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physics
thermodynamics
Questions and Answers of
Thermodynamics
One of the most efficient heat engines ever built is a steam turbine in the Ohio valley, operating between 430°C and 1 870°C on energy from West Virginia coal to produce electricity for the
A heat engine operating between 200°C and 80.0°C achieves 20.0% of the maximum possible efficiency. What energy input will enable the engine to perform 10.0 kJ of work?
An ideal gas is taken through a Carnot cycle. The isothermal expansion occurs at 250°C, and the isothermal compression takes place at 50.0°C. The gas takes in 1 200 J of energy from the hot
The exhaust temperature of a Carnot heat engine is 300°C. What is the intake temperature if the efficiency of the engine is 30.0%?
A Carnot heat engine uses a steam boiler at 100°C as the high-temperature reservoir. The low-temperature reservoir is the outside environment at 20.0°C. Energy is exhausted to the low-temperature
A power plant operates at a 32.0% efficiency during the summer when the sea water used for cooling is at 20.0°C. The plant uses 350°C steam to drive turbines. If the plant’s efficiency changes in
Argon enters a turbine at a rate of 80.0 kg/min, a temperature of 800°C and a pressure of 1.50 MPa. It expands adiabatically as it pushes on the turbine blades and exits at pressure 300 kPa. (a)
An electric power plant that would make use of the temperature gradient in the ocean has been proposed. The system is to operate between 20.0°C (surface water temperature) and 5.00°C (water
Here is a clever idea. Suppose you build a two-engine device such that the exhaust energy output from one heat engine is the input energy for a second heat engine. We say that the two engines are
A 20.0%-efficient real engine is used to speed up a train from rest to 5.00 m/s. It is known that an ideal (Carnot) engine using the same cold and hot reservoirs would accelerate the same train from
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
At point A in a Carnot cycle, 2.34 mol of a monatomic ideal gas has a pressure of 1 400 kPa, a volume of 10.0 L, and a temperature of 720 K. It expands isothermally to point B, and then expands
What is the coefficient of performance of a refrigerator that operates with Carnot efficiency between temperatures "3.00°C and &27.0°C?
What is the maximum possible coefficient of performance of a heat pump that brings energy from outdoors at "3.00°C into a 22.0°C house? Note that the work done to run the heat pump is also
An ideal refrigerator or ideal heat pump is equivalent to a Carnot engine running in reverse. That is, energy Q c is taken in from a cold reservoir and energy Q h is rejected to a hot reservoir.
A heat pump, shown in Figure P22.26, is essentially an air conditioner installed backward. It extracts energy from colder air outside and deposits it in a warmer room. Suppose that the ratio of the
How much work does an ideal Carnot refrigerator require to remove 1.00 J of energy from helium at 4.00 K and reject this energy to a room-temperature (293-K) environment?
A refrigerator maintains a temperature of 0°C in the cold compartment with a room temperature of 25.0°C. It removes energy from the cold compartment at the rate of 8 000 kJ/h. (a) What minimum
If a 35.0%-efficient Carnot heat engine (Fig. 22.2) is run in reverse so as to form a refrigerator (Fig. 22.5), what would be this refrigerator’s coefficient of performance?
Two Carnot engines have the same efficiency. One engine runs in reverse as a heat pump, and the other runs in reverse as a refrigerator. The coefficient of performance of the heat pump is 1.50 times
In a cylinder of an automobile engine, just after combustion, the gas is confined to a volume of 50.0 cm3 and has an initial pressure of 3.00 X 106 Pa. The piston moves outward to a final volume of
A gasoline engine has a compression ratio of 6.00 and uses a gas for which y = 1.40. (a) What is the efficiency (b) What If? If the actual efficiency is 15.0%, what fraction of the fuel is wasted as
A 1.60-L gasoline engine with a compression ratio of 6.20 has a useful power output of 102 hp. assuming the engine operates in an idealized Otto cycle; find the energy taken in and the energy
The compression ratio of an Otto cycle, as shown in Figure 22.13, is VA/VB = 8.00. At the beginning A of the compression process, 500 cm3 of gas is at 100 kPa and 20.0°C. At the beginning of the
An ice tray contains 500 g of liquid water at 0°C. Calculate the change in entropy of the water as it freezes slowly and completely at 0°C.
