Page 29 - FINAL DBS10012_HEAT TEMPERATURE 20102022 (2) (1)

2. How much heat energy is required to change 2 kg of ice at 0°C into water at 20°C?

[Specific latent heat of fusion of water = 334 000 J/kg; specific heat capacity of water =
4200J/ (kg K).]

Solution:

m = 2kg
Specific latent heat of fusion of water, L = 334 000 J/kg

specific heat capacity of water = 4200 J/ (kg K)

3. Starting at 20°C, how much heat is required to heat 0.3 kg of aluminum to its melting point and
then to convert it all to liquid? [Specific heat capacity of aluminium = 900J kg-1 °C-1; Specific

latent heat of aluminium = 321,000 Jkg-1, Melting point of aluminium = 660°C]

Solution:
T, C
o
Energy needed to melt 2kg of ice, Q = mL
660 C
o
Q1 = mL = (2) (334000) = 668000J

o Q = mcθ
20 C
Energy needed to change the temperature from 0°C to 20°C.

Q2 = mcθ = (2) (4200) (20 - 0) = 168000J Heat energy supplied
Total energy needed = Q1 + Q2 = 668000 + 168000 = 836000J
m = 0.3kg

L aluminium = 321 000 J/kg
c aluminium = 900 J/ (kg K)

Energy needed to increase the temperature from 20°C to 660°C

Q1 = mcθ = (0.3) (900) (660 - 20) = 172,800J
Energy needed to melt 0.3kg of aluminium,

Q2 = mL = (0.3) (321000) = 96,300J

Total energy needed = Q1 + Q2 = 172,800 + 96,300 = 269,100J

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