1. Chapter 6: Chemical Reactions: An Introduction
Section 6.1: Evidence for a Chemical Reaction
Section 6.2: Chemical Equations
Section 6.3: Balancing Chemical Equations

2. 6.1: Evidence for a Chemical Reaction
Objective: To learn the signals that show a chemical reaction has occurred.

3. Steel (smooth, shiny) to rust (reddish-brown, flaky)
Hair changes color when its bleached
Nylon is formed from 2 liquids
Blue flame is seen when natural
Gas combines with oxygen
Unexpected reactions
Ammonia + Bleach give chloramines
toxic gases
Demonstration of a chemical reaction

4. 6.2: Chemical Equations
Objective: To learn to identify the characteristics of a chemical reaction and the information given by a chemical equation.

5. CHEMICAL Reaction: chemical change
Chemical Equation: representation of a
chemical reaction.
Reactants Products
Methane + Oxygen Carbon Dioxide + Water
CH O CO H2O
Chemical reaction involves changing the
ways the atoms are grouped.
Atoms are not created or destroyed.
All atoms are present in the reactants
Must be accounted for in the products.
BALANCING THE CHEMICAL REACTION
Obeys this rule.

6. The chemical equation for a reaction provides
CH O CO H2O
C H H
H H
O O
C O O
H H O
C H H
H H
O O
O O
C O O
H H O
H H O
CH O CO H2O
The chemical equation for a reaction provides
The identities of the reactants and products
The relative numbers of each

7. Physical States Symbol State (s) Solid (l) Liquid Gas
(aq) dissolved in water(in aqueous solution)

8. 6.3: Balancing Chemical Equations
Objective: To learn how to write a balanced equation for a chemical reaction

9. Balancing a Chemical Reaction
Atoms are conserved in a chemical reaction
The identities (formulas) of the compound must never be changed in balancing a chemical equation.
Coefficients: integers used to balance an
Equation.

10. Balancing a Chemical Reaction
Liquid ethanol (C2H5OH) reacts with gaseous oxygen to produce gaseous carbon dioxide and gaseous water.
Step 1:
C2H5OH(l) + O2(g) CO2(g) + H2O(g)
Step 3 and Step 4:
C2H5OH(l) + 3O2(g) CO2(g) + 3H2O(g)

11. Balancing a Chemical Reaction
Solid potassium reacts with liquid water to form gaseous hydrogen and potassium hydroxide that dissolves in the water.
Step 1:
K(s) + H2O(l) H2(g) + KOH(aq)
2K(s) + H2O(l) H2(g) +2KOH(aq)

12. Balancing a Chemical Reaction
Ammonia gas reacts with oxygen gas to produce gaseous nitrogen monoxide (nitric oxide) and gaseous water.
Step 1:
NH3(g) + O2(g) NO(g) + H2O(g)
4NH3(g) +5O2(g) NO(g) +6H2O(g)