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Old Nov 18th 2018, 02:57 PM   #1
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Liquid copper to solid

How much energy must be removed from the system to turn liquid copper of mass 1.5kg at 1083 degrees celsius to solid copper at 1000 degrees celsius?

a. -2.49X10^5J

b. -3.67X10^4J

c. 2.25X10^3J

d. 9.45X10^4J

e. -2.78X10^3J
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Old Nov 18th 2018, 03:52 PM   #2
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"How much energy must be removed ... to turn liquid copper ...to solid copper "

First we need to know is the answer +ve or -ve .... Energy will be removed , you are cooling the copper down so the answer is +ve

So this eliminates answers a b and e ....

latent heat of fusion is the heat removed in turning any liquid into a solid .

You have to use search to find it's value for copper

In addition there is the small amount of heat removed in cooling from 1083 to 1000 . search specific heat of copper.

Give this calculation in your next post and we can move forward .

NONE OF THE CHOICES GIVEN (a b c d or e) ARE CORRECT
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Old Nov 18th 2018, 03:57 PM   #3
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Originally Posted by oz93666 View Post
"How much energy must be removed ... to turn liquid copper ...to solid copper "

First we need to know is the answer +ve or -ve .... Energy will be removed , you are cooling the copper down so the answer is +ve

So this eliminates answers a b and e ....

latent heat of fusion is the heat removed in turning any liquid into a solid .

You have to use search to find it's value for copper

In addition there is the small amount of heat removed in cooling from 1083 to 1000 . search specific heat of copper.

Give this calculation in your next post and we can move forward .

NONE OF THE CHOICES GIVEN (a b c d or e) ARE CORRECT
Ive been trying to solve this for a while now and i havent been getting any of the answers. I tried doing it this way:

Qtot= Mc(Tf-Ti)+ MLf

= (1.5)(387)(1000-1083)+ (1.5)(134x10^4)

Im probably doing this incorrectly anyway. But i just need to find whatever is closest to the answers given.
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Old Nov 18th 2018, 07:25 PM   #4
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well ...from the these figures ...

= (1.5)(387)(1000-1083)+ (1.5)(134x10^4) .... that should be to power 3 not 4

the answer comes out at 249kJ ... which is a ...except they have the sign wrong

The energy which must be removed is 249KJ ...NOT - 249KJ

Also from search I get latent heat as 205 ...a big difference .

I suspect you gave us the question wrongly and 'a' should read 249

Also you have the calculation wrong because of an error in power (3 not 4)

Your problem is not lack of understanding but sloppy work ...Take more care.

Last edited by oz93666; Nov 18th 2018 at 07:31 PM.
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