My book has a question asking to calculate average kinetic energy of the molecules in 8g of methane.
By the Equipartition theorem, I calculated that energy:
1. per molecule per degree of freedom = $(1/2)kT$ (by definition)
2. per molecule = $3kT$ (since methane is polyatomic => 6 degrees of freedom
3. per mole = $3RT$
4. for 8g methane ($=0.5$ moles) = $1.5\cdot RT$
But the answer stated by my book is $0.75\cdot RT$ - just half of what mine is.
This is not the only question where values have mismatched. I have started losing faith from Equipartition theorem.
What did I get wrong?
SUMMARY+UPDATE: Final conclusion reached is that while total kinetic energy is indeed the one Equipartition theorem gives (and so it's correct! :D) but the textbook assumes the molecule to be at at very low temperatures (although this is NOT mentioned) implying the rotational and vibrational energies are NOT counted.
*=>my textbook says so. I understand that there's a lot of complex things in this topic, but let's please assume it is 6 as my book says.