Calculations with gases Calculations With Gases Objective: to know to use volumes of gases in equations Outcomes: be able to calculate amounts of substances (in mol) in reactions involving volume of gas These calculations may involve reactants and/or products. be able to calculate reacting volumes of gases from chemical
equations, and vice versa, using the concepts of amount of substance be able to calculate reacting volumes of gases from chemical equations, and vice versa, using the concepts of molar volume of gases Avogadros law In 1811 the Italian scientist Amedeo Avogadro developed a theory about the volume of gases.
Avogadros law: qual volumes of different gases at the same pressure and temperature will contain equal numbers of particles. For example, if there are 2 moles of O2 in 50 cm3 of oxygen gas, then there will be 2 moles of N2 in 50 cm3 of nitrogen gas and 2 moles of CO2 in 50 cm3 of carbon dioxide gas at the same temperature and pressure. Using this principle, the volume that a gas occupies will depend on the number of moles of the gas.
Calculations using reacting volumes of gases H2 (g) + Cl2 (g) 2HCl (g) 100 cm3 of hydrogen is mixed with 100 cm3 of chlorine, and reacted. What volume of hydrogen chloride is formed? The ratio in the equation is 1: 1 : 2 The answer is 200 cm3 Calculations using reacting volumes of gases
2SO2 (g) + O2 (g) 2SO3 (g) 200 cm3 of sulfur dioxide are mixed with 200 cm3 of oxygen and reacted. What volume of sulphur trioxide is formed? Ratio is 2: 1: 2 All of the sulfur will react but only half of the oxygen will react 200 cm3 of sulfur trioxide will be formed, but 100 cm3 of the oxygen will be left over.
Calculations using reacting volumes of gases 2N2O5 (g) O2 (g) + 4NO2 (g) Calculate the total volume of gas produced when 8.25 dm3 of dinitrogen pentoxide decomposes 2 moles of N2O5 produces 1 mole of O2 and 4 moles of NO2, which is 5 moles in total. (5/2) X 8.25 = 20.6 dm3
Molar volumes of gases If the temperature and pressure are fixed at convenient standard values, the molar volume of a gas can be determined. Standard temperature is 273 K (0oC) and pressure is 101.3 At standard temperature and kPa. pressure (s.t.p) 1 mole of any gas occupies a volume of 22.4 dm3. This is the molar gas volume. At room temperature and pressure (r.t.p) 1 mole of any gas will occupy a volume of 24 dm3 mol-1 . R. T.P is 293 K (20o C)
and 101.3 kPa. This is the molar gas volume. Number of moles = Volume in dm3 Molar gas volume At r.t.p. the molar gas volume is 24 dm3 mol-1 At s.t.p. the molar gas volume is 22.4 dm3 mol-1 Example
How many moles are there in 6.0 dm3 of oxygen at r.t.p.? Number of moles = 6.0 / 24 = 0.25 moles of oxygen molecules 1. What amount in moles of gas molecules are in 36 dm3 at r.t.p? 1.5 2. What is the
volume of 6 mol SO2 (g) at r.t.p? 3 144 dm 3 3. What is the
mass of 0.6 dm N2 at r.t.p? 0.7 g (use moles = volume/ molar gas constant, then moles =
molar mass / mass) 3 volume of 1.282 g SO (g) at r.t.p? 4. What the 0.48isdm (use moles = molar mass / mass, then volume = 2
moles x molar gas volume) Calculating Gas Volumes Using Molar Calculations How much gas is produced when 15 g of sodium is reacted with excess water at r.t.p? 2Na (s) + 2H2O (l) 2NaOH (aq) + H2 (g) M of Na = 23.0 g mol-1 so number of moles in 15 g of Na = 15/23.0 = 0.652 moles
Ratio Na : H2 = 2 : 1 so moles H2 = 0.652/2 = 0.326 Volume of H2 = moles x molar gas volumes = 0.326 x 24 = 7.8 dm3 Note the water is in excess so you know that all of AQA worksheet Workbook page 36 Measuring Molar Volumes Of Gases
You can find the volume of gas evolved in a reaction by collecting the gas that is produced in a gas syringe of by displacing water from a measuring cylinder. You can use experiments to work out the molar volume of a gas. Measuring the volume of gas given off. Measuring volume of gas produced
Example Calculations With Gases Objective: to know to use volumes of gases in equations Outcomes: be able to calculate amounts of substances (in mol) in reactions involving volume of gas These calculations may involve reactants and/or products.
be able to calculate reacting volumes of gases from chemical equations, and vice versa, using the concepts of amount of substance be able to calculate reacting volumes of gases from chemical equations, and vice versa, using the concepts of molar volume of gases
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