Information in Chemical Equations (Balancing) Remember, the Law of Conservation of Mass states that atoms (mass) can’t be created or destroyed during a reaction. The same amount of each atom must be present in the reactants and products. Example: If 5g of hydrogen mix with 3g of oxygen, how much water would be produced? Answer = 8g of water Example: If 16g of copper reacts with oxygen to produce 21.5g of copper oxide, how much oxygen was needed? Answer = 5.5g of oxygen

We balance chemical equations so that they follow the law of conservation of mass. The coefficients change the number of any given molecule in the equation. The mass of the reactants will equal the mass of the products in a balanced equation.

STEPS TO BALANCE AN EQUATION: 1. Write the word equation. 2. Write the skeleton equation (unbalanced chemical formula). 3. Count the number of atoms in the reactants and products. 4. Multiply each formula by the correct coefficient to balance the number of atoms on each side of the equation. START with atoms that appear the least number of times and leave oxygen and hydrogen for the end. 5. Check the number of atoms on each side in the comparison table.

Balancing Equations Example 1: Magnesium reacts with oxygen to produce magnesium oxide. Write the word equation Magnesium and Oxygen reacts to form Magnesium Oxide Mg + O2 → MgO Write the skeleton chemical equation Count the number of each atom in the reactants and the products. Reactants Products Mg 1 O 2

Multiply the formulas by the correct coefficient Multiply the formulas by the correct coefficient. Start with the atoms that appear the least number of times and leave oxygen and hydrogen until the end. Reactants Products Mg 1 O 2 Mg + O2 → MgO Reactants Products Mg 1 2 O Mg + O2 → 2 MgO Reactants Products Mg 2 O 2 Mg + O2 → 2 MgO

Example: Methane and Oxygen react to form Carbon Dioxide and Water   _____ CH4 + _____ O2  _____ CO2 + _____ H2O Check to see that the number of atoms in the reactants and products match. Reactants Products C H O

Example: Methane and Oxygen react to form Carbon Dioxide and Water Reactants Products C 1 H 4 2 O 3 CH4 + O2  CO2 + H2O Reactants Products C 1 H 4 O 2 CH4 + O2  CO2 + 2 H2O Reactants Products C 1 H 4 O CH4 + 2 O2  CO2 + 2 H2O

Zinc + Silver nitrate  Zinc nitrate and Silver Example: Zinc and Silver nitrate react to form Zinc nitrate and Silver.   Zinc + Silver nitrate  Zinc nitrate and Silver _____ Zn + _____ Ag (NO3)  _____ Zn (NO3)2 + _____ Ag Check to see that the number of atoms in the reactants and products match. Reactants Products Zn 1 Ag N 2 O 3 6

Example: Zinc and Silver nitrate react to form Zinc nitrate and Silver. Reactants Products Zn 1 Ag N 2 O 3 6 Zn + Ag(NO3)  Zn(NO3)2 + Ag Reactants Products Zn 1 Ag 2 N O 6 Zn + 2 Ag(NO3)  Zn(NO3)2 + Ag

Reactants Products Zn 1 Ag 2 N O 6 Zn + 2 Ag(NO3)  Zn(NO3)2+ 2 Ag

Now practice…….. Write a balanced equation for the reaction between potassium and bromine to make potassium bromide. Write a balanced chemical equation for the reaction between oxygen and pentane (C5H12) to produce carbon dioxide and water. Write a balanced chemical equation for the reaction between iron (III) nitrate and sodium hydroxide to produce iron (III) hydroxide and sodium nitrate.