Three identical 10 L, tanks contain 6 mol of helium (He) at 293 K. The pressure in each of the tanks is increased as described below Tank A The tank volume is decreased from 10 L to 5 L while the temperature and the number of moles of He remain constant. Tank B: The tank temperature is increased from 293 K to 308 K while the volume and the number of moles of He remain constant. Tank C: The number of moles of He in the tank is increased from 6 mol to 9 mol while the temperature and the volume remain constant. How is the average kinetic energy, KE, of the He gas affected in each case? Drag each item to the appropriate bin.
We will assume the He gas in all the three tanks behave as an ideal gas. The average kinetic energy of an ideal gas is directly proportional to the absolute temperature of the system. The relation is given as
KEavg = 3kT/2 where k = R/NA is the Boltzmann constant.
From the above relation, it is clear that the average kinetic energy of an ideal gas depends only on the temperature. Hence, the average kinetic energy of He gas in tanks A and C will remain unchanged, since the temperature of the system stays constant. The temperature of tank B is increased and hence the average kinetic energy of He in tank B will increase.