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JAMB Physics 2012 Paper

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Question : 19

Total: 42

The quantity of heat energy required to melt completely 1 kg of ice at - 30^oC is

[latent heat of fusion = 3.5 x 10 ⁵Jkg ^-1, specific heat capacity of ice = 2.1x10 ³Jkg ^-1K ^-1]

4.13x10 ⁶J
4.13x10 ⁵J
3.56x10 ⁴J
3.56x10 ²J

Solution:

Concept:

Melting ice at

-30^\circ\mathrm{C}

requires two steps: warming the ice to

0^\circ\mathrm{C}

, then melting it.

Explanation:

Heat needed to warm ice from

-30^\circ\mathrm{C}

to

0^\circ\mathrm{C}

:

Q_1 = mc\Delta\theta = 1 \times 2.1 \times 10^3 \times 30 = 6.3 \times 10^4 \, \mathrm{J}

Heat needed to melt the ice at

0^\circ\mathrm{C}

:

Q_2 = mL = 1 \times 3.5 \times 10^5 = 3.5 \times 10^5 \, \mathrm{J}

Total heat energy:

Q = Q_1 + Q_2 = 6.3 \times 10^4 + 3.5 \times 10^5 = 4.13 \times 10^5 \, \mathrm{J}

Answer:

B.

4.13 \times 10^5 \, \mathrm{J}

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