## 8.31 HW problem

Rachel_Harland_3I
Posts: 19
Joined: Fri Jul 22, 2016 3:00 am

### 8.31 HW problem

I don't understand the formula the book used to solve this question... can someone try to explain this one to me?

Calculate the heat released by 5.025 g of Kr(g) at 0.400 atm as it cools from 97.6C to 25.0C at a) a constant pressure and b) a constant volume

Thanks !

Jessie_Chen_2L
Posts: 20
Joined: Wed Sep 21, 2016 2:59 pm

### Re: 8.31 HW problem

For part a, the molar heat capacity of a monatomic ideal gas at constant pressure, like Kr(g), is CP,m = (5/2)R.
To calculate the heat that is released, we use q = nCP,m(Tfinal-Tinitial) to get -90.6J. We have all the information because we can convert the gas to the amount of moles of gas and we have the molar heat capacity from the first equation and the final and initial temperature.
For part b, we do the exact same thing, except to find the molar heat capacity of a monatomic ideal gas at constant volume is CV,m = (3/2)R. Then the answer we get is -54.4J

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