1. Chapter 11 Matter and Change 11.1 Describing Chemical Reactions
11.2 Types of Chemical Reactions
11.3 Reactions in Aqueous Solution

2. Introduction to Chemical Equations
Do Now:
Work with your table mates to come up with a list of 10 chemical reactions that you have seen or heard of.

3. How do you know if a chemical reaction is taking place?
Introduction to Chemical Equations
How do you know if a chemical reaction is taking place?

4. Signs of a Chemical Reaction Transfer of energy Change in color
Introduction to Chemical Equations
Signs of a Chemical Reaction
Transfer of energy
Change in color
Production of a gas
Formation of a precipitate

5. How do you describe what is happening in a chemical reaction?
Introduction to Chemical Equations
How do you describe what is happening in a chemical reaction?

6. Word Equations Reactants → Products
Introduction to Chemical Equations
Word Equations
Reactants → Products
Reactants are on the left, products on the right.
An arrow separates them.
You read the arrow as yields, gives, or reacts to produce.

7. Iron + oxygen → iron(III) oxide
Introduction to Chemical Equations
Word Equations
Iron + oxygen → iron(III) oxide
Rusting of Iron
You could say, “Iron reacts with oxygen to produce iron(III) oxide (rust).”

8. Equations that show just the formulas of the reactants and products.
Introduction to Chemical Equations
Skeleton Equations
Equations that show just the formulas of the reactants and products.
Fe + O2 → Fe2O3
The first step in writing a complete chemical equation is to write the skeleton equation.

9. Symbols Used in Chemical Equations
Interpret Data
Symbols Used in Chemical Equations
Symbol
Explanation +
Separates two reactants or two products →
“Yields,” separates reactants from products
Use in place of → for reversible reactions
(s), (l), (g)
Designates a reactant or product in the solid state, liquid state, or gaseous state; placed after the formula
(aq)
Designates an aqueous solution; the substance is dissolved in water; placed after the formula
Indicates that heat is supplied to the reaction
A formula written above or below the yields sign indicates its use as a catalyst (in this example, platinum). Δ
heat Pt

10. Introduction to Chemical Equations
Indicate the physical states of substances by putting a symbol after each formula.
(s) for solid
(l) for liquid,
(g) for gas,
(aq) for a substance in an aqueous solution (a substance dissolved in water).
Fe(s) + O2(g) → Fe2O3(s)

11. Chemical Equations H2O2(aq) H2O(l) + O2(g)
Introduction to Chemical Equations
Chemical Equations
Catalyst: substance that speeds up the reaction but is not used up in the reaction.
A catalyst is neither a reactant nor a product, so its formula is written above the arrow in a chemical equation.
H2O2(aq) H2O(l) + O2(g)
MnO2

12. Write a Skeleton Equation
Sample Problem 11.1
Write a Skeleton Equation
Hydrochloric acid reacts with solid sodium hydrogen carbonate. The products formed are aqueous sodium chloride, water, and carbon dioxide gas. Write a skeleton equation for this chemical reaction.

13. Write a Skeleton Equation
Sample Problem 11.1
Write a Skeleton Equation
Hydrochloric acid reacts with solid sodium hydrogen carbonate. The products formed are aqueous sodium chloride, water, and carbon dioxide gas. Write a skeleton equation for this chemical reaction.
NaHCO3(s) + HCl(aq) → NaCl(aq) + H2O(l) + CO2(g)

14. Law of Conservation of Mass
Balancing Chemical Equations
Law of Conservation of Mass
During any chemical reaction, the mass of the products always equals the mass of the reactants.
Atoms are neither created nor destroyed in ordinary chemical reactions.
The same number of atoms of each element must be present on both sides of the equation.

15. What does that mean for you?
Balancing Chemical Equations
What does that mean for you?
The same number of atoms of each element must be present on both sides of the equation.
Add coefficients to balance the reactants and products. Do not add subscripts!

16. Balancing Chemical Equations
Coefficients— small whole numbers that are placed in front of the formulas in an equation in order to balance it.

17. Balancing Chemical Equations
Balanced equation: each side of the equation has the same number of atoms of each element and mass is conserved.

18. To write a balanced chemical equation 1. Write the skeleton equation.
Balancing Chemical Equations
To write a balanced chemical equation
1. Write the skeleton equation.
2. Use coefficients to balance the equation so that it obeys the law of conservation of mass.

19. Carbon burns in the presence of oxygen to produce carbon dioxide.
Balancing Chemical Equations
Carbon burns in the presence of oxygen to produce carbon dioxide.
C(s) Carbon +
O2(g) Oxygen
CO2(g) Carbon dioxide
Reactants 1 carbon atom, 2 oxygen atoms
Product 1 carbon atom, 2 oxygen atoms
This equation is balanced.
You do not need to change the coefficients.
They are all understood to be 1.

20. When hydrogen and oxygen are mixed, the product is water.
Balancing Chemical Equations
When hydrogen and oxygen are mixed, the product is water.
The formulas for all the reactants and the product are correct, but this equation is not balanced.
As written, the equation does not obey the law of conservation of mass.

