Question

At body temperature, 2404 J is required to evaporate 1 g of water. After vigorous exercise, a person feels chilly because the body is giving up heat to evaporate perspiration. A typical person perspires 25 mL of water after 20 minutes of exercise. How much body heat is used to evaporate this water

Answer 1

Answer: - 1.45 kJ

Step-by-step explanation:

Using q = m x C x (ΔT)

Given : m = 3.8 g , C = 0.900 J/g°C, = -(450-25)°C = -425°C (Since final temperature is less than the initial, the sign is negative)

q = (3.8 g) x (0.900 J/goC) x ( -425 °C)

= -1453.5 J

= -1.45 kJ

Note that negative sign of q indicates that this much heat is released, when the metal cools down.