10 Temperature and Heat
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Temperature and its Measurement
Heat and Specific Heat Capacity
Joule’s Experiment and the First Law of Thermodynamics
Gas Behavior and the First Law
The Flow of Heat
Answers to Questions
Q1
Q2
Q3
Q4
Q5
Q6
Q7
Q8
Q9
Q10
Q11
Q12
Q13
Q14
Q15
Q16
Q17
Q18
Q19
Q20
Q21
Q22
Q23
Q24
Q25
Q26
An object at 0oC is hotter than an object at 0oF since 0oC is equivalent to 32oF.
A 10 degree change in Celsius is a greater change in absolute temperature than a 10 degree change in
Fahrenheit temperature. Celsius degrees are larger than Fahrenheit degrees.
Yes. The change in volume will indicate a change in temperature, according to the “predictable way”.
No. This is not reliable since it is really a comparison between our skin temperature and the skin
temperature of the other person. We are assuming that our skin temperature is that of a person with normal
body temperature but this may not be the case.
Yes. Zero on the Celsius scale is an arbitrary choice, unlike the zero on the Kelvin scale. People living in the
frost belt experience many winter days with the temperature below the freezing point of water.
No. The zero point on the Kelvin scale represents the lowest possible temperature, and that temperature can
only be attained in an asymptotic limit.
They represent the same temperature as measured on different scales; Celsius vs. Kelvin scales.
Heat will be transferred from the hotter to the colder body until they come to thermal equilibrium. The
temperature of the hotter body will decrease and that of the colder body will increase until they are at the
same temperature.
No. The hotter body cools and the colder body warms so that the final temperature will be intermediate
between the two initial temperatures. They are isolated from any other influence.
No. Different materials have different specific heat capacities. The body with the lower specific heat will have
the higher final temperature.
The city near the desert should cool down more rapidly after sunset. Sand has a lower specific heat
capacity than water.
Yes, if the substance is undergoing a change in phase.
The temperature of the water at the boiling point will remain constant until the water is all converted to steam.
The temperature of the water remains constant as the water freezes. The heat extracted is from the greater
internal energy of the liquid state.
The stirring involves work done on the water which according to the first law of thermodynamics increases the
internal energy by the same amount as an equivalent amount of energy transferred as heat.
Yes. Its temperature will increase because of the pounding. Energy is transferred to the molecules of the
metal, and insulation from its surroundings will have no way of dissipating the heat that is the form of this
transferred energy.
1 cal represents the greater amount of energy.
4.19 J is the equivalent of 1 cal.
No. According to the first law, the internal energy will change equally whether a given amount of energy is
added by performing work on the system or by heat added.
Yes. Internal energy of a system is composed of both kinetic and potential energies of the molecules and
atoms (or more generally, the particles) that make up the system.
The kinetic energy of the falling water adds thermal energy to the pool of water below.
By the First Law of Thermodynamics there is only work done on the system in this adiabatic process. There
will be an increase in the gas’s internal energy that will appear as a rise in temperature.
Yes. Allow the gas to expand in an adiabatic process. Pressure decrease and volume increase provide the
work of the system.
The temperature can remain constant if the work performed by the expanding gas is equal to the heat
added, resulting in a constant internal energy of the gas.
No. In a constant volume process all of the heat added to the gas will show up as an increase in internal
energy, so the temperature will rise.
No, the balloon will not fall. On the contrary, the balloon will rise in response to the decreased density.
The internal energy of the water at 0oC is greater than that of the same amount of ice at 0oC. According to
the first law, the change in internal energy is equal to the difference between the heat added and worked
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Q27
Q28
Q29
Q30
Q31
Q32
Q33
Q34
performed. Here heat is added. Since the system contracts, the surroundings (the atmosphere) do work
on the system, so the work done by the system is negative. Both terms contribute to increase the internal
energy, but the work term is smaller.
No. The metal is a better conductor of heat than the wood so it conducts heat away from the hand.
Convection is the process here involving actual motion of the air through the cracks.
Yes. The temperature of the pavement may be at or below 0oC. At night in cold weather the road surface
may lose energy by radiation and drop below the ambient temperature of the air. Air is not a good thermal
conductor so layers of air near the road surface limit thermal conduction from above which would warm the
road.
Conduction. Glass is a moderately good thermal conductor. We use glass vessels in the chemistry laboratory
and glass in some coffeemakers.
Heat transfer by radiation will occur through a vacuum. That is how we get heat from the sun.
Like carbon dioxide gas, glass is transparent to light in the visible range but opaque to the longer
wavelengths of the infrared. Visible light from the sun can pass through the glass, and be absorbed by
material inside which is reradiated at a longer wavelength which remains trapped in the greenhouse.
The energy received by the solar collector is transferred for use or storage by convection. For the flat plate
collector described in the text, the conducting medium is water that is moved via a pump.
A solar power plant produces electricity without combustion of fossil fuels. Without the process of
combustion, no carbon dioxide will be released and thus will not increase the greenhouse effect of the
atmosphere.
Answers to Exercises
E1
E2
E3
E4
113 F
- 10 C
297 K
a. 35 C
b. 308 K
E5
a.
45.2 C
b. 113.4 F
E6
4200 cal
E7
2232 cal
E8
4.8 kcal
E9
22 C
E10
a. 4800 cal
b. 6.48 x 104 cal
E11
838 J
E12
a. 143.2 cal
b. 48.6 C
E13
500 J
E14
1600 J
W = P∆V=1000 Pa (2.4 m3 - 0.8 m3 ) = 1600 Nm = 1600 J
E15
2100K
Since pressure is constant from the ideal gas law, P/Nk = T/V = constant.
if
E16
E17
E18
T 
T
T
T
 700K 
 constant then 2  1  T2  V2  1   2.4m3 
  2100K
V
V2 V1
 0.8m3 
 V1 
700 J; Flow out of system.
1595 J
a. 600 J
b. 1.43 C
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Answers to Synthesis Problems
SP1
a. 90 F
b. 50 K
c. No. The temperature degree intervals are the
same.
SP2
a. 30 C
b. 86 F
c. 303 K
d. Larger. Each student degree equals almost two degrees Celsius.
SP3
a. 13,500 cal
b. 3750 cal
c. 17,250 cal
d. No. Heat is needed to raise ice to 0 C with different specific heat capacity than water. different specific
heat capacity than water.
SP4
a. 1500 cal
b. 0.117 cal/g Co
c. 850 g
SP5
a. 2038 J
b. 486 cal
c. 1.2 C
d. Yes. The calorie and the Joule units are not equal.
SP6
a. 0.45 m3
PV  NkT 
V2 
V
V
V Nk

 constant  2  1 
T
P
T2 T1
V1
0.15m3
 T2 
 750K  0.45m3
T1
250K
b. ∆V = V2 – V1 = 0.45 – 0.15 = 0.30m3
c.
W = P∆V = 1800 Pa (0.30m 3) = 540J
d. The work will not be the same. V2 
V1
0.24m3
 T2 
 750K  0.72m3
T1
250K
∆V = V2 – V1 = 0.72 – 0.24 = 0.48m3
W = P∆V = 1800 Pa (0.48m 3) = 864J
e. No the amount of gas is not the same in both situations. Since PV = NkT, and for both situations the P
and T are the same, if V changes, N must also change.
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