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

Thermal physics -- Latent heat melting ice

  • Thread starter Cici2017
  • Start date
  • #1
Cici2017

Homework Statement


Question (b) (iii)
屏幕快照 2017-11-07 下午11.25.14.png

Homework Equations




The Attempt at a Solution


The energy required to melt the ice is
Q1=mL=3*0.025*3.3*10^5=24750J
The energy released by water is
Q2=mcT=0.33*4200*(22-T)

Shall I calculate the energy that the ice needs after it melts into water?
i.e. Q3=0.075*4200*(0-T)

So Q1+Q3=Q2 and then just solve for T?

Is that right? I did it this way but got a different answer to the mark scheme.
 

Attachments

Answers and Replies

  • #2
DoItForYourself
Will the final temperature T be greater or lower than 0°C?
 
  • #3
19,799
4,048
Do the calculation assuming that all the ice melts. If the final calculated temperature comes out above 0C, you're through. What if the final calculated temperature comes out below 0C? Then what can you say about the final temperature? How does this change the calculation?
 
  • #4
Cici2017
Will the final temperature T be greater or lower than 0°C?
Should be greater than 0
 
  • #5
Cici2017
Do the calculation assuming that all the ice melts. If the final calculated temperature comes out above 0C, you're through. What if the final calculated temperature comes out below 0C? Then what can you say about the final temperature? How does this change the calculation?
What calculations do I need to do?
 
  • #6
19,799
4,048
What calculations do I need to do?
Your expression for Q3 has the wrong sign.

So, what do you get when you solve your equations for T?
 
  • #7
Cici2017
Your expression for Q3 has the wrong sign.

So, what do you get when you solve your equations for T?
T=4.05
 
  • #8
19,799
4,048
T=4.05
Good. When you substitute this back into your equations, does this satisfy them?
 
  • #9
Cici2017
Good. When you substitute this back into your equations, does this satisfy them?
um... not quite. I got Q1+Q3=26025.75 and Q2=24878.7
 
  • #10
DoItForYourself
Should be greater than 0
Yes, in case the ice melts completely, the temperature should be greater than 0°C. If the ice does not melt compeltely, this means that the thermal energy of the water is not enough and its initial temperature must be increased in order to melt completely the ice.
 
Last edited by a moderator:
  • #11
haruspex
Science Advisor
Homework Helper
Insights Author
Gold Member
32,545
4,979
T=4.05
As you found, this is not right. Please post your working.
 
  • #12
Cici2017
As you found, this is not right. Please post your working.
I followed the logic in my attempt. Is that wrong or is there something wrong in my calculation?
 
  • #13
haruspex
Science Advisor
Homework Helper
Insights Author
Gold Member
32,545
4,979
I followed the logic in my attempt. Is that wrong or is there something wrong in my calculation?
Did you correct the sign error pointed out in post #6?
If so, you should have got the right answer. I cannot tell where you went wrong without seeing your working.
 

Related Threads for: Thermal physics -- Latent heat melting ice

Replies
3
Views
18K
Replies
2
Views
5K
Replies
4
Views
2K
  • Last Post
Replies
6
Views
8K
  • Last Post
Replies
1
Views
2K
  • Last Post
Replies
8
Views
3K
  • Last Post
Replies
2
Views
2K
  • Last Post
Replies
1
Views
5K
Top