At a pressure of 1 atm, liquid helium boils at 4.20 K. The latent heat of vaporization is 20.5 kJ/kg. Determine the entropy change (per kilogram) of the helium resulting from vaporization
Calculate the change in entropy of 250 g of water heated slowly from 20.0°C to 80.0°C. (Suggestion: Note that dQ = mc dT)
In making raspberry jelly, 900 g of raspberry juice is combined with 930 g of sugar. The mixture starts at room temperature, 23.0°C, and is slowly heated on a stove until it reaches 220°F. It is
What change in entropy occurs when a 27.9-g ice cube at -12°C is transformed into steam at 115°C?
The temperature at the surface of the Sun is approximately 5 700 K, and the temperature at the surface of the Earth is approximately 290 K. What entropy change occurs when 1 000 J of energy is
A 1 500-kg car is moving at 20.0 m/s. The driver brakes to a stop. The brakes cool off to the temperature of the surrounding air, which is nearly constant at 20.0°C. What is the total entropy change?
A 1.00-kg iron horseshoe is taken from a forge at 900°C and dropped into 4.00 kg of water at 10.0°C. Assuming that no energy is lost by heat to the surroundings, determine the total entropy change
How fast are you personally making the entropy of the Universe increase right now? Compute an order-of-magnitude estimate, stating what quantities you take as data and the values you measure or
A rigid tank of small mass contains 40.0 g of argon, initially at 200°C and 100 kPa. The tank is placed into a reservoir at 0°C and allowed to cool to thermal equilibrium. (a) Calculate the volume
A 1.00-mol sample of H2 gas is contained in the left-hand side of the container shown in Figure P22.45, which has equal volumes left and right. The right-hand side is evacuated. When the valve is
A 2.00-L container has a center partition that divides it into two equal parts, as shown in Figure P22.46. The left side contains H2 gas, and the right side contains O2 gas. Both gases are at room
A 1.00-mol sample of an ideal monatomic gas, initially at a pressure of 1.00 atm and a volume of 0.025 0 m3, is heated to a final state with a pressure of 2.00 atm and a volume of 0.040 0 m3.
A 1.00-mol sample of a diatomic ideal gas, initially having pressure P and volume V, expands so as to have pressure 2P and volume 2V. Determine the entropy change of the gas in the process.
If you toss two dice, what is the total number of ways in which you can obtain (a) a 12 and (b) a 7?
Prepare a table like Table 22.1 for the following occurrence. You toss four coins into the air simultaneously and then record the results of your tosses in terms of the numbers of heads and tails
Repeat the procedure used to construct Table 22.1 (a) For the case in which you draw three marbles from your bag rather than four and (b) For the case in which you draw five rather than four.
Every second at Niagara Falls (Fig P22.52), some 5 000 m3 of water falls a distance of 50.0 m. What is the increase in entropy per second due to the falling water? Assume that the mass of the
A house loses energy through the exterior walls and roof at a rate of 5 000 J/s = 5.00 kW when the interior temperature is 22.0°C and the outside temperature is "5.00°C. Calculate the electric
How much work is required, using an ideal Carnot refrigerator, to change 0.500 kg of tap water at 10.0°C into ice at - 20.0°C? Assume the temperature of the freezer compartment is held at -20.0°C
A heat engine operates between two reservoirs at T2 = 600 K and T1 = 350 K. It takes in 1 000 J of energy from the higher-temperature reservoir and performs 250 J of work. Find (a) The entropy
Two identically constructed objects, surrounded by thermal insulation, are used as energy reservoirs for a Carnot engine. The finite reservoirs both have mass m and specific heat c. They start out at
In 1816 Robert Stirling, a Scottish clergyman, patented the Stirling engine, which has found a wide variety of applications ever since. Fuel is burned externally to warm one of the engine’s two
An electric power plant has an overall efficiency of 15.0%. The plant is to deliver 150 MW of power to a city, and its turbines use coal as the fuel. The burning coal produces steam that drives the
A power plant, having a Carnot efficiency, produces 1 000 MW of electrical power from turbines that take in steam at 500 K and reject water at 300 K into a flowing river. The water downstream is 6.00
A power plant, having a Carnot efficiency, produces electric power from turbines that take in energy from steam at temperature Th and discharge energy at temperature Tc through a heat exchanger into
