# Thermal Processes

[SOLVED] Thermal Processes

## Homework Statement

With the pressure held constant at 240 kPa , 42 mol of a monatomic ideal gas expands from an initial volume of 0.75 meters cubed to a final volume of 2.0 meters cubed.

a)How much work is done by the gas during expansion?
b)What were the initial and final temperatures?
c)what was the change in the internal energy of the gas?

I know the anwser for a) is 3.0*10^5
i cant find the other three

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Chi Meson
Homework Helper
i cant find the other three
Where have you looked?

Andrew Mason
Homework Helper

## Homework Statement

With the pressure held constant at 240 kPa , 42 mol of a monatomic ideal gas expands from an initial volume of 0.75 meters cubed to a final volume of 2.0 meters cubed.

a)How much work is done by the gas during expansion?
b)What were the initial and final temperatures?
Use ideal gas law: PV = nRT. You know P, V and n so just work out T for intial and final states.
c)what was the change in the internal energy of the gas?
What is Cv for a monatomic gas? How is $\Delta U$ related to Cv and $\Delta T$?
Use first law: dQ = dU + dW

As a short-cut, since it is a constant pressure process, you can just use: dQ = CpdT. What is Cp for a monatomic gas?

I know the anwser for a) is 3.0*10^5
Units?

AM

the units for the first answer are Joules

How do i wotk out the T for inital and final states

the Cv for a monatomic gas is 12.465

delta U is 3/2*n*R*deltaT

Cp for a monatomic gas is 20.775

hage567
Homework Helper
the units for the first answer are Joules

How do i wotk out the T for inital and final states
Use the ideal gas law PV=nRT like Andrew suggested in post #3. You were given all the information you need to solve this for T.

For T i get 859.5 How do i get the inital temperature

hage567
Homework Helper
You just use the ideal gas law twice. Once for the initial state (so before it expands), and once for the final state (after it expands).

Be very careful with your units.