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Reviewed CSCA Physics question · Easy

In a container of ideal gas, the absolute temperature is increased from 300 K to 900 K while the number of molecules and the volume remain constant. What happens to the average translational kinetic energy of a single molecule?

  1. It becomes one third of its original value.
  2. It becomes three times its original value.
  3. It becomes nine times its original value.
  4. It remains the same.
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Correct answer

B. It becomes three times its original value.

Principle or equation

The average translational kinetic energy of an ideal gas molecule is directly proportional to the absolute temperature: KE_avg = (3/2)kT.

Why this answer is correct

Since KE_avg is proportional to T, tripling the absolute temperature (300 K to 900 K) triples the average kinetic energy.

Example

If at 300 K the average kinetic energy is 6.21e-21 J, at 900 K it becomes 1.863e-20 J.

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