# Thermal Physics, work done / internal energy helpWatch

Announcements
#1
Hey! I do CAIE exam board and I'm struggling in No. 2 of this paper https://papers.gceguide.xyz/A%20Leve..._w18_qp_41.pdf

Can someone help me with answering the table? I really don't know how to do it Thank you!
0
1 week ago
#2
(Original post by mygjjgknj)
Hey! I do CAIE exam board and I'm struggling in No. 2 of this paper https://papers.gceguide.xyz/A%20Leve..._w18_qp_41.pdf

Can someone help me with answering the table? I really don't know how to do it Thank you!
Hi, I am not sure why the helper deleted the post. If you still need help on the question, let me know. I would provide some explanation.
0
#3
(Original post by Eimmanuel)
Hi, I am not sure why the helper deleted the post. If you still need help on the question, let me know. I would provide some explanation.
hello! yes please! here's what i think i know, please tell me if i'm correct.

for P->Q, work done on gas is 0 because volume doesnt change. since delta U = W + Q, therefore increase in internal energy is +97.0 + 0 = +97.0 J

for Q->R, U=W + Q so U = -42.5 + 0 = -42.5 J

i don't know how to find for R->P though, i found that solving it like hess' law from chemistry gives the right answer, but is there another way to do it?
0
1 week ago
#4
(Original post by mygjjgknj)
Hey! I do CAIE exam board and I'm struggling in No. 2 of this paper https://papers.gceguide.xyz/A%20Leve..._w18_qp_41.pdf

Can someone help me with answering the table? I really don't know how to do it Thank you!
(Original post by mygjjgknj)
hello! yes please! here's what i think i know, please tell me if i'm correct.

for P->Q, work done on gas is 0 because volume doesnt change. since delta U = W + Q, therefore increase in internal energy is +97.0 + 0 = +97.0 J

for Q->R, U=W + Q so U = -42.5 + 0 = -42.5 J

i don't know how to find for R->P though, i found that solving it like hess' law from chemistry gives the right answer, but is there another way to do it?

Hi, thank for the reply. Your answer and explanation for the change P→Q and Q→R is correct.

As for the change R→P, you need to make use your answer for 2(b)(i), the total change in internal energy of the gas during the complete cycle PQRP is zero.

Using this info, you can find the increase in internal energy of gas for the change R→P.

Then apply the first law of thermodynamics
ΔU = Q + W
for the change R→P to find thermal energy transferred to gas.
0
#5
(Original post by Eimmanuel)
Hi, thank for the reply. Your answer and explanation for the change P→Q and Q→R is correct.

As for the change R→P, you need to make use your answer for 2(b)(i), the total change in internal energy of the gas during the complete cycle PQRP is zero.

Using this info, you can find the increase in internal energy of gas for the change R→P.

Then apply the first law of thermodynamics
ΔU = Q + W
for the change R→P to find thermal energy transferred to gas.
so since internal energy of P->Q is 97.0, and Q->R is -47.5, we have 97.0 + (-42.5) = 54.5 J, but since total internal energy is 0, then internal energy of R->P would have to be -54.5 J yes?
0
1 week ago
#6
(Original post by mygjjgknj)
so since internal energy of P->Q is 97.0, and Q->R is -47.5, we have 97.0 + (-42.5) = 54.5 J, but since total internal energy is 0, then internal energy of R->P would have to be -54.5 J yes?
Correct.
0
#7
(Original post by Eimmanuel)
Correct.
okay thank you very much !!
0
X

new posts
Back
to top
Latest
My Feed

### Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

### See more of what you like onThe Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

### University open days

• De Montfort University
Sat, 7 Dec '19
• Buckinghamshire New University
Sat, 7 Dec '19
• Regent's University London
Sat, 7 Dec '19

### Poll

Join the discussion

#### Which party will you be voting for in the General Election?

Conservatives (81)
19.38%
Labour (204)
48.8%
Liberal Democrats (57)
13.64%
Green Party (26)
6.22%
Brexit Party (5)
1.2%
Independent Group for Change (Change UK) (3)
0.72%
SNP (8)
1.91%
Plaid Cymru (3)
0.72%
Democratic Unionist Party (DUP) (0)
0%
Sinn Fein (6)
1.44%
SDLP (0)
0%
Ulster Unionist (2)
0.48%
UKIP (6)
1.44%
Other (2)
0.48%
None (15)
3.59%