Gas Stoichiometry

Molar Volume of Gases The volume occupied by one mole of a gas at STP (standard temperature and pressure) –Equal to 22.4 L / mol –Can be used as a conversion factor – OR

Sample Problem 1

Sample Problem 2

PRACTICE: You Try It! 1.What is the volume of 77.0 g nitrogen dioxide gas at STP? 37.5 L NO 2 2.At STP, 3 L of chlorine is produced during a chemical reaction. What is the mass of this gas? 9 g Cl 2

Gas Stoichiometry Moles  Liters of a Gas: –STP Conditions use 22.4 L/mol and stoichiometry –Non-STP Conditions use ideal gas law and stoichiometry General rule: FIND MOLES FIRST! –If given volume of gas – Non-STP 1.Use ideal gas law to find moles 2.Use stoichiometry to convert moles to final answer –If given volume of gas – STP 1. Use molar volume (22.4 L/mol) to find moles 2. Use stoichiometry to convert moles to final answer

Gas Stoichiometry –If you need the volume of gas – Non-STP 1.Use stoichiometry to convert to moles of needed gas 2.Use the ideal gas law to find volume –If you need the volume of gas – STP 1.Use stoichiometry to convert to moles of needed gas 2.Use the molar volume (22.4L/mol) to find volume

1 mol C 2 H g C 2 H 6 Gas Stoichiometry Problem How many liters of CO 2 form when g of C 2 H 6 combusts at STP? g C 2 H 6 1 = mol CO 2 2C 2 H 6 + 7O 2  6H 2 O + 4CO 2 4 mol CO 2 2 mol C 2 H 6 Need: liters 1.Use stoich to calculate moles of CO 2 2.Use the molar volume to find liters Use the molar volume to find liters.

22.4 L CO 2 1 mol CO 2 Gas Stoichiometry Problem How many liters of CO 2 form when g of C 2 H 6 combusts at STP? mol CO 2 1 = L CO 2 2C 2 H 6 + 7O 2  6H 2 O + 4CO 2 Courtesy Christy Johannesson

1 mol CaCO g CaCO 3 Gas Stoichiometry Problem What volume of CO 2 forms from 5.25 g of CaCO 3 decomposing at 103 kPa & 25ºC? 5.25 g CaCO 3 1 = mol CO 2 CaCO 3  CaO + CO 2 1 mol CO 2 1 mol CaCO 3 Need: liters 1.Use stoich and calculate moles of CO 2., 2.Use the ideal gas law. Plug this into the Ideal Gas Law to find liters.

WORK: Convert units first! Then apply PV = nRT Ans: 1.26 L CO 2 Gas Stoichiometry Problem What volume of CO 2 forms from 5.25 g of CaCO 3 at 103 kPa & 25ºC? GIVEN: P = 103 kPa V = ? n = 1.26 mol T = 25°C R = L  atm/mol  K

WORK: Convert units first! Then apply PV = nRT Gas Stoichiometry Problem How many grams of Al 2 O 3 are synthesized from 15.0 L of O 2 at 97.3 kPa & 21°C? GIVEN: P = 97.3 kPa V = 15.0 L n = ? T = 21°C R = L  atm/mol  K Al + O 2  Al 2 O 3 Given: liters 1.Use Ideal Gas Law and calculate moles of O 2., 2.Use stoich to find grams of Al 2 O 3 NEXT  use stoich to find grams

2 mol Al 2 O 3 3 mol O 2 Gas Stoichiometry Problem How many grams of Al 2 O 3 are formed from 15.0 L of O 2 at 97.3 kPa & 21°C? mol O 2 1 = 40.6 g Al 2 O 3 4 Al + 3 O 2  2 Al 2 O g Al 2 O 3 1 mol Al 2 O 3 Use stoich to convert moles of O 2 to grams Al 2 O 3.

You Try It!! Find the volume of hydrogen gas made when 38.2 g zinc reacts with hydrochloric acid at a pressure of kPa and a temperature of 88 o C. HINT: –Use stoich to find moles of H 2 first, then use the ideal gas law. Zn (s) + 2 HCl (aq)  ZnCl 2 (aq) + H 2 (g) ANSWER: 16.3 L H 2

You Try It!! What mass of solid magnesium is required to react with 250 mL carbon dioxide at 1.5 atm and 77 o C to produce solid magnesium oxide and solid carbon? HINT: –Use ideal gas law to find moles of CO2, then use stoich to find grams of Mg. ANSWER: 0.63 g Mg