Sample Test for Unit VII
Potentially useful equations:
Q=mc∆T Q =mL Q =mHcεc= 1 −TC
THε=W
Qin
Specific heat for water = 4186Jkg−1C◦ −1
1. a) Define the kilocalorie.
b) How much heat energy in kilocalories is required to change 2.3 kg of water from 38◦C to
45◦C?
2. a) Define Heat of Combustion.
b) A fuel-oil burning boiler is used to heat water from 20◦C to 60◦C. The Heat of Combustion
for fuel-oil is 4.19 ×107J/kg. The boiler is 40% efficient. How much fuel-oil is required to
heat 5000 kg of water?
3. Fifty grams of glycerine at 35.0◦C is mixed with 1.00 kg of water at 20.0◦C. Find the specific
heat of glycerine if the equilibrium temperature is measured to be 20.42◦C; assume no heat
losses or gains.
4. a) Sketch a typical phase diagram with two phase changes, labeling the axes and transitions.
(Also think about what determines the slopes of the T–Qlines: How are they related to the
specific heat capacity?)
b) Find the total heat energy required to change 2.0 kg of ice at −10◦C into liquid water at
20◦C. (Specific heat for ice = 2100 J kg−1C◦ −1, Latent Heat of Fusion = 3.34 ×105J/kg,
Specific heat for water = 4186Jkg−1C◦ −1, Latent Heat of Vaporization = 22.6×105J/kg).
5. Define and provide an example for each of the three methods of heat transfer.
6. a) State the First Law of Thermodynamics.
b) State the Second Law of Thermodynamics.
7. a) Draw and label a schematic diagram of a heat engine.
b) Determine the Carnot efficiency of a steam turbine engine which operates between a high
temperature of 550◦C and a low temperature of 90◦C.
Short Answers:
1. a) The kcal is the heat energy needed to raise 1 kg of water by 1 C◦(from 14.5◦C to 15.5◦C).
b) Q=mc∆T, where cwater = 1 kcal kg−1C◦−1(= 41861 J kg−1C◦−1), so that
Q= (2.3 kg)(1 kcal kg−1C◦−1)(45◦C−38◦C) = 16.1 kcal.
