• Support PF! Buy your school textbooks, materials and every day products Here!

Thermal Processes

  • Thread starter HELLO11
  • Start date
19
0
[SOLVED] Thermal Processes

1. 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?
d)How much heat was added?

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

can someone please help
 

Answers and Replies

Chi Meson
Science Advisor
Homework Helper
1,766
10
Andrew Mason
Science Advisor
Homework Helper
7,540
317
1. 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 [itex]\Delta U[/itex] related to Cv and [itex]\Delta T[/itex]?
d)How much heat was added?
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
 
19
0
the units for the first answer are Joules

How do i wotk out the T for inital and final states
 
19
0
the Cv for a monatomic gas is 12.465

delta U is 3/2*n*R*deltaT
 
19
0
Cp for a monatomic gas is 20.775
 
hage567
Homework Helper
1,509
1
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.
 
19
0
For T i get 859.5 How do i get the inital temperature
 
hage567
Homework Helper
1,509
1
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.
 
19
0
thanks for all your help
 

Related Threads for: Thermal Processes

  • Last Post
Replies
1
Views
1K
  • Last Post
Replies
1
Views
1K
  • Last Post
Replies
4
Views
2K
  • Last Post
Replies
5
Views
3K
  • Last Post
Replies
4
Views
2K
Replies
4
Views
1K
Replies
8
Views
2K
Top