Homework 8.29: Need Clarification [ENDORSED]

[Vincent Tse 2B]

Hello,

I am unsure about the concept(s) behind the following problem:

8.29
Which molecular substance do you expect to have the
higher molar heat capacity, NO or NO2? Why?

Can someone please explain how to approach and answer this problem?

Thanks!

[Manpreet Singh 1N]

Hello,

My logic may be wrong, but the units for molar heat capacity are J*K^-1*mol^-1. I remember Professor Lavelle saying that the more mass something has the more the heat capacity. So since NO2 has one more oxygen (one more atom), there are more bonds that can absorb the energy that is added.

Hope that helps :)

[Athena Dong 2A]

In addition, section 8.10 of the book states that molar heat capacity increases with a molecule's complexity.

The molar heat capacity ( Cm ) of a nonlinear molecule is greater than that of a linear molecule, because a nonlinear molecule can rotate more ( around more axes ). Gases composed of molecules can store energy as both rotational kinetic energy ( KE due to rotational motion ) and translational kinetic energy ( KE due to motion through space ). For a linear molecule, the rotational contribution is less than that of a nonlinear molecule, so the total Cm ( for a given change in temperature ) of a linear molecule is less than that of a nonlinear molecule.
If we consider the molecular geometry of NO and NO2, we find that NO is linear, while NO2 is bent ( nonlinear ). Therefore, the Cm of NO2 should be greater than that of NO.

[[ I'm sorry for any typos!! Hopefully it's not too confusing :s ]]

[Hue_Vo_1D]

Generally, the main concept of this question is that the heat capacity increases with molecular complexity

-As more atoms are present in the molecule, there are more possible bond vibrations that can absorb added energy-(NO2 has one more oxygen atom compared to NO)