CHEMISTRY · Multi-part · A Level · Chemistry · Amount of substance · Amount of substance
Problem
Two ideal gases, CH₄(g) and C₂H₆(g), are placed together in a cylinder fitted with a frictionless, movable piston. Initially the piston is locked in place so that the volume is 10.0 L, the temperature is 300 K, and the mixture contains 2.00 mol CH₄(g) and 3.00 mol C₂H₆(g). After the initial measurement the piston is released, and the cylinder is slowly heated to 450 K. The system is allowed to expand until the total pressure returns exactly to the initial value.
(a) Calculate the initial total pressure inside the cylinder.
(b) Determine the final volume of the gas mixture once the total pressure has returned to its initial value at 450 K.
(c) Calculate the partial pressure of C₂H₆(g) after the expansion is complete.
(d) Explain whether the mole fraction of CH₄(g) changes during the heating and expansion process, and justify your answer.