You are Here: Home >< Physics

# Which of the following statements about internal energy is/are true

Announcements Posted on
Would YOU be put off a uni with a high crime rate? First 50 to have their say get a £5 Amazon voucher! 27-10-2016
1. I) The internal energy is the sum of the Kinetic and Potential Energies of the molecules of the system
II) The internal energy of the system is proportional to temperature of the system
III) A change of phase does NOT affect the internal energy of the system because it happens at a constant temperature

I am thinking I and II are true
because
I is basically the definition of internal energy
II - internal energy=kinetic energy + potential energy. Since kinetic energy is proportional to kinetic energy, then internal energy will also be proportional to temperature

I am unsure about these though. Can someone let me know if I am correct or provide me with a correct solution
Thanks
2. (Original post by ksrw395)
I) The internal energy is the sum of the Kinetic and Potential Energies of the molecules of the system
II) The internal energy of the system is proportional to temperature of the system
III) A change of phase does NOT affect the internal energy of the system because it happens at a constant temperature

I am thinking I and II are true
because
I is basically the definition of internal energy
II - internal energy=kinetic energy + potential energy. Since kinetic energy is proportional to kinetic energy, then internal energy will also be proportional to temperature

I am unsure about these though. Can someone let me know if I am correct or provide me with a correct solution
Thanks
I is true.
II is false.
III is false

I is true by definition.

II is false since internal energy is not proportional to T, in general (it is only the KE part that is proportional to T)

III is false since, at a phase change (e.g. water to steam), we add energy to the system. By conservation of energy, this must manifest itself as an increase in the internal energy. Since we see no rise in T, we can further assert that, at a phase change, there is no increase in the KE of the system, so all of the energy must go to increasing the PE.
3. (Original post by atsruser)
I is true.
II is false.
III is false

I is true by definition.

II is false since internal energy is not proportional to T, in general (it is only the KE part that is proportional to T)

III is false since, at a phase change (e.g. water to steam), we add energy to the system. By conservation of energy, this must manifest itself as an increase in the internal energy. Since we see no rise in T, we can further assert that, at a phase change, there is no increase in the KE of the system, so all of the energy must go to increasing the PE.
Thanks alot!

## Register

Thanks for posting! You just need to create an account in order to submit the post
1. this can't be left blank
2. this can't be left blank
3. this can't be left blank

6 characters or longer with both numbers and letters is safer

4. this can't be left empty
1. Oops, you need to agree to our Ts&Cs to register

Updated: May 27, 2016
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Today on TSR

Find out here

### How to cope with a heavy workload

Poll
Study resources

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.