Chapter 5 - Balancing Equations

Steps for balancing-

  1. Find the reaction ( what are the products, reactants, and states)

  2. Write the unbalanced equation

  3. make a table of numbers of elements on both sides of the reaction

  4. balance each equation

  • NEVER CHANGE THE FORMULA OF A REACTANT OR PRODUCT

  • NEVER ADD NEW REACTANTS OR PRODUCTS TO THE EQUATION

  • USE THE SMALLEST POSSIBLE WHOLE NUMBER COEFFICIENTS

Stoichiometry- the study of the quantitative relationships between reactants and products in a chemical reaction.It uses balanced chemical equations to calculate the exact amounts of substances consumed and produced.the study of the quantitative relationships between reactants and products in a chemical reaction. It uses balanced chemical equations to calculate the exact amounts of substances consumed and produced.

For example:

  • If you have the balanced reaction

2H2+O2→2H2O2H2​+O2​→2H2​O

stoichiometry lets you calculate how many moles (or grams) of H2OH2​O are formed when a certain amount of H2H2​reacts with O2O2​.

The recipe for the reaction 

mole - mole 


  1. Write and balance the chemical equation.

  2. Convert given information into moles (using molar mass if needed).

  3. Use mole ratios from the balanced equation to find moles of what you want.

  4. Convert back to grams, liters (if gas), or particles (if asked).

3.

Essential Conversion Factors

  • Moles ↔ Grams
    \text{Moles} = \frac{\text{Mass (g)}}{\text{Molar Mass (g/mol)}}

  • Moles ↔ Particles
    \text{Particles} = \text{Moles} \times (6.022 \times 10^{23})

  • Moles ↔ Volume (gas at STP)
    \text{Volume (L)} = \text{Moles} \times 22.4 \, L

4.

Types of Problems

A.

Mass-Mass

Example:

2H_2 + O_2 \rightarrow 2H_2O

How many grams of water are produced from 4.00 g of H₂?

Steps:

  1. Convert H₂ grams → moles.

  2. Use ratio 2H₂ : 2H₂O.

  3. Convert moles H₂O → grams.

B.

Limiting Reactant

  • Find moles of each reactant.

  • Compare ratios → the smaller amount (based on balanced equation) is the limiting reactant.

C.

Percent Yield

\text{Percent Yield} = \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \times 100

D.

Mole-Particle or Mole-Volume

  • Use Avogadro’s number (6.022 × 10²³) or 22.4 L/mol at STP.

Gram - gram

1. FROM THE BALANCED
REACTION FIND THE MOLES
2. FIND THE MOLAR MASS
OF EACH COMPOUND
4. GET A RATIO OF THE
GRAMS OF MATERIALS
3. MULTIPLY THE MOLAR
MASS BY THE COEFFICIENT
5.SET THAT RATIO TO THE
GIVEN AMOUNT

Dimensional Analysis Method

START WITH g OF MATERIAL
CONVERT TO MOLES
(DIVIDE BY MOLAR MASS)
ALWAYS COMPARE MOLES TO
MOLES, NOT GRAMS TO GRAMS

percent yield formula : actual/theoretical x 100