# Molar heat capacity at constant pressure/volume

• Nick Jarvis
In summary, the conversation is about calculating the molar heat capacities of an ideal gas at constant pressure and volume. The energy supplied to 2.0 moles of gas was 117J, resulting in a temperature change of 2.0K. The individual then asks for help in solving the problem, realizing that they need to know the value of R and questioning their understanding of the formula for molar heat capacity. Another person points out that they should know R and clarifies that they cannot use n=2. The conversation ends with the individual thanking the other person for their help and acknowledging their need to revisit the module.
Nick Jarvis
Morning

I am being stupid but cannot work out these problems:

1. Energy supplied to 2.0 moles of an ideal gas is 117J and it changes the temperature by 2.0K (at constant pressure).
2. Calculate both molar heat capacities at constant P and V.3. Firstly, I divided 117J by 4 to get the energy required to change 1 mole by 1k. Answer was 29.25J/m/K. Seems way too simple? Then, I have:

Cp = Cv + nR, as we know that Cp is usually higher. So 29.25J/m/K = Cv + nR

I know n = 2.0 moles, but the question doesn't give R. Or should I know R? Or am I completely wrong?

Sorry if this is a basic question.

Cheers

Nick

Yes, you are expected to know R. By the way, you weren't going to use n = 2, were you?

Nick Jarvis
Thank-you mjc

And yes, I was. Cheers for the heads up. I didn't spend enough time on this module so trying now to catch up. I will revisit it and find out what n refers to.
Cheers again :)

## 1. What is molar heat capacity at constant pressure/volume?

Molar heat capacity at constant pressure/volume is the amount of heat required to raise the temperature of one mole of a substance by one degree Celsius while keeping the pressure or volume constant.

## 2. What is the difference between molar heat capacity at constant pressure and constant volume?

Molar heat capacity at constant pressure refers to the heat required to raise the temperature of a substance while keeping the pressure constant. Molar heat capacity at constant volume, on the other hand, refers to the heat required to raise the temperature of a substance while keeping the volume constant.

## 3. How is molar heat capacity at constant pressure/volume measured?

Molar heat capacity at constant pressure/volume is typically measured using calorimetry, which involves measuring the change in temperature of a substance when a known amount of heat is added or removed.

## 4. What factors affect the molar heat capacity at constant pressure/volume?

The molar heat capacity at constant pressure/volume is affected by several factors, including the type of substance, its molecular structure, and the temperature at which the measurement is taken.

## 5. Why is molar heat capacity at constant pressure/volume important in thermodynamics?

Molar heat capacity at constant pressure/volume is an important concept in thermodynamics because it helps us understand how much heat is required to change the temperature of a substance. This information is vital in determining the energy and work involved in various chemical reactions and processes.

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