How is temperature scientifically defined? As the subjective feeling of hot and cold. As the amount of heat an object contains. As the pressure exerted by a fluid. As the average kinetic energy of molecules. What does the zeroth law of thermodynamics state? If two systems are in thermal equilibrium with a third system, they are in thermal equilibrium with each other. The total energy of an isolated system remains constant. Heat flows from hot to cold objects until they reach the same temperature. None

How is temperature scientifically defined? As the subjective feeling of hot and cold. As the amount of heat an object contains. As the pressure exerted by a fluid. As the average kinetic energy of molecules. What does the zeroth law of thermodynamics state? If two systems are in thermal equilibrium with a third system, they are in thermal equilibrium with each other. The total energy of an isolated system remains constant. Heat flows from hot to cold objects until they reach the same temperature. None

Physics for Scientists and Engineers: Foundations and Connections

1st Edition

ISBN:9781133939146

Author:Katz, Debora M.

Publisher:Katz, Debora M.

Chapter21: Heat And The First Law Of Thermodynamics

Section: Chapter Questions

Problem 11PQ

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In a cylinder, a sample of an ideal gas with number of moles n undergoes an adiabatic process. (a) Starting with the expression W=PdV and using the condition PV = constant, show that the work done on the gas is W=(11)(PfVfPiVi) (b) Starting with the first law of thermodynamics, show that the work done on the gas is equal to nCV(Tf Ti). (c) Are these two results consistent with each other? Explain.
This problem compares the energy output and heat transfer to the environment by two different types of nuclear power stationsone with the normal efficiency of 34.0%, and another with an improved efficiency of 40.0%. Suppose both have the same heat transfer into the engine in one day. 2.501014J. (a) How much more electrical energy is produced by the more efficient power station? (b) How much less heat transfer occurs to the environment by the more efficient power station? (One type of more ef?cient nuclear power station, the gas—cooled reactor, has not been reliable enough to be economically feasible in spite of its greater eficiency.)
Give an example of a spontaneous process in which a system becomes less ordered and energy becomes less available to do work. What happens to the system's entropy in this process?
You are working on a summer job at a company that designs non-traditional energy systems. The company is working on a proposed electric power plant that would make use of the temperature gradient in the ocean. The system includes a heat engine that would operate between 20.0C (surface-water temperature) and 5.00C (water temperature at a depth of about 1 km). (a) Your supervisor asks you to determine the maximum efficiency of such a system. (b) In addition, if the electric power output of the plant is 75.0 MW and it operates at the maximum theoretically possible efficiency, you must determine the rate at which energy is taken in from the warm reservoir. (c) From this information, if an electric bill for a typical home shows a use of 950 kWh per month, your supervisor wants to know how many homes can be provided with power from this energy system operating at its maximum efficiency. (d) As energy is drawn from the warm surface water to operate the engine, it is replaced by energy absorbed from sunlight on the surface. If the average intensity absorbed from sunlight is 650 W/m2 for 12 daylight hours on a clear day, you need to find the area of the ocean surface that is necessary for sunlight to replace the energy absorbed into the engine. (e) From this information, you need to determine if there is enough ocean surface on the Earth to use such engines to supply the electrical needs for all the homes associated with the Earths population. Assume the energy use for a home in part (c) is an average over the entire planet. (f) In view of your results in this problem, your supervisor has asked for your conclusion as to whether such a system is worthwhile to pursue. Note that the fuel (sunlight) is free.
(a) How much heat transfer occurs from 20.0 kg of 90.0C water placed in contact with 20.0 kg of 10.0C water, producing a final temperature of 50.0C ? (b) How much work could a Carnot engine do with this heat transfer, assuming it operates between two reservoirs at constant temperatures of 90.0C and 10.0C ? (c) What increase in entropy is produced by mixing 20.0 kg of 90.0C water with 20.0 kg of 10.0C water? (d) Calculate the amount of work made unavailable by this mixing using a low temperature of 10.0C, and compare it with the work done by the Garnet engine. Explicitly show how you follow the steps in the Problem-Solving Strategies for Entropy. (e) Discuss how everyday processes make increasingly more energy unavailable to do work, as implied by this problem.
An electric generating station is designed to have an electric output power of 1.40 MW using a turbine with two-thirds the efficiency of a Carnot engine. The exhaust energy is transferred by heat into a cooling tower at 110C. (a) Find the rate at which the station exhausts energy by heat as a function of the fuel combustion temperature Th. (b) If the firebox is modified to run hotter by using more advanced combustion technology, how does the amount of energy exhaust change? (c) Find the exhaust power for Th = 800C. (d) Find the value of Th for which the exhaust power would be only half as large as in part (c). (e) Find the value of Th for which the exhaust power would be one-fourth as large as in part (c).
Of the following, which is not a statement of the second law of thermodynamics? (a) No heat engine operating in a cycle can absorb energy from a reservoir and use it entirely to do work, (b) No real engine operating between two energy reservoirs can be more efficient than a Carnot engine operating between the same two reservoirs, (c) When a system undergoes a change in state, the change in the internal energy of the system is the sum of the energy transferred to the system by heat and the work done on the system, (d) The entropy of the Universe increases in all natural processes, (e) Energy will not spontaneously transfer by heat from a cold object to a hot object.
A system does 1.80108J of work while 7.50108J of heat transfer occurs to the environment. What is the change in internal energy of the system assuming no other changes (such as in temperature or by the addition of fuel)?
What is the change in entropy in an adiabatic process? Does this imply that adiabatic processes are reversible? Can a process be precisely adiabatic for a macroscopic system?
In a very mild winter climate, a heat pump has heat transfer from an environment at 5.00C to one at 35.0C. What is the best possible coefficient of performance for these temperatures? Explicitly show how you follow the steps in the Problem-Solving Strategies for Thermodynamics.
If a gas is compressed isothermally, which of the following statements is true? (a) Energy is transferred into the gas by heat. (b) No work is done on the gas. (c) The temperature of the gas increases. (d) The internal energy of the gas remains constant. (e) None of those statements is true.
A freezer has a coefficient of performance of 6.30. The freezer is advertised as using 457 kW-h/y. (a) On average, how much energy does the freezer use in a single day? (b) On average, how much thermal energy is removed from the freezer each day? (c) What maximum mass of water at 20.0C could the freezer freeze in a single day? Note: One kilowatt-hour (kW-h) is an amount of energy equal to operating a 1-kW appliance for one hour.