Gas calculations

• What is the equation that links the volume of a gas to the number of moles of that gas?

  Volume = moles × 24
• Why does the equation for gas volume apply to any type of gas?

  Because the relationship between moles and volume is consistent for all gases at room temperature and pressure
• How do you calculate the volume of 3.5 moles of chlorine gas?

  Multiply 3.5 by 24 to get 84 decimeters cubed
• If you have 60 decimeters cubed of oxygen, how many moles do you have?

  60 divided by 24 equals 2.5 moles
• What is the first step to find the volume of 27 grams of water vapor?

  You need to find the number of moles first
• What is the relative formula mass (Mr) of water (H2O)?

  18
• How do you find the number of moles from the mass of water vapor?

  Divide the mass (27 grams) by the Mr (18)
• What is the volume of 1.5 moles of water vapor?

  1. 5 multiplied by 24 equals 36 decimeters cubed
• What does it mean when hydrogen is in excess in a reaction?

  It means that hydrogen will not limit the amount of product formed
• How do you find the moles of nitrogen from its volume of 18 decimeters cubed?

  Divide 18 by 24 to get 0.75 moles
• How do you determine the moles of ammonia produced from nitrogen?

  Use the molar ratio from the balanced equation
• If the molar ratio of nitrogen to ammonia is 1:2, how many moles of ammonia are produced from 0.75 moles of nitrogen?

  0.75 times 2 equals 1.5 moles of ammonia
• What is the volume of 1.5 moles of ammonia?

  1. 5 multiplied by 24 equals 36 decimeters cubed
• Why can you directly multiply the volume of nitrogen by the molar ratio when converting gas volumes?

  Because gas volumes are directly proportional to the number of moles
• If you start with 4 decimeters cubed of nitrogen, how much hydrogen would it react with?

  Multiply 4 by 3 to get 12 decimeters cubed of hydrogen
• Under what conditions does the equation with the number 24 apply?


  At room temperature and pressure
• What happens to gas volumes if temperature or pressure changes?

  The volume of gases will change with different temperatures or pressures
• What is the only equation you need to use in exams for gas volumes?

  The equation with the number 24