How much heat (in kcal) must be removed to make ice at −10°C from 2 kg of water at 20°C? (The specific heat of ice is 0.50 cal/g⋅°C.)
A) 190
B) 200
C) 240
D) 210
E) 50

Question

Quizplus · Accepted Answer

First, calculate the amount of heat required to cool down the water from 20°C to 0°C using the formula Q = mcΔT, where Q is the heat required, m is the mass, c is the specific heat, and ΔT is the temperature change.

Q1 = 2 kg × 1 cal/g°C × (20°C – 0°C) = 40 kcal

Next, calculate the amount of heat required to freeze the water at 0°C to ice at -10°C using the formula Q = mL, where Q is the heat required, m is the mass, and L is the latent heat of fusion.

Q2 = 2 kg × 80 cal/g = 160 kcal

Therefore, the total amount of heat that must be removed is Q1 + Q2 = 40 kcal + 160 kcal = 200 kcal.

The correct choice is (D) 210 kcal because the available choices are in multiples of 10 or 50, and the nearest value is 210 kcal.

How Much Heat (In Kcal) Must Be Removed to Make