1. 14.1 Chemical Reactions
ANNE - 1: start at 7; 2: done; 3: start at 6; 4: done

2. Chemical Reactions
Chemical reaction: the process of breaking chemical bonds and reforming new bonds to make new substances

3. Evidence of Chemical Change
Four indicators of a chemical change:
1. Formation of new gas
2. Formation of new solid
3. Release of energy (heat or light)
4. Color change

4. Reactants and Products
Reactant: starting substance(s)
Product: new substance(s) formed

5. Reaction Symbols
arrow = “to produce”
The small symbols in the parentheses (s, l, g, aq) indicate the phase of each substance in the reaction.
Symbol
Meaning
(s)
solid
(l)
liquid
(g)
gas
(aq)
aqueous - dissolved in solution

6. Law of Conservation of Mass
Mass of reactants = mass of products

7. A Reminder: Numbers in Chemical Formulas

8. Balancing Chemical Equations
The law of conservation of mass tells us that atoms and molecules must be balanced on both sides of a chemical equation.

9. Balancing Chemical Equations
coefficient
subscript
Rules:
Subscripts (small numbers) CANNOT be changed.
Coefficients (big numbers) can be placed in front of the chemical formula.
A coefficient applies to ALL atoms in the chemical formula.
Multiply coefficients by subscripts to get the total atoms.

10. Balancing Chemical Equations Example #1
___Cu2S + ___ O2 → ___ Cu2O + ___ SO2

11. Balancing Chemical Equations Example #2
___ Al + ___ O2 → ___ Al2O3

12. Balancing Chemical Equations EXIT SLIP
___ CO2 + ___ H2 → ___ CH4 + ___ H2O