Exam-style Questions: Temperature and Thermal Properties
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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)
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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 outline and marking scheme for question:
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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)
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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)