1. Gas Stoichiometry!

2. equal volumes of gases at the same temperature & pressure contain equal numbers of particles equal volumes of gases at the same temperature & pressure contain equal numbers of particles Molar Volume – the volume of 1.0 mol of any gas at STP. Molar Volume – the volume of 1.0 mol of any gas at STP. At STP, one mole of any gas… At STP, one mole of any gas… 1 mol = 6.022 x 10 23 particles = Molar Mass in grams = 22.4 L THIS IS A REVIEW! We have already done this! THIS IS A REVIEW! We have already done this! –Use your dimensional analysis to solve these problems. Avogadro’s Principle

3. Example How many moles of CO 2 gas are in a 2.5 L flask at STP? How many moles of CO 2 gas are in a 2.5 L flask at STP? 2.5 L 1 mol =.11 moles CO 2 22.4 L 22.4 L How many atoms of He are present in a 1.75 L balloon at STP? How many atoms of He are present in a 1.75 L balloon at STP? 1.75 L 1 mole 6.022x10 23 atoms = 4.70x10 23 atoms 22.4 L 1 mole 22.4 L 1 mole

4. Gas Stoichiometry coefficients in balanced chemical equations represent number of: coefficients in balanced chemical equations represent number of: – moles of each substance – liters of gases, assuming pressure and temp. remain constant Example C 3 H 8 (g)+ 5 O 2 (g) 3 CO 2 (g)+ 4 H 2 O (g) 1 mol 5 mol 3 mol 4 mol 1 L 5 L 3 L 4 L

5. Volume–Volume problems use the balanced equation to find volume ratio use the balanced equation to find volume ratioExample If 1.78 L of oxygen reacts, what volume of nitrogen will be produced? 4 NH 3 (g) + 3 O 2 (g) 2 N 2 (g) + 6 H 2 O (l) 1.78 L O 2 2 L N 2 = 1.19 L N 2 3 L O 2 3 L O 2

6. Volume–Mass Problems Mass-volume problems in which we use 22.4 L/mol will only work if the gas you are using is at STP or the gas you are producing will be at STP conditions!! If you are not at STP: If you are not at STP: –uses both stoichiometry and ideal gas law to solve problem –assumes a single set of pressure and temp. conditions –to complete these problems, the following must be available: – a balanced equation – mass or volume of a reactant or product – pressure and temperature values

7. Example – AT STP Given 25 L of oxygen gas, how many grams of water can be produced? O 2 (g) + 2 H 2 (g) 2 H 2 O (l) O 2 (g) + 2 H 2 (g) 2 H 2 O (l) 25 L O 2 1 mol O 2 2 mol H 2 O 18 g H 2 O 22.4 L O 2 1 mol O 2 1 mol H 2 O 22.4 L O 2 1 mol O 2 1 mol H 2 O = 40. g H 2 O = 40. g H 2 O

8. Example – NOT AT STP When 89.5 g of As 2 S 3 is heated with excess oxygen, what volume of SO 2 is produced at 20 o C and 98.0 kPa? 2 As 2 S 3 (s) + 9 O 2 (g) 2 As 2 O 3 (s) + 6 SO 2 (g) convert g of given to mol of required substance convert g of given to mol of required substance As = 2 x 74.92 S = 3 x 32.00 246 g/mol 246 g/mol 89.5 g As 2 S 3 1 mol As 2 S 3 6 mol SO 2 = 1.09 mol 246 g As 2 S 3 2 mol As 2 S 3 SO 2 246 g As 2 S 3 2 mol As 2 S 3 SO 2

9. solve for volume, using PV=nRT solve for volume, using PV=nRT P = 98.0 kPa T = 20 o C + 273 = 293K n = 1.09 mol SO 2 R = 8.314 kPa·L/mol·K V= nRT P V = (1.09 mol)( 8.314 kPa·L /mol·K)(293K) (98.0 kPa) (98.0 kPa) = 27.1 L SO 2