RI 04 The Gaseous State (Suggested Ans)

1 Raffles Institution Year 5 H2 Chemistry 2024 Tutorial 4 – The Gaseous State (Suggested Answers for Discussion Questions) Discussion Questions 11 Mass of CO2 in 500 cm3 of saturated solution = 0.500 × 1.50 = 0.750 g Mass of CO2 released = 2.00 – 0.750 = 1.25 g Amount of CO2 released = 1.25/molar mass = 1.25/44.0 = 0.0284 mol Volume of CO2 released = 0.0284 × 24 = 0.682 dm3 = 682 cm3 12 (a) For a fixed amount of ideal gas at constant T, pV remains constant as p increases. (b) Using the ideal gas equation, pV = nRT 𝑉𝑉 = (0.40)(8.31)(300) 12.0 × 105 = 8.31 × 10-4 m3 = 0.831 dm3 (c) pressure, p / Pa volume, V / dm3 pressure x volume, pV / Pa dm3 5.0 × 105 1.924 9.62 × 105 10.0 × 105 0.926 9.26 × 105 15.0 × 105 0.592 8.88 × 105 When p = 12.0 × 105 Pa, estimated pV = 9.26 × 105 – 2 5 (9.26× 105 – 8.88 × 105) = 9.11 × 105 Pa dm3 When estimated 9.11 × 105 Pa dm3, V = 9.11 × 105 Pa dm3 ÷ 12.0 × 105 Pa = 0.759 dm3 (d) Value of V in (c) is smaller than that in (b). This implies that the gas occupies a volume smaller than what it would were it ideal. As the pressure exerted on the system is moderately high, the polar HCl gas molecules come closer together and the intermolecular attractive forces (id-id and pd-pd) between the HCl gas molecules become significant, causing the volume to be smaller than what it would were it ideal.

2 13 (a) 2 main assumptions are: • The gas particles exert negligible intermolecular attractive forces on one another. • The volume of gas particles is negligible compared to the volume of container. Reject: volume of gas is negligible (missing ‘particles’) Other assumptions: • The gas particles are in constant random motion. • Collision between gas particles are perfectly elastic. • The average kinetic energy of gas particles is proportional to absolute temperature. (b) 8.31pV RnT = = J K–1mol–1 (c) Under low pressure and high temperature • At low pressure, the gas particles are very far apart. Hence the volume of the gas particles can be considered negligible compared to the volume of the container. In addition, the intermolecular attractive forces between widely spaced gas particles are also negligible. • At high temperature, the gas particles possess sufficiently high kinetic energy to overcome the intermolecular attractive forces. Hence, the intermolecular attractive forces can be considered negligible. (d) At moderately high pressure: • O 2 molecules come closer together and the intermolecular attractive forces between O 2 molecules become significant. This causes the gas to occupy a volume smaller than that of an ideal gas. This results in a smaller V and pV/nT < 8.31 (negative deviation). A t very high pressure: • The v olume of the system becomes very small. Thus, the volume occupied by the O2 molecules bec