What is the total motional contribution to the molar internal energy of gaseous BF3?

Question

What is the total motional contribution to the molar internal energy of gaseous BF3?

1. 3RT
2. RT
3. 1.5RT
4. 3.5 RT
5. 2.5RT

For reaction in which gases are neither produced nor consumed, change in heat is...
1. less than change in energy
2. the same as change in energy
3. unrelated to change in energy
4. greater than change in energy

Answer 1

I found this question confusing, but think that the expression "total motional contribution" is probably just be a confusing way of saying "contribution of kinetic energy". Or just possibly it also includes rotational energy, depending on the exact definition being used in your textbook. Either way, you can work out the answer by using the principle that each classical degree of freedom gives you 0.5RT energy.

For the second question, you are being invited to use the equation

DeltaE = q + w

If gases are neither produced nor consumed, is any work being done? What does that tell you about the relationship between q, the change in heat, and DeltaE, the change energy?

Good luck!