Absolute zero
4 marks · NormalThe diagram shows a pressure gauge connected to a sealed rigid container filled with air. The container is placed in a cold room and the temperature is monitored.
State what is meant by absolute zero.
The initial temperature of the air is 15 °C. Calculate the temperature in Kelvin.
If the temperature falls to -40 °C, calculate the new temperature in Kelvin.
Explain why the pressure in the container decreases as the temperature falls, referencing ideas about energy of gas particles.
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(a) Absolute zero is the lowest possible temperature, at which particles have minimal energy and cannot get colder.
(b) 288 K
(c) 233 K
(d) Pressure decreases because the gas particles have less kinetic energy as the temperature falls. The particles move more slowly, so they hit the walls less often and with less force, causing a lower pressure.
Common mistakes: Using the wrong sign when converting temperatures; not referencing kinetic energy for pressure change.
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Defines absolute zero as the lowest possible temperature where particles have minimal energy.
B1 (b) · 1 mark · Correct conversion: 15 + 273 = 288 K.
B1 (c) · 1 mark · Correct conversion: -40 + 273 = 233 K.
B1 (d) · 1 mark · Explains decrease in pressure as due to lower kinetic energy, less frequent/forceful particle collisions with container walls.
Worked solution
a) Absolute zero is the lowest possible temperature; it is the point at which the particles of a substance have minimum energy and cannot be cooled further.
b) T = 15 + 273 = 288 K.
c) T = -40 + 273 = 233 K.
d) As temperature decreases, particles in the gas move more slowly because they have less kinetic energy. They collide with the walls of the container less frequently and with less force, so the pressure decreases.