1. 12.1/12.2 Equations and Chemical Calculations
Chapter 12 Chemical Quantities
12.1/12.2 Equations and Chemical Calculations

2. Chemistry
Today we are learning to:- 1. Examine mole relations in balanced chemical equations
2. Use the molar relationship to gas volumes in chemical equation calculations
3. Use molar relationships in chemical equation calculations

3. Exothermic and Endothermic Processes
17.1
Exothermic and Endothermic Processes
Moles in Balanced Equations
In a fully balanced chemical equation, the coefficients in front of each formula represent the relative amounts of each chemical, reactants and products.
If the coefficient isn’t visible it’s assumed to be 1.
2C2H6(g) + 7O2(g)  4CO2(g) + 6H2O(g)
This ratio of numbers will always be the same for any amount of the substances involved in the reaction
2 moles
7 moles
4 moles
6 moles
So if I had 0.04 mol of ethane (C2H6)
My ratios would be
0.04 moles
0.14 moles
0.08 moles
0.12 moles
To get from the coefficient given in the formula to the number of moles of each substance you just need to set up the ratios and solve for the unknown

4. Exothermic and Endothermic Processes
17.1
Exothermic and Endothermic Processes
Volumes of Gases in Balanced equations
Remember Avogadro’s hypothesis from behavior of gases section:
1 mole of any gas occupies 22.4 L at STP
As the coefficients in a chemical equation are equivalent to the number of moles of reactant and product, it can easily be used to calculate volumes of gases produced in reactions

5. Exothermic and Endothermic Processes
17.1
Exothermic and Endothermic Processes
Volumes of Gases in Balanced equations
Carbon dioxide
Ex.1 How many liters of CO2 will be produced from the complete combustion of 30.0L of ethane (C2H4)
2C2H6(g) + 7O2(g)  4CO2(g) + 6H2O(g)
1. Identify the knowns and unknowns
Volume of C2H6 = 30.0L
Ratio of C2H6:CO2 = 2:4
Volume of CO2 = ?
2. Set up proportion and solve. =
30.0L 2 4 x
x = 60L

6. Exothermic and Endothermic Processes
17.1
Exothermic and Endothermic Processes
Moles of Reactants and Products in Chemical Equations
Remember:
1 mole of any substance = gram formula mass of compound
As the coefficients in a chemical equation are equivalent to the number of moles of reactant and product, it can easily be used to calculate masses of products or reactants

7. Exothermic and Endothermic Processes
17.1
Exothermic and Endothermic Processes
Moles of Reactants and Products in Chemical Equations
Ex.2 How many moles of water will be produced from the complete combustion of 3.0 mol of ethane (C2H4)
2C2H6(g) + 7O2(g)  4CO2(g) + 6H2O(g)
1. Identify the knowns and unknowns
Moles of C2H6 = 3.0 mol
Moles of H2O6 = ?
2. Determine mole ratio from balanced equation
C2H6:H2O = 2:6
3. Set up proportion and solve. =
3.0 mol C2H6
2 mol C2H6
6 mol H2O x
x = 9.0 mol H2O

8. END OF SHOW