Ideal Gas Molecules
5 marks · NormalThe graph below shows how the pressure of a fixed mass of gas at constant volume varies with temperature:
Determine the temperature at which the pressure of the gas would reach zero according to the graph.
Explain what this value represents physically, and how it is linked to the kinetic energy of the gas molecules.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) -273 °C · must show extrapolation to where line crosses x-axis
(b) This temperature is called absolute zero. It represents the temperature at which the gas molecules have zero kinetic energy, so they are not moving and exert no pressure on the walls. It is the lowest temperature possible. · must show definition of absolute zero, reference to zero kinetic energy
Common mistakes: Misreading where the graph crosses the axis
Show mark scheme and worked solution
Marking points
B1 (a) · 2 marks · Accurately extrapolates graph to find temperature where p = 0: -273°C.
B2 (b) · 1 mark · States this temperature is absolute zero.
B3 (b) · 1 mark · Explains that at absolute zero, molecular kinetic energy is zero.
B4 (b) · 1 mark · States that no pressure is exerted, as molecules no longer move.
Worked solution
(a) The line crosses the temperature axis at -273°C.
(b) This value, -273°C, is known as absolute zero. It is the lowest possible temperature, where the gas molecules have no kinetic energy and stop moving, resulting in zero pressure.