Exam-style Questions: Temperature and Thermal Properties

  1. It has been suggested that drinking ice-cold water at 0°C can help weight loss because the body uses stored energy in the form of fat to warm the water up to body temperature of 37°C.

    0.5 kg of fat stores about 1.6 x 108 J of energy.

    a) Calculate the mass of ice-cold water that a person would need to drink in order to lose 0.5 kg of fat.

    Specific thermal capacity, c = 4200 J kg-1 K-1

    mass = ............................. kg

    (2 Marks)

    b) Give a reason why it is not sensible to drink ice-cold water in order to lose weight.

    (1 Mark)

    (Marks available: 3)

  2. A can of drinking chocolate contains a chemical heating pack that releases 3.5 x 104 J of energy into drink when activated.

    Calculate the final temperature of the drink assuming no energy is lost to the can or surroundings.

    mass of drink = 0.21 kg

    specific thermal capacity of drink = 4200 J kg-1 K-1

    initial temperature of drink = 20°C

    final temperature of drink = ........................... °C

    (Marks available: 3)

Answer

Answer outline and marking scheme for question:

  1. a) M = Q/C.Δ θ = 1.6 x 108 / a 200 x 37 (1 Mark) = 1030 kg (1 Mark)

    (1000 kg to 2 sf is acceptable)

    (2 Marks)

    b) e.g. lower body temperature, you can't just do it (approx twenty times body mass), too much fluid absorbed.

    (1 Mark)

    (Marks available: 3)

  2. Δ θ = Q/ mc = 3.5 x 104 / 0.21 x 4200 (1 Mark) = 40°C (39.7°C) (1 Mark)

    Final temperature = 40 + 20 = 60°C (1 Mark) (59.7°C)

    (Marks available: 3)