21. When hydrogen and oxygen are mixed, the product is water.
Balancing Chemical Equations
When hydrogen and oxygen are mixed, the product is water.
If you put the coefficient 2 in front of H2O, oxygen will be balanced.
Now twice as many hydrogen atoms are in the product as are in the reactants.

22. When hydrogen and oxygen are mixed, the product is water.
Balancing Chemical Equations
When hydrogen and oxygen are mixed, the product is water.
To correct this equation, put the coefficient 2 in front of H2.
The equation is now balanced.

23. CHEMISTRY & YOU
The reaction between oxygen and hydrogen in fuel cells produces the energy to power a car. What are the products of the reaction in a fuel cell that make the fuel-cell car a zero-emission car?

24. CHEMISTRY & YOU
The reaction between oxygen and hydrogen in fuel cells produces the energy to power a car. What are the products of the reaction in a fuel cell that make the fuel-cell car a zero-emission car?
Water is the product of the reaction between oxygen and hydrogen in a fuel cell. Water is not a pollutant, and so fuel-cell cars are considered “zero-emission” cars.

25. Rules for Writing and Balancing Equations
Interpret Data
Rules for Writing and Balancing Equations
1. Determine the correct formulas for all the reactants and products.
2. Write the skeleton equation by placing the formulas for the reactants on the left and the formulas for the products on the right with a yields sign (→) in between. If two or more reactants or products are involved, separate their formulas with plus signs.
3. Determine the number of atoms of each element in the reactants and products. Count a polyatomic ion as a single unit if it appears unchanged on both sides of the equation.
4. Balance the elements one at a time by using coefficients. When no coefficient is written, it is assumed to be 1. Begin by balancing elements that appear only once on each side of the equation. Never balance an equation by changing the subscripts in a chemical formula. Each substance only has one correct formula.
5. Check each atom or polyatomic ion to be sure that the number is equal on both sides of the equation.
6. Make sure all the coefficients are in the lowest possible ratio.

26. AgNO3(aq) + Cu(s) → Cu(NO3)2(aq) + Ag(s)
Sample Problem 11.2
Balancing a Chemical Equation
Students suspended copper wire in an aqueous solution of silver nitrate. They noticed a deposit of silver crystals on the copper wire when the copper reacted with the silver nitrate. They recorded the equation for this reaction but didn’t balance it. Balance their equation:
AgNO3(aq) + Cu(s) → Cu(NO3)2(aq) + Ag(s)

27. 2AgNO3(aq) + Cu(s) → Cu(NO3)2(aq) + Ag(s)
Sample Problem 11.2
Solve Apply concepts to this situation. 2
Balance the nitrate ion.
Put a coefficient 2 in front of AgNO3(aq).
2AgNO3(aq) + Cu(s) → Cu(NO3)2(aq) + Ag(s)
Remember that a coefficient must always go in front of a compound’s formula, not in the middle of it.

28. 2AgNO3(aq) + Cu(s) → Cu(NO3)2(aq) + 2Ag(s)
Sample Problem 11.2
Solve Apply concepts to this situation. 2
Balance the silver.
Put a coefficient 2 in front of Ag(s).
2AgNO3(aq) + Cu(s) → Cu(NO3)2(aq) + 2Ag(s)

29. Balancing a Chemical Equation
Sample Problem 11.3
Balancing a Chemical Equation
Aluminum is a good choice for outdoor furniture because it reacts with oxygen in the air to form a thin protective coat of aluminum oxide. Balance the equation for this reaction.
Al(s) + O2(s) → Al2O3(s)

30. Analyze Identify the relevant concepts.
Sample Problem 11.3
Analyze Identify the relevant concepts. 1
Apply the rules for balancing equations.
Notice the odd number of oxygen atoms in the product.
Al(s) + O2(s) → Al2O3(s)

31. Solve Apply concepts to this situation.
Sample Problem 11.3
Solve Apply concepts to this situation. 2
First balance the aluminum by placing the coefficient 2 in front of Al(s).
2Al(s) + O2(s) → Al2O3(s)

32. Solve Apply concepts to this situation.
Sample Problem 11.3
Solve Apply concepts to this situation. 2
Multiply the formula with the odd number of oxygen atoms (on the right) by 2 to get an even number of oxygen atoms on the right.
2Al(s) + O2(s) → 2Al2O3(s)
Any whole-number coefficient placed in front of O2 will always give an even number of oxygen atoms on the left.

33. Solve Apply concepts to this situation.
Sample Problem 11.3
Solve Apply concepts to this situation. 2
Balance the oxygens on the left by placing a 3 in front of O2.
2Al(s) + 3O2(s) → 2Al2O3(s)

34. Solve Apply concepts to this situation.
Sample Problem 11.3
Solve Apply concepts to this situation. 2
Then rebalance the aluminum by changing the coefficient of Al(s) from 2 to 4.
4Al(s) + 3O2(s) → 2Al2O3(s)

36. C3H8(g) + O2(g) → CO2(g) + H2O(l)
Balance the following equation.
C3H8(g) + O2(g) → CO2(g) + H2O(l)

37. C3H8(g) + O2(g) → CO2(g) + H2O(l)
Balance the following equation.
C3H8(g) + O2(g) → CO2(g) + H2O(l)
C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(l)

38. END OF 11.1