1. Chemical Reactions
Chapter 7 Pg

2. Describing Reactions
Chapter 7 Section 1 Pg

3. Chemical Equations
Reactants- the substances that undergo change in a chemical reaction
Products- the new substances formed as a result of that change
Chemical equation- a representation of a chemical reaction in which the reactants and products are expressed as formulas.

4. Chemical Equations
Example:

5. Conservation of Mass
The law of conservation of mass states that mass in neither created nor destroyed in a chemical reaction.
During chemical reactions, the mass of the products is always equal to the mass of the reactants.
Number of atoms on the left side of the equation equals the number of atoms on the right.

6. Balancing Equations
In order to show that mass is conserved during a reaction, a chemical equation must be balanced.
Balance a chemical equation by changing the coefficients (the number that appears before the formulas)
Never change the subscripts in a formula when balancing equations.

7. Balancing Equations
Step 1: count the number of atoms of each element on each side of the equation
Step 2: change one or more coefficients until the equation is balanced
CH4 + O2 CO2 + H2O unbalanced
C = 1 C = 1
H = 4 H = 2
O = 2 O = 3
balanced

8. Balancing Equations
H O2  H2O
H N2  NH3
Al2O3  Al O2

9. Counting with Moles
Because chemical reactions often involve large numbers of small particles, chemists use a counting unit called the mole to measure amounts of a substance.
A mole (mol) is an amount of a substance that contains approximately 6.02 x 1023 particles (atoms, molecules, or ions) of that substance. This number is known as Avogadro’s number.

10. Counting with Moles Molar Mass The mass of one mole of a substance
The molar mass is the same as its atomic mass expressed in grams. (Ex: C is 12amu, so molar mass of C is 12 g)
A CO2 molecules is composed of one C atom (12 amu) and 2 O atoms (2 x 16amu = 32amu). So CO2 has a molar mass of 44 grams. (add the two amu totals together)

11. Counting with Moles Mole-Mass Conversions
Once you know the molar mass, you can convert moles of that substance into mass or vice versa.
Example: the molar mass of CO2 is 44 grams, which means that one mole of CO2 has a mass of grams. This relationship yields the following conversion factors.
44 g CO mol CO2
1mol CO2 44g CO2

12. Counting with Moles Mole-Mass Conversion (continued)
Suppose you have 55 grams of CO2. To calculate how many moles of CO2 you have, multiply the mass by the conversion factor.
55g CO2 X 1mol CO2 = mol CO2
44g CO2
You can check your answer by using the other conversion factor
1.25mol CO2 X 44g CO2 = 55g CO2
1mol CO2