How much heat energy must be absorbed to completely melt 35.0 grains of H[subscript 2]0(s) at 0 degrees c?

Question

[i got this wrong on a test and i would like to know what the correct answer is and how to get it]

A)9.54J
B)146J
C)11,700J
D)79,100J

this is what i did
q=mC(delta)T
x=35.0(4.18)(273)
but i didnt even get one of the answers. i put A, but that was wrong.
help??

Answer 1

I think you approached the problem incorrectly. There is no temperature change in your problem, so you can't use the formula you mentioned. That formula is used to find the energy change to change the temperature of the water. Instead, you want to use the heat of fusion of water (converting it from solid to liquid at 0C):


Delta H fusion of water is 6.02kJ/mol
MW of water is ~18 g/mol

SO:
q = (Delta)Hfusion x moles
q = Delta H Fusion x (mass / molar mass)
= 6.02 kJ/mol x (35g/18g/mol)
= ~11.7 kJ
= 11, 700 J

Hope that helps you see where you went wrong

BF
4th yr Chem Major
U of O

Answer 2

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