An athlete whose mass is 70.0 kg drinks 16 oz (453.6 g) of refrigerated water. The water is at a temperature of 35.0°F. (a) Ignoring the temperature change of the body that results from the water
A 1.00-mol sample of an ideal monatomic gas is taken through the cycle shown in Figure P22.62. The process A → B is a reversible isothermal expansion. Calculate (a) the net work done by the
A biology laboratory is maintained at a constant temperature of 7.00°C by an air conditioner, which is vented to the air outside. On a typical hot summer day the outside temperature is 27.0°C and
A 1.00-mol sample of an ideal gas expands isothermally, doubling in volume. (a) Show that the work it does in ex- panding is W = RT ln 2. (b) Because the internal energy Eint of an ideal gas
A 1.00-mol sample of a monatomic ideal gas is taken through the cycle shown in Figure P22.65. At point A, the pressure, volume, and temperature are Pi , Vi , and Ti , respectively. In terms of R and
A sample consisting of n mol of an ideal gas undergoes a reversible isobaric expansion from volume Vi to volume 3Vi. Find the change in entropy of the gas by calculating
A system consisting of n mol of an ideal gas undergoes two reversible processes. It starts with pressure Pi and volume Vi, expands isothermally, and then contracts adiabatically to reach a final
Suppose you are working in a patent office, and an inventor comes to you with the claim that her heat engine, which employs water as a working substance, has a thermodynamic efficiency of 0.61. She
An idealized diesel engine operates in a cycle known as the air-standard diesel cycle, shown in Figure 22.14. Fuel is sprayed into the cylinder at the point of maximum compression; B. Combustion
A 1.00-mol sample of an ideal gas (y = 1.40) is carried through the Carnot cycle described in Figure 22.11. At point A, the pressure is 25.0 atm and the temperature is 600 K. At point C, the pressure
Suppose 1.00 kg of water at 10.0°C is mixed with 1.00 kg of water at 30.0°C at constant pressure. When the mixture has reached equilibrium, (a) What is the final temperature? (b) Take cP = 4.19
What are some factors that affect the efficiency of automobile engines?
In practical heat engines, which are we better able to control: the temperature of the hot reservoir or the temperature of the cold reservoir? Explain.
A steam-driven turbine is one major component of an electric power plant. Why is it advantageous to have the temperature of the steam as high as possible?
Is it possible to construct a heat engine that creates no thermal pollution? What does this tell us about environmental considerations for an industrialized society?
Does the second law of thermodynamics contradict or correct the first law? Argue for your answer.
“The first law of thermodynamics says you can’t really win, and the second law says you can’t even break even.” Explain how this statement applies to a particular device or process;
In solar ponds constructed in Israel, the Sun’s energy is concentrated near the bottom of a salty pond. With the proper layering of salt in the water, convection is prevented, and temperatures of
Can a heat pump have a coefficient of performance less than unity? Explain.
Give various examples of irreversible processes that occur in nature. Give an example of a process in nature that is nearly reversible.
A heat pump is to be installed in a region where the average outdoor temperature in the winter months is - 20°C. In view of this, why would it be advisable to place the outdoor compressor unit deep
The device shown in Figure Q22.11, called a thermoelectric converter, uses a series of semiconductor cells to convert internal energy to electric potential energy, which we will study in Chapter 25.
Discuss three common examples of natural processes that involve an increase in entropy. Be sure to account for all parts of each system under consideration.
Discuss the change in entropy of a gas that expands (a) at constant temperature and (b) adiabatically.
A thermodynamic process occurs in which the entropy of a system changes by - 8.0 J/K. According to the second law of thermodynamics, what can you conclude about the entropy change of the environment?
If a supersaturated sugar solution is allowed to evaporate slowly, sugar crystals form in the container. Hence, sugar molecules go from a disordered form (in solution) to a highly ordered crystalline
How could you increase the entropy of 1 mol of a metal that is at room temperature? How could you decrease its entropy?
