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

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

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

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

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

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

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

END OF SHOW