Question

How much ice must be added to 100g water at 30°C in order to reduce it's temperature to 20°C?
A. 10g
B. 400g
C. 80g
D. None of these

Answer 1

There are two heats involved: the heat to melt the ice and the heat to cool the water.

Heat to melt the ice + Heat to cool the water = 0.

q1+q2 = 0

mΔHfus+mcΔT = 0

m × 333.55 J·g⁻¹ + 254 g × 4.184 J·g⁻¹°C⁻¹ × (-25.0 °C) = 0

333.55 m g⁻¹- 26 600 = 0

m=26600333.55g⁻¹ = 79.7 g=80g
your option is C.80