Cv vs. Cp [ENDORSED]

[Miranda 1J]

Can someone please explain when we use Cv and when we use Cp and how we would know which one to use? Also, what's the difference between DH= nCpDT and DH= gCspDT? Does it matter which one we use?

Thanks!

[SPandya1F]

Use Cv when there's constant volume. This is the specific heat when there's constant volume.
Use Cp when there's constant pressure. This is the specific heat when there's constant pressure.

[Clarisse Wikstrom 1H]

Cv is the molar heat capacity of a gas @ CONSTANT VOLUME, whereas Cp is the molar heat capacity of a gas at CONSTANT PRESSURE. In one example (#31), you would use it when doing q=mCdeltaT if you're given an ideal gas but no molar heat capacity. The Cp and Cv for ideal gases can be found on Lavelle's equation sheet on his website.

[Julian Krzysiak 2K]

Cp is the heat capacity for something at a constant pressure, and would be equal to
Cv is the heat capacity for something at a constant volume, and would be equal to
You'll know when to use a particular heat capacity because they'll specify in the problem the conditions of the reaction, or you'll have to infer the conditions, for example, when there is an open container, it will have to be at a constant pressure of 1atm.
You usually use these equations when dealing with anything in calculating how much heat was given off, the change in temperature, or any variation in dealing with


is the specific heat capacity for something at a constant pressure in terms of moles
is the specific heat capacity for something at a constant pressure in terms of grams
So you'll have to use either one depending in which units they give the amount to you, or if given enough information, you could convert grams into moles, vice versa, and then use which equation you want.

[AlyssaPeckham1A]

Also to solve for the values of Cvm and Cpm you can use the equations Cvm=3/2*R and Cpm=5/2*R for the molar heat capacity.

[Katelyn 2E]

Will we have to know the Cvm and Cpm values for the test?

[Lucia H 2L]

They are listed on the formula sheet!
Ideal gas, Cp = (5/2)R
Ideal gas, Cv = (3/2)R
Both are constant because heat capacity for gases isn't dependent on temp or volume.

[Justin Bui 2L]

We would also be told the conditions of the problem and then we would know which one to use, Cp or Cv, based off of that.

[Guadalupe T 1E]

The problem usually states when there is constant pressure/volume

[Warda Sahib 2J]

Cv-is when there's constant volume and Cp-is when there's constant pressure.

[Abby Ellstrom 1I]

Cv is when the volume is constant and Cp is when the pressure is constant.

[Kenan Kherallah 2C]

Whats R?

[Brian Chang 2H]

Cv is for constant volume.
Cp is for constant pressure.

[Jeannine 1I]

Whats R?

I believe R refers to the universal gas constant!