing agent accepts electrons.

Question 23

True or False:

A reducing agent gains electrons.

Answer 23

False

A reducing agent loses electrons.

Question 24

How can an oxidizing agent release oxygen?

Answer 24

By transferring oxygen to another compound.

This process is one way oxidizing agents facilitate oxidation.

Question 25

How does a reducing agent **release hydrogen**?

Answer 25

By **transferring hydrogen** to another compound. ## Footnote This is one method by which reducing agents facilitate reduction.

Question 26

What is the term for a reaction where **oxidation and reduction occur simultaneously**?

Answer 26

A redox reaction ## Footnote Redox reactions involve both oxidation and reduction processes occurring together.

Question 27

What are the *four* types of **redox reactions**?

Answer 27

1. Combination 1. Decomposition 1. Combustion 1. Displacement ## Footnote These reaction types involve changes in oxidation states of compounds.

Question 28

Which side of an **oxidation half-reaction** shows electrons?

Answer 28

The **right** (product) side. ## Footnote In oxidation, electrons are lost and appear on the product side of the equation.

Question 29

Which side of a **reduction half-reaction** shows electrons?

Answer 29

The **left** (reactant) side. ## Footnote In reduction, electrons are gained and appear on the reactant side of the equation.

Question 30

How do you **identify the oxidizing agent** in a reaction?

Answer 30

Look for the compound with a **decrease in oxidation state**. ## Footnote The oxidizing agent is reduced in the process.

Question 31

How do you **identify the reducing agent** in a reaction?

Answer 31

Look for the compound with an **increase in oxidation state**. ## Footnote The reducing agent is oxidized in the process.

Question 32

What happens to the oxidation number of a **reducing agent**?

Answer 32

It increases. ## Footnote The reducing agent donates electrons, increasing its oxidation state.

Question 33

What happens to the oxidation number of an **oxidizing agent**?

Answer 33

It decreases. ## Footnote The oxidizing agent gains electrons, decreasing its oxidation state.

Question 34

# True or False: Redox reactions **always involve** both an oxidizing and reducing agent.

Answer 34

True ## Footnote Oxidation and reduction processes are inseparable in redox reactions.

Question 35

What is a **combination** reaction?

Answer 35

A reaction where **two compounds combine** to form one compound. ## Footnote Example: 2H₂ + O2 → 2H₂O

Question 36

What is a **decomposition** reaction?

Answer 36

A reaction where **one compound breaks down** into two compounds. ## Footnote Example: NaCl → Na + Cl

Question 37

What is a **combustion** reaction?

Answer 37

A reaction where an **organic fuel reacts with oxygen** to produce water and carbon dioxide. ## Footnote Example: CH₄ + O₂ → CO₂ + H₂O

Question 38

What is a **displacement** reaction?

Answer 38

A reaction where **elements in two compounds swap places** to form two new elements. ## Footnote Example: Zn + CuCl₂ → ZnCl₂ + Cu

Question 39

What is the **oxidation half-reaction**?

Answer 39

A half reaction that shows **only the process of oxidation**. ## Footnote It does not include the oxidizing agent, which is assumed.

Question 40

What is the **reduction half-reaction**?

Answer 40

A half reaction that shows **only the process of reduction**. ## Footnote It does not include the reducing agent, which is also assumed.

Question 41

How can you tell if a reaction is **not a redox reaction**?

Answer 41

If **only one compound changes oxidation state** without involving other compounds. ## Footnote For example, in HCl + NaOH → H₂O + NaCl, only one compound changes.