1. sugar + flour + eggs + vanilla + salt  cake
Section 2 Balancing Chemical Equations
Chapter 8
Bellringer
Write a word equation for baking a cake.
Does the cake have the same properties as the ingredients?
Answer:
sugar + flour + eggs + vanilla + salt  cake
The properties are different.

2. What evidence is there that a chemical reaction has occurred?
Chapter 8
Standardized Test Preparation
Read the passage below. Then answer the questions.
A student places a strip of pure magnesium metal into a test tube containing a dilute solution of hydrochloric acid (hydrogen chloride dissolved in water). As the magnesium disappears, bubbles of a colorless gas form and the test tube becomes hot to the touch. If a lit match is placed near the top of the test tube, the gas that has been generated burns.
What evidence is there that a chemical reaction has occurred?

3. Chapter 8
Standardized Test Preparation
Reading Skills
Answer: The gas that burns is a different chemical substance than any of the reactants, indicating a chemical reaction.

4. Chapter 8 Table of Contents Section 1 Describing Chemical Reactions
Chemical Equations and Reactions
Chapter 8
Table of Contents
Section 1 Describing Chemical Reactions
Section 2 Balancing Chemical Equations
Section 3 Classifying Chemical Reactions
Section 4 Writing Net Ionic Equations

5. Reactions Conserve Mass
Section 2 Balancing Chemical Equations
Chapter 8
Reactions Conserve Mass
Mass cannot be created or destroyed by a chemical or physical change
Equations must be balanced.
?Na + ?H2O  ?NaOH + ?H2

6. Chapter 8 Balancing Equations
Section 2 Balancing Chemical Equations
Chapter 8
Balancing Equations
The number of atoms for each element must be the same on the reactants’ side and on the products’ side.
A coefficient multiplies the number of atoms of each element in the formula that follows.
H2O: 2 hydrogen atoms, 1 oxygen atom
2H2O: 4 hydrogen atoms, 2 oxygen atoms

7. Rules for balancing equations
Chapter 8
Section 2 Balancing Chemical Equations
Rules for balancing equations
Identify the names of the reactants and the products, and write a word equation.
Write a formula equation by substituting correct formulas for the names of the reactants and the products.
Balance the formula equation according to the law of conservation of mass.
• Balance the different types of atoms one at a time.
• First balance the atoms of elements that are combined and that appear only once on each side of the equation.
• Balance polyatomic ions that appear on both sides of the equation as single units.
• Balance H atoms and O atoms after atoms of all other elements have been balanced.
4. Count atoms to be sure that the equation is balanced.

8. Section 2 Balancing Chemical Equations

9. Chapter 8 Balancing Equations Sample Problem A
Section 2 Balancing Chemical Equations
Chapter 8
Balancing Equations
Sample Problem A
Balance the equation for the reaction of iron(III) oxide with hydrogen to form iron and water.

10. Chapter 8 Balancing Equations Sample Problem A Solution
Section 2 Balancing Chemical Equations
Chapter 8
Balancing Equations
Sample Problem A Solution
Identify reactants and products.
reactants products
Fe2O H2  Fe + H2O
Count atoms 3 2 3
Reactants
Products
Balanced?
Unbalanced formula equation
Fe2O3 + H2
Fe + H2O
Iron atoms 2 1 no
Oxygen atoms 3
Hydrogen atoms
yes
Insert coefficients.

11. Reactions Conserve Mass
Section 2 Balancing Chemical Equations
Chapter 8
Reactions Conserve Mass
Balanced equations show mass conservation
?Na + ?H2O  ?NaOH + ?H2
2Na + 2H2O  2NaOH + H2
Never change subscripts to balance equations
Unbalanced: H2 + O2  H2O
Incorrect: H2 + O2  H2O2
H2O  H2O2
Correct: 2H2 + O2  2H2O

12. Reactions Conserve Mass
Section 2 Balancing Chemical Equations
Chapter 8
Reactions Conserve Mass

13. Understanding Concepts
Chapter 8
Standardized Test Preparation
Understanding Concepts
6. Write a balanced equation for this reaction:
iron(III) nitrate + lithium hydroxide 
lithium nitrate + iron(III) hydroxide

14. Exit Slip - Understanding Concepts
Chapter 8
Standardized Test Preparation
Exit Slip - Understanding Concepts
6. Write a balanced equation for this reaction:
iron(III) nitrate + lithium hydroxide 
lithium nitrate + iron(III) hydroxide
Fe(NO3)3 + LiOH  LiNO3 + Fe(OH)3
Answer: Fe(NO3)3 + 3LiOH  3LiNO3 + Fe(OH)3