Chapter 4 | 217If the initial temperature of the egg is 5°C, the maximum
amount of heat transfer to the egg is
(a) 12 kJ (d) 18 kJ
(b) 30 kJ (e) infinity
(c) 24 kJ
4 –162 An apple with an average mass of 0.18 kg and aver-
age specific heat of 3.65 kJ/kg · °C is cooled from 22°C to
5°C. The amount of heat transferred from the apple is
(a) 0.85 kJ (d) 11.2 kJ
(b) 62.1 kJ (e) 7.1 kJ
(c) 17.7 kJ
4 –163 The specific heat at constant pressure for an ideal gas
is given by cp0.9 (2.7 10 ^4 )T(kJ/kg · K) where Tis in
kelvin. The change in the enthalpy for this ideal gas under-
going a process in which the temperature changes from 27 to
127°C is most nearly
(a) 90 kJ/kg (d) 108.9 kJ/kg
(b) 92.1 kJ/kg (e) 105.2 kJ/kg
(c) 99.5 kJ/kg
4 –164 The specific heat at constant volume for an ideal gas
is given bycv0.7 (2.7 10 ^4 )T(kJ/kg · K) where Tis
in kelvin. The change in the internal energy for this ideal gas
undergoing a process in which the temperature changes from
27 to 127°C is most nearly
(a) 70 kJ/kg (d) 82.1 kJ/kg
(b) 72.1 kJ/kg (e) 84.0 kJ/kg
(c) 79.5 kJ/kg
4 –165 A piston–cylinder device contains an ideal gas. The
gas undergoes two successive cooling processes by rejecting
heat to the surroundings. First the gas is cooled at constant
pressure until T 2 ^3 – 4 T 1. Then the piston is held stationary
while the gas is further cooled to T 3 ^1 – 2 T 1 , where all temper-
atures are in K.
- The ratio of the final volume to the initial volume of the
gas is
(a) 0.25 (d) 0.75
(b) 0.50 (e) 1.0
(c) 0.67 - The work done on the gas by the piston is
(a) RT 1 /4 (d) (cv cp)T 1 /4
(b) cvT 1 /2 (e) cv (T 1 T 2 )/2
(c) cpT 1 /2 - The total heat transferred from the gas is
(a) RT 1 /4 (d) (cv cp)T 1 /4
(b) cvT 1 /2 (e) cv (T 1 T 3 )/2
(c) cpT 1 /2
4 –166 Saturated steam vapor is contained in a piston–cylin-
der device. While heat is added to the steam, the piston is held
stationary, and the pressure and temperature become 1.2 MPa
and 700°C, respectively. Additional heat is added to the steam
until the temperature rises to 1200°C, and the piston moves to
maintain a constant pressure.- The initial pressure of the steam is most nearly
(a) 250 kPa (d) 1000 kPa
(b) 500 kPa (e) 1250 kPa
(c) 750 kPa - The work done by the steam on the piston is most nearly
(a) 230 kJ/kg (d) 2340 kJ/kg
(b) 1100 kJ/kg (e) 840 kJ/kg
(c) 2140 kJ/kg - The total heat transferred to the steam is most nearly
(a) 230 kJ/kg (d) 2340 kJ/kg
(b) 1100 kJ/kg (e) 840 kJ/kg
(c) 2140 kJ/kg
Design, Essay, and Experiment Problems
4 –167 Using a thermometer, measure the boiling tempera-
ture of water and calculate the corresponding saturation pres-
sure. From this information, estimate the altitude of your
town and compare it with the actual altitude value.
4 –168 Find out how the specific heats of gases, liquids, and
solids are determined in national laboratories. Describe the
experimental apparatus and the procedures used.
4 –169 Design an experiment complete with instrumenta-
tion to determine the specific heats of a gas using a resistance
heater. Discuss how the experiment will be conducted, what
measurements need to be taken, and how the specific heats
will be determined. What are the sources of error in your sys-
tem? How can you minimize the experimental error?
4 –170 Design an experiment complete with instrumenta-
tion to determine the specific heats of a liquid using a resis-
tance heater. Discuss how the experiment will be conducted,
what measurements need to be taken, and how the specific
heats will be determined. What are the sources of error in
your system? How can you minimize the experimental error?
How would you modify this system to determine the specific
heat of a solid?
4 –171 You are asked to design a heating system for a
swimming pool that is 2 m deep, 25 m long, and 25 m wide.
Your client desires that the heating system be large enough to
raise the water temperature from 20 to 30°C in 3 h. The rate
of heat loss from the water to the air at the outdoor design
conditions is determined to be 960 W/m^2 , and the heater must
also be able to maintain the pool at 30°C at those conditions.
Heat losses to the ground are expected to be small and can be
disregarded. The heater considered is a natural gas furnace
whose efficiency is 80 percent. What heater size (in kW
input) would you recommend to your client?
4 –172 It is claimed that fruits and vegetables are cooled by
6°C for each percentage point of weight loss as moisture