Physics Grade 10 Gas laws Ideal gas law Formative assessment

Formative assessment

Cambridge 9702_s05_qp_4              Q2

(a) State what is meant by an ideal gas.                                                                                                        [2]

(b) The product of pressure p and volume V of an ideal gas of density ρ at temperature T is given by the expressions

                                  and                                                

where N is the number of molecules and k is the Boltzmann constant.

(i) State the meaning of the symbol <c²>.                                                                                                        [1]

(ii) Deduce that the mean kinetic energy EK of the molecules of an ideal gas is given by the expression

                                                                                                                                                      [2]

(c) In order for an atom to escape completely from the Earth’s gravitational field, it must have a speed of approximately 1.1 × 10⁴ m s^–1 at the top of the Earth’s atmosphere.

(i) Estimate the temperature at the top of the atmosphere such that helium, assumed to be an ideal gas, could escape from the Earth. The mass of a helium atom is 6.6 × 10^–27 kg.                                                                  [2]

(ii) Suggest why some helium atoms will escape at temperatures below that calculated  in (i).                          [1]