PHYS 101 Chapter Notes - Chapter 15: Isothermal Process, Thermodynamics, Thermal Pollution

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The first law of thermodynamics states that the change in internal energy (cid:1847) of a system is equal to the heat added to the system, (cid:1843), minus the work done by the system, (cid:1849): This is a statement of the conservation of energy, and is found to hold for all types of processes. An isothermal process is a process carried out at constant temperature. In an adiabatic process, no heat is exchange ((cid:1843)=(cid:882)). The work (cid:1849) is done by a gas at constant pressure (cid:1842) is given by: (cid:1849)=(cid:1842) (cid:1848) Where (cid:1848) is the change in volume of the gas. A heat engine is a device for changing thermal energy, by means of heat flow between two temperatures, into useful work. exhausted at low temperature to the environment, hence: The efficiency of a heat engine is defined as the ratio of the work (cid:1849) done by the engine to the heat input (cid:1843).

Related Questions

Part A Which physical law underlies the first law of thermodynamics?

conservation of matter

increase in entropy

conservation of energy

conservation of work

Part B The quantity Q is the __________ that is added to the system.

heat

work

entropy

internal energy

Part C The quantity W in the first law refers to the __________.

work done on the system

work done by the system

change of energy in the system

change of volume in the system

Part D The quantity ΔU in the first law of thermodynamics is the change in the __________ of the system.

Choose the correct option.

entropy

internal energy

heat energy

temperature

azurefish181

A heat engine consists of two isothermal paths (ab withT_H = 1000 K and cd with T_L = 300 K)and two isochoric paths (bc and da). Assume thatthe working substance is 2 moles of an ideal monatomic gas. Thework done by an ideal gas along sothermal paths can be calculatedusing the formula W = nRT ln(V_final/V_initial) where T is the constanttemperature along the isotherm and V_final(V_initial) is the volume of the gas in the final(initial) state. Using the first law of thermodynamics, Eq. (??),and the formula for heat during constant volume processes, (Q =nC_v ÎT) determine the following:

W_ab Q_ab

W_bc Q_bc

W_cd W_cd

W_da Q_da

A firebox is at 750 K, and the ambient temperature is
300 K. The efficiency of a Carnot engine doing 150 J of work
as it transports energy between these constant- temperature
baths is 60.0%. The Carnot engine must take in energy
150 J/0.600 5 250 J from the hot reservoir and must put
out 100 J of energy by heat into the environment. To follow
Carnotâs reasoning, suppose some other heat engine
S could have an efficiency of 70.0%. (a) Find the energy
input and exhaust energy output of engine S as it does 150 J
of work. (b) Let engine S operate as in part (a) and run the
Carnot engine in reverse between the same reservoirs. The
output work of engine S is the input work for the Carnot
refrigerator. Find the total energy transferred to or from
the firebox and the total energy transferred to or from the
environment as both engines operate together. (c) Explain
how the results of parts (a) and (b) show that the Clausius
statement of the second law of thermodynamics is violated.
(d) Find the energy input and work output of engine S as it
puts out exhaust energy of 100 J. Let engine S operate as in
part (c) and contribute 150 J of its work output to running theCarnot engine in reverse. Find (e) the total energy the
firebox puts out as both engines operate together, (f) the
total work output, and (g) the total energy transferred to
the environment. (h) Explain how the results show that
the KelvinâPlanck statement of the second law is violated.
Therefore, our assumption about the efficiency of engine S
must be false. (i) Let the engines operate together through
one cycle as in part (d). Find the change in entropy of the
Universe. (j) Explain how the result of part (i) shows that
the entropy statement of the second law is violated.

PHYS 101 Chapter Notes - Chapter 15: Isothermal Process, Thermodynamics, Thermal Pollution

PHYS 101 Full Course Notes

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