Explain why CCl4(g) will have more energy than Ar(s) if both gases are heated simultaneously.?

Question

TOPIC: Enthalpy

Answer 1

The equipartition theorem says that the energy will be distributed evenly among all the modes available.

For Ar, the only place to put in energy is in translational motion, because there can be no vibrations w/ just one atom, and rotation of an atom doesn't store energy either (actually it's more like an electronic transition, but that's another story. Just approximate an atom as a geometric point, and there is no energy in rotation.)

For CCl4, the energy can be distributed among vibrations and rotations of the molecule, as well as the translation of the molecule. The total number of modes =3A, where A is the number of atoms. For CCl4, 5 atoms means 15 modes (3 translation which are equivalent, 3 rotation which happen to be equivalent b/c of the symmetry of CCl4 assuming all the same Cl isotope, and 9 vibration).

Now, back to the equipartion theorem and temperature. Temp is a meausre of the average translational energy. So, the translational energy of Ar and CCl4 will be the same at a given temperature (the average velocity of the CCl4 will be less b/c it's heaver) But to get there, you had to put in more energy into the CCl4, b/c other modes took energy along the way.

Answer 2

I believe it has to do with the breaking of bonds in the CCl4. Since the C - Cl bond is extremely strong, it takes a great deal of energy to break it. Ar on the other hand has no such bonds to break, so if they are heated to the same temperature, CCl4 should have a higher enthalpy. I may be wrong though, I haven't taken chem in a number of years.

Answer 3

because CCI4 is smarter it doesn't want to get burned