How to do this chemistry problem with gases?

Chemistry help please?!?

• Hi guys I'm really stressed about my chemistry test tomorrow. My teacher gave us a study guide but no answers to it. Id really appreciate it! thanks!:) 2. What is true at STP? Temperature is 300 Kelvin. One mole of gas occupies a volume of 22.4 liters. Pressure is 101 atmospheres. Volume is 24 liters. Multiple Choice 3. Under certain conditions, neon (Ne) gas diffuses at a rate of 7.0 centimeters per second. Under the same conditions, an unknown gas diffuses at a rate of 4.9 centimeters per second. What is the approximate molar mass of the unknown gas? 6.5 g/mol 11 g/mol 20 g/mol 41 g/mol Multiple Choice 4. Which of the following gases will have the highest velocity at a given temperature? Ne O2 He Cl2 Multiple Choice 5. If 5.0 liters of carbon dioxide gas are produced by the reaction below at STP, how many liters of oxygen gas were used in the reaction? 2 CO (g) + O2 (g) 2 CO2 (g) 10.0 L 7.5 L 5.0 L 2.5 L 6. How many grams of chlorine gas (Cl2) are in a 17.8 liter sample at 1.1 atmospheres and 29°C? Show all work used to solve this problem. 7. How many liters of water vapor can be produced if 8.9 liters of methane gas (CH4) are combusted, if all measurements are taken at the same temperature and pressure? Show all of the work used to solve this problem. CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (g) 8. How many liters of oxygen gas, at standard temperature and pressure, will react with 25.0 grams of magnesium metal? Show all of the work used to solve this problem. 2 Mg + O2 2 MgO 9. If 24.6 grams of lithium react with excess water, how many liters of hydrogen gas can be produced at 301 Kelvin and 1.01 atmospheres? Show all of the work used to solve this problem. 2 Li (s) + 2 H2O (l) 2 LiOH (aq) + H2 (g)

• Answer:

  2. 22.4 L / mol at STP pressure 101.3 kPa 3? 4. the lightest gas 5. the ratio of O2 to CO2 is 1 to 2. So if you produce 5 of CO2 you will need 2.5 of O2 6. You need to use PV = nRT and solve for n . n = PV / RT Just plug in the numbers and solve. Once you have n you convert to mass by using mass = moles x molar mass 7. Assume STP conditions. so 8.9 L of CH4 is 8.9 / 22.4 L/mol = 0.397 moles water vapor is produced at twice the number of moles so moles of water will be 0.397 x 2 = 0.795 Liters = moles x 22.4 which equals 0.795 mol x 22.4 = 17.8 L 8. Do the same thing here. convert the Mg into moles. Notice the mole ratio is 2 to 1. So you only need 1/2 the moles of O2 as you calculate for the Mg. The multiply like I did in question 7 to find liters. 9. Convert eh mass of Li into moles. Then multiply by 1/2 because you only produce 1/2 that number of moles of H2 as you have of Li Then use PV = nRT to solve for V. V = nRT / P