calculating heat required for phase change.

[Smooth Operater]

how much heat must be added to bring 20 g of ice at 0 celcius to water vapor at 100 celcius? (heat of fusion of ice 80 cal/g; the heat of vaporization of water is 540 cal/g)

can anyone show a sample calculation for this question. I just need to check if I am on the right track.

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[dat_student]

how much heat must be added to bring 20 g of ice at 0 celcius to water vapor at 100 celcius? (heat of fusion of ice 80 cal/g; the heat of vaporization of water is 540 cal/g)

can anyone show a sample calculation for this question. I just need to check if I am on the right track.

(20 g * 80 cal/g) + [(100c - 0c) * 20 g * 1 cal/(g*c)] + (540 cal/g * 20)

 

[scuzfly]

what equation is that?
could anyone explain it more? I'm having the same problem and I don't quite understand the process of calculating it.

I figured I would bring up an old thread instead of start a new one...even though its 2 years old.

 

[klutzy1987]

what equation is that?
could anyone explain it more? I'm having the same problem and I don't quite understand the process of calculating it.

I figured I would bring up an old thread instead of start a new one...even though its 2 years old.

The equation is Q=M C deltaT

Where M=mass
C=specific heat
Q= Heat required
That is to change the temperature of the water from 0 to 100 degrees.


To change the ice to liquid or liquid to gas we use the formula Q=(M*specific heat). So you would add the 3 values together, (the value of heat required to change it from 0-100 + the amount of heat required to make ice to water, +the amount of heat required to turn water to gas).

This equels the total heat required.

 

[scuzfly]

The equation is Q=M C deltaT

Where M=mass
C=specific heat
Q= Heat required
That is to change the temperature of the water from 0 to 100 degrees.

To change the ice to liquid or liquid to gas we use the formula Q=(M*specific heat). .

Beacuse there is no change in temp during a phase change correct? so delta T = 0

So you would add the 3 values together, (the value of heat required to change it from 0-100, the amount of heat required to make ice to water, and the amount of heat required to turn water to gas).

This equels the total heat required.

So the heat required to change from 0 to 100 is (80cal/g * 20g * 100C) and it's 100 becuase we go from 0 to 100 so final - initial = 100-0
The heat required to change from solid to liquid is (80 cal/g * 20g) becuase it's a constant temp
lastly toe heat required to turn water to gas would also have a constant temp so it would be (540 cal/g * 20g)

Is that the correct way to calculate it? I had a problem in the blue book that required more steps so I thought I needed to do more.

 

[CannonD]

they meant that from ice-water you use Q=m*Hf, from liquid at 0-100 you use Q=MC(delta T), and finally water at 100 degree-water vapor you would use Q=M(Hv) (heat of vapor) add all those together and you get total energy.

 

[klutzy1987]

Beacuse there is no change in temp during a phase change correct? so delta T = 0




So the heat required to change from 0 to 100 is (80cal/g * 20g * 100C) and it's 100 becuase we go from 0 to 100 so final - initial = 100-0
The heat required to change from solid to liquid is (80 cal/g * 20g) becuase it's a constant temp
lastly toe heat required to turn water to gas would also have a constant temp so it would be (540 cal/g * 20g)

Is that the correct way to calculate it? I had a problem in the blue book that required more steps so I thought I needed to do more.

Yes thats correct and now just add those valued together.