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Gas Volumes L.O.

Gas Volumes L.O. I can state three ways that gas can be collected quantitatively from an experiment. Amedeo Avogadro. Avogadro’s law. Avogadro’s law states that:. Equal volumes of gases, at the same temperature and pressure, contain the same number of molecules.

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Gas Volumes L.O.

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  1. Gas Volumes L.O. I can state three ways that gas can be collected quantitatively from an experiment.

  2. Amedeo Avogadro

  3. Avogadro’s law Avogadro’s law states that: Equal volumes of gases, at the same temperature and pressure, contain the same number of molecules. This means that one mole of any gas at a given temperature and pressure will always have the same volume. At room temperature and pressure (RTP), one mole of any gas has a volume of 24dm3 (24 litres). What would happen to the volume of a mole of gas if you: • increased the temperature? • increased the pressure?

  4. Gases and moles

  5. Gases and moles

  6. Gases and moles

  7. Gas calculations: example 1 Hydrogen gas reacts with oxygen gas to make water vapour. If 24dm3 of hydrogen gas is burned with excess oxygen, what volume of water vapour is produced? Step 1: Write a balanced equation for the reaction: • 2H2 (g) + O2 (g)  2H2O (g) Step 2: Turn volume of hydrogen into moles of hydrogen: volume 24 moles of H2 = = = 1 mole of H2 24 24 Step 3: Use the balanced equation to work out how many moles of water vapour you should make: 1 mole of hydrogen makes 1 mole of water vapour Step 4: Turn moles of water into volume of water vapour: volume = moles × 24 = 1 × 24 = 24 dm3 of water vapour

  8. Gas calculations: example 2 Nitrogen and hydrogen react together to make ammonia. What is the maximum volume of ammonia that can be made from 2,400cm3 of nitrogen gas? Step 1: Write a balanced equation for the reaction: N2 (g) + 3H2 (g)  2NH3 (g) Step 2: Turn volume of nitrogen into moles of nitrogen: volume moles of N2 = NOTE: To convert cm3 to dm3, divide by 1,000. 24 2.4 = 24 = 0.1 moles of N2

  9. Gas calculations: example 2 continued Step 3: Use the balanced equation to work out how many moles of ammonia you can make: 1 mole of N2 makes 2 moles of NH3, so 0.1 moles of N2 makes 0.2 moles of NH3. Step 4: Turn moles of ammonia into volume of ammonia: volume = moles × 24 = 0.2 × 24 = 4.8dm3 (4,800cm3) of ammonia

  10. Gas calculations

  11. Using gases to follow reactions Many chemical reactions produce gases. Scientists can measure how much gas is produced and use it to follow the progress of a reaction. The volume of gas produced can also be converted into moles and used to determine the amount of reactants present at the start of the reaction. Which gas is produced by each of these reactions? Magnesium + hydrochloric acid Calcium carbonate + hydrochloric acid Decomposition of hydrogen peroxide hydrogen carbon dioxide oxygen

  12. Measuring gases in reactions One way of measuring how much gas is produced in a reaction is to use an upturned measuring cylinder filled with water. As the gas bubbles into the measuring cylinder, it displaces the water. This technique works well for gases which are less dense than air and not very soluble in water. What would be the problem with using this method for a gas which is very soluble in water?

  13. Measuring gases in reactions Another method of collecting a gas is to use a gas syringe. This technique works well for all gases. What are the advantages and disadvantages of using a gas syringe rather than a measuring cylinder to collect the gas?

  14. Measuring gases in reactions One other method of measuring how much gas is produced in a reaction is to measure the mass of the reaction mixture. What will happen to the reading on the balance? Why is cotton wool placed in the top of the flask?

  15. Limiting reactants The amount of gas produced in a reaction will depend on thelimiting reactant. This is the reactant that runs out first, bringing the reaction to an end. time (s) volume H2 (cm3) The other reactant(s) are said to be “in excess”. This means that there will be some left after the reaction. 0 0 150 30 300 60 90 450 This table shows hydrogen gas production during a reaction between a small amount of magnesium and excess dilute hydrochloric acid. 120 600 150 700 180 780 210 850 240 895 270 910 After how many seconds was all the magnesium used up? 300 910

  16. Reaction graphs

  17. Following reactions using gases

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