Suppose your roommate is “Mr. Clean” and tidies up your messy room after a big party. Because your roommate is creating more order, does this represent a violation of the second law of
Discuss the entropy changes that occur when you (a) Bake a loaf of bread and (b) Consume the bread.
“Energy is the mistress of the Universe and entropy is her shadow.” Writing for an audience of general readers, argue for this statement with examples. Alternatively, argue for the view that
A classmate tells you that it is just as likely for all the air molecules in the room you are both in to be concentrated in one corner (with the rest of the room being a vacuum) as it is for the air
If you shake a jar full of jellybeans of different sizes, the larger beans tend to appear near the top, and the smaller ones tend to fall to the bottom. Why? Does this process violate the second law
Use nodal analysis to find Io and I1 in the circuit shown below.Figure
A 20.0-L tank contains 0.225 kg of helium at I8.0°C. The molar mass of helium is 4.00 g/mol (a) How many moles of helium are in the tank? (b) What is the pressure in the tank, in Pascal and in
Helium gas with a volume of 2.60 L, under a pressure of 1.30 atm and at a temperature of 41.0oC, is warmed until both pressure and volume are doubled. (a) What is the final temperature? (b) How many
A cylindrical tank has a tight-fitting piston that allows the volume of the tank to be changed. The tank originally contains 0.110 m3 of air at a pressure of 3.40 atm. The piston is slowly pulled out
A 3.00-L tank contains air at 3.00 atm and 20.0oC. The tank is sealed and cooled until the pressure is 1.00 atm. (a) What is the temperature then in degrees Celsius? Assume that the volume of the
(a) Use the ideal-gas law to estimate the number of air molecules in your physics lab room, assuming all the air is N2.(b) Calculate the particle density in the lab (that is, the number of molecules
You have several identical balloons. You experimentally determine that a balloon will break if its volume exceeds 0.900 L. The pressure of the gas inside the balloon equals air pressure (1.00 atm.
A Jaguar XK8 convertible has an eight-cylinder engine. At the beginning of its compression stroke, one of the cylinders contains 499 cm3 of air at atmospheric pressure (1.01 X 105 Pa) and a
A welder using a tank of volume 0.0750 m' fills it with oxygen (molar mass 32.0 g/mol) at a gauge pressure of 3.00 X 105 Pa and temperature of 37.0°C. The tank has a small leak, and in time some of
A large cylindrical tank contains 0.750 m3 of nitrogen gas at 27°C and 1.50 X 105 Pa (absolute pressure). The tank has a tight fitting piston that allows the volume to be changed. What will be the
An empty cylindrical canister 1.50 m long and 90.0 cm in diameter is to be filled with pure oxygen at 22.0°C to store in a space station. To hold as much gas as possible, the absolute pressure of
The gas inside a balloon will always have a pressure nearly equal to atmospheric pressure, since that is the pressure applied to the outside of the balloon. You fill a balloon with helium (a nearly
Deviations from the Ideal-Gas Equation For carbon dioxide gas (CO2), the constants in the van der Waals equation are a = 0.364 j· m3/mol2 and b = 4.27 X 10-5 m3/mol (a) If 1.00 mol of CO2 gas at 350
The total lung volume for a typical physics student is 6.00 L. A physics student fills her lungs with air at an absolute pressure of 1.00 atm. Then, holding her breath, she compresses her chest
A diver observes a bubble of air rising from the bottom of a lake (where the absolute pressure is 3.50 atm) to the surface (where the pressure is 1.00 atm). The temperature at the bottom is 4.0oC,
A metal tank with volume 3.10 L will burst if the absolute pressure of the gas it contains exceeds 100 atm. (a) If 11.0 mol of an ideal gas is put into the tank at a temperature of 23.0oC, to what
Three moles of an ideal gas are in a rigid cubical box with sides of length 0.200 m. (a) What is the force that the gas exerts on each of the six sides of the box when the gas temperature is 20.0oC?
With the assumptions of Example 18.4 (Section 18.1), at what altitude above sea level is air pressure 90% of the pressure at sea level?
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