1. The Arithmetic of Equations

2. Using Everyday Equations
A balanced chemical equation provides the same kind of quantitative information that a recipe does.
If we know that in order to manufacture a tricycle we need the frame (F), the seat (S), the wheels (W), the handlebars (H), and the pedals (P), these would be the reactants needed to produce a tricycle, the product, then by balancing this equation we can figure out how many reactants we would need to manufacture any number of products.

3. Example
Using F, S, W, H, and P and ending with the product FSW3HP2 (A tricycle): What would the equation be to produce one tricycle would be: F + S + 3W + H + 2P ----> FSW3HP2 This balanced equation is the “recipe” for a single tricycle.

4. Using Balanced Equations
Chemists use balanced equations as a basis to calculate how much reactant is needed, or product is formed in a reaction.
Stoichiometry – The calculations of quantities in chemical reactions.
This allows chemists to tally the amounts of reactants and products using ratios of moles or representative particles.

5. Interpreting Chemical Equations
A balanced equation can be interpreted in terms of different quantities, including number of atoms, molecules or moles; mass; and volume.
The following equation shows the synthesis of ammonia (a common fertilizer)
N2(g) + 3H2 (g) ---->2NH3(g)
What are the total number of atoms, molecules, moles, mass and volume on both the reactant and product side of this equation?
Reactant Side Product side
Atoms
Molecules
Moles
Mass g g
Volume L L

6. Mass Conservation in Chemical Reactions
Mass and Atoms are conserved in every chemical reaction
Let’s try one:
Interpret the equation for the formation of water from its elements in terms of number of molecules and moles, and volume of gasses at STP.
2H2(g) + O2(g) ----> 2H2O (g)
2 molecules of H2 + 1 molecule of O2 ----> 2 molecules of H2O
2 moles of H2 + 1 mole of O2 ----> 2 moles of H2O
44.8 L of H L of O2 ----> 44.8 L of H2O

7. 12.1 pg. 389 #'s 9-10
Read 12.2 pgs