HC 7.3 Balancing Equations

Chapter 7

Chemical Reactions: An Introduction

Steven S. Zumdahl

Susan A. Zumdahl

Donald J. DeCoste

Gretchen M. Adams • University of Illinois at Urbana-Champaign

• Write a balanced equation for a chemical reaction

Core Ideas and Skills

Balancing Chemical Equations

Section 7.3

• A chemical reaction is balanced using a systematic approach:

▪ Write the formulas of the reactants and products to give the

unbalancedchemical equation.

▪ Balance by trial and error starting with the most complicated molecule.

▪ At the end, check that the coefficients used give the same number of

each type of atom on both sides of the arrow.

Balancing Chemical Equations

Section 7.3

Multiple Select

When balancing this chemical equation, which molecule should you start with?

H₂ + O₂ → H₂O

(Choose 2 answers)

• H₂

• O₂

• H₂O

• the most complex molecule

• the simplest molecule

Multiple Choice

In a balanced chemical equation, what must be the same on both sides of the arrow?

• the number of molecules

  (of each type)

• the number atoms (of each type)

• the number of products must equal the number of reactants

• the same coefficients must be used on both sides

Multiple Choice

What does the coefficient in a chemical equation represent?

• number of molecules

• number of atoms

• speed of reaction

• temperature of reaction

Hydrogen gas and oxygen gas combine to form liquid water.

Example

Balancing Chemical Equations

Section 7.3

Multiple Select

Hydrogen gas and oxygen gas combine to form liquid water.

Which would be correct for the 1st step? Choose all correct answers.

• H₂(g) + O₂(g) → H₂O(l)

• H₂ + O₂ → H₂O

• H + O → H₂O

Drag and Drop

Hydrogen gas and oxygen gas combine to form liquid water.

Add coefficients to balance the equation.

​

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H₂(g) + ​

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O₂(g) → ​

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H₂O(l)

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2

1

3

4

Drag and Drop

Count the number of atoms on each side to make sure its balanced:

​ 2H₂(g) + ​ O₂(g) → 2H₂O(l)

​

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H​

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​

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O​

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3

4

2

1

Multiple Choice

Is the following equation balanced?...
Al + O₂ --> 2Al₂O₃

• Yes!
• No!

Multiple Choice

Is the following equation balanced?
2C₂H₂ + 5O₂ --> 4CO₂ + 2H₂O

• yes
• no

Multiple Choice

Balance the following equation:

___ Mg+ ___ O₂→___ MgO

• 1, 1, 3

• 2, 1, 2

• 1, 2, 1

• 2, 2, 2

Multiple Choice

Balance the following equation:

___ SeCl₆+ ___ O₂→___ SeO_{2+____}Cl₂

• 1, 1, 1, 3

• 2, 1, 2, 1

• 1, 2, 1, 2

• 2, 2, 2, 4

Drag and Drop

Balance the equation below:

​

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CaO + ​

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C → ​

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CaC₂ + ​

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CO₂

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2

5

1

0

3

4

6

7

8

9