## Heat Capacity at Constant Volume and Pressure

David Sarkissian 1K
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### Heat Capacity at Constant Volume and Pressure

I'm having a hard time distinguishing which constants to use in the correct situations. When do we use $\frac{3}{2}R$R, $\frac{5}{2}R$, $\frac{7}{2}R$, 3R, and 4R? Are there certain ones we can ignore because they never come up, or could we be asked to use any of them on our exam?

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### Re: Heat Capacity at Constant Volume and Pressure

we use 3/2 when working with monoatomic molecule like Ne and constant volume and 5/2 for a monoatomic molecule constant pressure. Add 1 to both of them when using a diatomic molecule like H2. We don't need to know anything past monoatomic molecules on the test

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### Re: Heat Capacity at Constant Volume and Pressure

Also, an additional tip to help you better understand which relation to use is knowing the relationship between Cp,m and Cv,m: Cp,m= Cv,m + R. Keeping in mind that molar heat capacity increases with molecular complexity, and knowing that you simply have to add R to the molar head capacity at constant volume to find molar heat capacity at constant pressure will help you remember what relation to use.