# A Level Physics- latent heat

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#1
Hi TSR, can I have help on this question:

How much heat is needed to convert 80g of ice initially at -10 degrees to 60g of water and 20g of steam at 100 degrees?

I worked out energy for ice to water change and -10 to 0 degree change. I am stuck on what to do next and what value to use for latent heats and heat capacity.

Thanks
0
1 year ago
#2
(Original post by Yodalam)
Hi TSR, can I have help on this question:

How much heat is needed to convert 80g of ice initially at -10 degrees to 60g of water and 20g of steam at 100 degrees?

I worked out energy for ice to water change and -10 to 0 degree change. I am stuck on what to do next and what value to use for latent heats and heat capacity.

Thanks
Qtotal = Q1+Q2+Q3+Q4
Q1 = Heat energy required to convert 80g of ice from -10°c to 0°c.
Q2 = Heat energy required to convert 80g of ice to 80g of water without change in temperature (at 0°c). Use latent heat of fusion.
Q3 = Heat required to convert 80g of water at 0°c to 80g of water at 100°c.
Q4 = Heat required to convert 20g of water to steam without change in temp (the temp remains at 100°c while the change occurs). Use latent heat of vaporisation.

Adding all the four heat energies you will obtain the total heat needed to convert 80g of ice at -10°c to 60g of water at 100°c and 20g of water at 100°c.
1
#3
Qtotal = Q1+Q2+Q3+Q4
Q1 = Heat energy required to convert 80g of ice from -10°c to 0°c.
Q2 = Heat energy required to convert 80g of ice to 80g of water without change in temperature (at 0°c). Use latent heat of fusion.
Q3 = Heat required to convert 80g of water at 0°c to 80g of water at 100°c.
Q4 = Heat required to convert 20g of water to steam without change in temp (the temp remains at 100°c while the change occurs). Use latent heat of vaporisation.

Adding all the four heat energies you will obtain the total heat needed to convert 80g of ice at -10°c to 60g of water at 100°c and 20g of water at 100°c.

Just a question- Why do we need to work -10 to 0 degrees and the energy required to convert from ice to water? Isn't that included in the equation or am I missing something?
0
1 year ago
#4
(Original post by Yodalam)

Just a question- Why do we need to work -10 to 0 degrees and the energy required to convert from ice to water? Isn't that included in the equation or am I missing something?
Because you need to apply heat to change the temperature of ice from -10°c to 0°c.

You apply heat to convert ice to water without change in temperature (it stays at 0°c). When a change of state occurs, heat is applied without change in temp. Ice (at 0°c) changes to water at 0°c and water (at 100°c) changes to steam at 100°c.
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