Heat%20and%20the%20First%20Law%20of%20Thermodynamics

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Chapter 20

• Heat and the First Law of Thermodynamics

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Quick Quiz 20.1
Imagine you have 1 kg each of iron, glass, and
water, and that all three samples are at 10C.
Rank the samples from lowest to highest
temperature after 100 J of energy is added to
each sample. (a) iron, glass, water (b) iron,
water, glass (c) glass, iron, water (d) glass,
water, iron (e) water, glass, iron (f) water,
iron, glass
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Quick Quiz 20.1
Answer (e). Because water has the highest
specific heat (4 186 J/kg C), it has the
smallest change in temperature. Glass is next
(837 J/kg C), and iron is last (448 J/kg C).
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Quick Quiz 20.2
Imagine you have 1 kg each of iron, glass, and
water, and that all three samples are at 10C.
Rank them from least to greatest amount of energy
transferred by heat if each sample increases in
temperature by 20C. (a) iron, glass, water (b)
iron, water, glass (c) glass, iron, water (d)
glass, water, iron (e) water, glass, iron (f)
water, iron, glass
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Quick Quiz 20.2
Answer (a). Iron, glass, water. For a given
temperature increase, the energy transfer by heat
is proportional to the specific heat.
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Quick Quiz 20.3
Suppose energy is added to an ice cube until it
eventually vaporizes into steam, and we graph the
internal energy of the system as a function of
energy input. What would this graph look like?
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Quick Quiz 20.3
Answer The figure below shows a graphical
representation of the internal energy of the ice
in parts A to E as a function of energy added.
Notice that this graph looks quite different from
Figure 20.2 it doesnt have the flat portions
during the phase changes. Regardless of how the
temperature is varying in Figure 20.2, the
internal energy of the system simply increases
linearly with energy input.
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Quick Quiz 20.4
Calculate the slopes for the A, C, and E portions
of the figure below. Rank the slopes from least
to greatest. (a) A, C, E (b) A, E, C (c) C, E,
A (d) C, A, E (e) E, A, C (f) E, C, A
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Quick Quiz 20.4
Answer (d). C, A, E. The slope is the ratio of
the temperature change to the amount of energy
input. Thus, the slope is proportional to the
reciprocal of the specific heat. Water, which has
the highest specific heat, has the smallest slope.
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Quick Quiz 20.5
In the last three columns of the following table,
fill in the boxes with -, , or 0. For each
situation, the system to be considered is
identified.
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Quick Quiz 20.5
Answer
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Quick Quiz 20.6a
Characterize path A in the figure below (a)
isobaric (b) isovolumetric (c) isothermal (d)
adiabatic
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Quick Quiz 20.6a
Answer (b).
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Quick Quiz 20.6b
Characterize path B in the figure below. Note
that Q 0. (a) isobaric (b) isovolumetric (c)
isothermal (d) adiabatic
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Quick Quiz 20.6b
Answer (d).
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Quick Quiz 20.6c
Characterize path C in the figure below (a)
isobaric (b) isovolumetric (c) isothermal (d)
adiabatic
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Quick Quiz 20.6c
Answer (c).
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Quick Quiz 20.6d
Characterize path D in the figure below (a)
isobaric (b) isovolumetric (c) isothermal (d)
adiabatic
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Quick Quiz 20.6d
Answer (a).
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Quick Quiz 20.7
An ice cube wrapped in a wool blanket will remain
frozen for a _____ length of time than an
identical ice cube exposed to air at room
temperature. (a) shorter (b) same (c) longer
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Quick Quiz 20.7
Answer (c). The blanket acts as a thermal
insulator, slowing the transfer of energy by heat
from the air into the cube.
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Quick Quiz 20.8
You have two rods of the same length and diameter
but they are formed from different materials. The
rods will be used to connect two regions of
different temperature such that energy will
transfer through the rods by heat. They can be
connected in series, as in part (a) of the figure
below, or in parallel, as in part (b). In which
case is the rate of energy transfer by heat
larger? (a) when the rods are in series (b) when
the rods are in parallel (c) The rate is the
same in both cases.
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Quick Quiz 20.8
Answer (b). In parallel, the rods present a
larger area through which energy can transfer and
a smaller length.