80 g of water at 30 degrees C is poured onto a large block of ice at 0 degrees C. What mass of ice melts? (Specific heat of water = 1 cal/g/°C; latent heat of fusion of ice = 80 cal/g)

30 g
80 g
1600 g
150 g

Correct answer: 30 g

Solution

The water at 30°C cools down to 0°C (the equilibrium temperature with the large ice block) releasing heat Q = 80 g * 1 cal/(g*°C) * 30°C = 2400 cal. This heat melts ice: m_ice = Q / L_f = 2400 / 80 = 30 g.

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