# Why is the Specific Heat of Helium 36 times greater than Xenon?

Given that these are single atoms, why should the specific heat difference be so great? And more specifically, why does it take 36 times as much energy to raise the temperature of a given mass of Helium compared to Xenon?

• How does it compare on a per-mole basis? – Jon Custer Mar 25 '15 at 13:44

• Err ... "Intuitively, temperature equals velocity" Is wrong two ways. First, temperature is proportional to the energy not the velocity, and secondly it is the average energy per mode, not the total (which should be very clear because total energy is extensive and temperature is intensive). So for a change in energy $\Delta E$ the temperature change is proportional to $\Delta E/N$ where $N$ is the number of modes (which reduces to the number of atoms for an ideal gas). – dmckee --- ex-moderator kitten Mar 25 '15 at 16:44
• In an ideal gas atoms have three degrees of freedom, the $x$, $y$ and $z$ directions, and each DOF gets about $\tfrac{1}{2}kT$ of energy. So the total internal energy is $\tfrac{3}{2}kT$ times the number of atoms. – John Rennie Mar 25 '15 at 16:54