# Thermal Equilibrium of steam

Hi

Just wondering if I could have a bit of help on this question. Thanks in advance!

3) 100 g of steam at 150_C and 1 kg of water at 20_C are placed together inside
an insulated volume. The specic heat of steam is 2.02x10^3J kg_1K_1, that
of water is 4.19 x10^3 J kg_1K_1 and the latent heat of evaporation of water is
226x10^6 J kg_1.

a) Once the two fluids have come into thermal equilibrium what is left - water or
steam?

b) Calculate the final temperature of the system.

c) Is the net change in the internal energy of the system positive, negative or
zero?

d) Calculate the increase in entropy of the system.

## Answers and Replies

tiny-tim
Science Advisor
Homework Helper
Welcome to PF!

Hi Crocodile! Welcome to PF! Just wondering if I could have a bit of help on this question.

Yes, but only a bit Show us what you've tried, and where you're stuck, and then we'll know how to help! Thanks for the welcome! Well....sorry to sound slightly stupid, but this topic isn't my forte so I haven't really got a clue where to start! Any help at all would be appreciated.

Well, for part b I may have an idea - whether its viable or not I'm not sure... My thoughts are that we know that the total energy of the system must remain constant. Therefore would it be possible to put the specific heat capacity equation of both cases equal to eachother? I.e. the dQ would be the same for both the steam and the water.

Thanks.

tiny-tim
Science Advisor
Homework Helper
Well, for part b … we know that the total energy of the system must remain constant. Therefore would it be possible to put the specific heat capacity equation of both cases equal to eachother? I.e. the dQ would be the same for both the steam and the water.

Essentially, yes …

write out the equation and see what you get. Right, so now I have a ratio of the two dT's - between steam and water. Is that correct? I'm not sure how to use this though... Sorry if this is an elementary question and I'm just being slow!