The gas laws
2 marks · EasyExplain, using the idea of molecules, why the pressure of a gas increases if it is heated at constant volume.
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Heating increases the speed of the molecules, causing them to hit the walls more often and with more force, which increases the pressure.
Also accept: The molecules move faster, collide more frequently and with greater force, increasing pressure.
Common mistakes: Saying only that molecules move faster, but not relating to collisions or pressure increase
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Marking points
B1 · 1 mark · Explains increased speed of molecules with temperature
B2 · 1 mark · Relates increased speed to more frequent or harder collisions causing greater pressure
Worked solution
When a gas is heated, the molecules gain kinetic energy and move faster. At constant volume, this means they collide with the container walls more frequently and with more force, increasing the pressure.