TBR Q 8.20 - Heat of Phase changes

[Neplina94]

How much energy is required to melt 30 grams of ice at 0°C? (ΔH fusion = 6.0 KL/mole)

It says the math is 1.667 moles * 6.0 KL/mol = 10 KJ

Are the using the usual q=mcΔT to solve this? It doesn't make sense to me? Why don't they incorporate temperature into this equation?


Thanks for helping!!

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[bee17]

while the ice is melting, it does not change temperature. The temperature will remain 0 degrees until all the ice is melted. q=mcΔT is for calculating heat used to change temperature within a single phase. Phase changes are different.

 

[BerkReviewTeach]

How much energy is required to melt 30 grams of ice at 0°C? (ΔH fusion = 6.0 KL/mole)

It says the math is 1.667 moles * 6.0 KL/mol = 10 KJ

Are the using the usual q=mcΔT to solve this? It doesn't make sense to me? Why don't they incorporate temperature into this equation?


Thanks for helping!!

The Q = mc∆T equation is used when the phase remains constant and the temperature changes. For questions of phase change, such as this one, you need to use Q = ∆HFusion x moles (for a solid to liquid or liquid to solid) or Q = ∆HVaporization x moles (for a liquid to gas or gas to liquid).