Calculate the heat capacity at constant volume and constant pressure.

In summary, the student attempted to solve a homework question that was unclear, and was given confusing instructions by their professor.
  • #1
LogicX
181
1

Homework Statement



I am given the amount of moles of gas, how many joules of heat I put into the system, and a positive change in temperature. Then it says "calculate the molar heat capacities at constant volume and constant pressure of the gas."

Homework Equations



q=CT, C(constant pressure)-C(constant volume)=nR, U= q+w, H=U+PV

The Attempt at a Solution



I just don't know how to do this problem without knowing whether the temperature change occurs at constant volume or constant pressure. If I knew either of those the problem would be easy.

I have q and delta(T), so I should be able to calculate a heat capacity. But I don't know which one it would be.
 
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  • #2
Can you give exact wording of the question? Perhaps the information is there, just hidden?
 
  • #3
"When 178 J of energy is supplied as heat to 1.9 mol of gas molecules, the temperature of the sample increases by 2.55 K. Calculate the molar heat capacities at constant volume and constant pressure of the gas."
 
  • #4
Nah, you are right - question is unclear.
 
  • #5
Borek said:
Nah, you are right - question is unclear.

Ok thanks, I'll go talk to my professor tomorrow.
 
  • #6
Well my professor is a senile old man so I tried to ask him today, but he seemed to have a mental block against admitting he wrote the question wrong so at first he tried to tell me I can assume the pressure is constant, then that I can assume that the volume is constant.

I guess I just have to hope that he doesn't pull this **** on the exam because he would probably just arbitrarily pick one that he wanted us to assume was constant and if I confronted him about it get the same talking in circles answer that I got just now.

I hate college sometimes.
 

What is heat capacity and why is it important?

Heat capacity is a measure of the amount of heat energy required to raise the temperature of a substance by a certain amount. It is important because it helps us understand how different materials respond to changes in temperature and how much energy is needed to maintain a stable temperature.

What is the difference between heat capacity at constant volume and constant pressure?

Heat capacity at constant volume is the amount of heat energy required to raise the temperature of a substance while keeping its volume constant. Heat capacity at constant pressure is the amount of heat energy required to raise the temperature of a substance while allowing it to expand. This expansion allows for some of the heat energy to be used in the work of pushing against the surrounding pressure.

How do you calculate the heat capacity at constant volume?

The heat capacity at constant volume can be calculated by taking the derivative of the internal energy with respect to temperature, keeping the volume constant. This gives the equation CV = (∂U/∂T)V, where CV is the heat capacity at constant volume and U is the internal energy.

How do you calculate the heat capacity at constant pressure?

The heat capacity at constant pressure can be calculated by taking the derivative of the enthalpy with respect to temperature, keeping the pressure constant. This gives the equation CP = (∂H/∂T)P, where CP is the heat capacity at constant pressure and H is the enthalpy.

What factors can affect the heat capacity of a substance?

The heat capacity of a substance can be affected by several factors such as the type of material, its phase (solid, liquid, gas), temperature, and pressure. It can also be influenced by the presence of impurities or additives in the substance. Additionally, the heat capacity can vary depending on whether the substance is measured at constant volume or constant pressure.

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