Questions: Heat Transfer Calculations: Q = mcΔT

Question 1

How much heat is needed to raise the temperature of 2 kg of water from 20°C to 70°C? (c_water = 4,186 J/kg·°C)

• A. 418,600 J
• B. 8,372 J
• C. 293,020 J
• D. 585,040 J

Answer: (A)

Q = mcΔT = 2 × 4,186 × (70 - 20) = 2 × 4,186 × 50 = 418,600 J.

Question 2

If Q is negative in the equation Q = mcΔT, it means the object is losing heat energy.

• T. True
• F. False

Answer: True

A negative Q indicates the object's temperature decreased (negative ΔT), meaning it released heat energy to its surroundings.

Question 3

0.5 kg of iron (c = 450 J/kg·°C) absorbs 9,000 J of heat. What is its temperature change?

Model answer: 40°C, because ΔT = Q/(mc) = 9,000/(0.5 × 450) = 9,000/225 = 40°C.

Rearranging Q = mcΔT gives ΔT = Q/(mc) = 9,000/(0.5 × 450) = 40°C.