Exam 14: Second Law of Thermodynamics

A Carnot air conditioner has a coefficient of performance of 17.0 and removes 72.0 MJ of thermal energy from the interior of a house every hour.How much power does it consume?

Suppose that the Department of Energy develops a new reversible engine that has a coefficient of performance (COP)of 4.0 when operated as a refrigerator and a COP of 5.0 when operated as a thermodynamic pump.What is its thermal efficiency when operated as a thermodynamic engine doing work?

What is the change in entropy when 15.0 g of water at 100°C are turned into steam at 100°C? The latent heat of vaporization of water is 22.6 × 10⁵ J/kg.

A certain automobile engine takes in 4.00 kJ of energy and performs 1.10 kJ of mechanical work in each cycle. (a)Calculate the engine's efficiency. (b)How much thermal energy is "wasted" in each cycle?

An ideal Carnot refrigerator with a performance coefficient (COP)of 5.0 cools items inside of it to $5.0 ^ { \circ } \mathrm { C }$ What is the high temperature needed to operate this refrigerator?

A refrigerator has a performance coefficient (COP)of 1.15,and it extracts 7.95 J of energy from the cold reservoir during each cycle. (a)How much work is done on the gas in each cycle? (b)How much energy is exhausted into the hot reservoir in each cycle?

An ideal reversible thermodynamic pump is taking heat from the outside air at -10.0°C and discharging it into the house at 18.0°C.What is the coefficient of performance of this thermodynamic pump?

A thermodynamic engine receives 7000 J of energy and loses 3000 J in each cycle.What is the efficiency of this engine?

An ideal Carnot refrigerator powered from an electrical outlet takes heat from water at 0.0°C and rejects energy to a room at $20.0 ^ { \circ } \mathrm { C }$ How much electrical energy must be supplied to the refrigerator so it will convert 78 g of water at 0.0°C to ice at 0.0°C.The latent heat of fusion of water is 3.34 × 10⁵ J/kg.

A certain thermodynamic engine extracts 1.30 kJ of thermal energy from a hot temperature reservoir and discharges 0.70 kJ of energy to a cold temperature reservoir.What is the efficiency of this engine?

What is the entropy change of 450 g of water when it changes from (a)liquid to steam at its usual boiling point and (b)ice to liquid at its usual melting point? For water,L_F = 0.334 MJ/kg,L_V = 2.26 MJ/kg.

One of the most efficient engines built so far has the following characteristics: The combustion chamber temperature is 1900°C,the exhaust temperature = 430°C,7.0 × 10⁹ cal of fuel produces 1.4 × 10¹⁰ J of work in one hour.(1 cal = 4.186 J) (a)What is the actual efficiency of this engine? (b)What is the power output of this engine? (c)What would be the maximum possible efficiency for an engine using the same temperature extremes?

An inventor tries to sell you his new thermodynamic engine that takes in 40 J of energy at 87°C on each cycle,expels 30 J at 27°C,and does 10 J of work.Would it be wise to invest in this engine? Back up your conclusion with numerical calculations.

An ideal Carnot thermodynamic engine operates between reservoirs at 1740 K and $150 \mathrm {~K} .$ In each cycle,260 J of thermal energy is rejected to the low temperature reservoir.In each cycle,how much mechanical work W is performed by the engine?

When 1.0 kg of steam at 100°C condenses to water at 100°C,what is the change in entropy of the steam? The latent heat of vaporization of water is 22.6 × 10⁵ J/kg.

During each cycle,the compressor in a certain ideal Carnot refrigerator performs 480 J of work to remove 150 J of thermal energy from the interior of the refrigerator.How much thermal energy do the coils behind the refrigerator discharge into the kitchen each cycle?

During each cycle,a refrigerator removes 20.0 kJ of heat from the freezing compartment and ejects 24.0 kJ into a room. (a)How much work per cycle is required each cycle to run this refrigerator? (b)What is the coefficient of performance of this refrigerator?

A 0.42-kg quantity of ethanol,in the liquid state at its melting point of -114.4°C,is frozen at atmospheric pressure.The heat of fusion of ethanol is 1.04 × 10⁵ J/kg,and its molecular mass is 46.1 g/mol.What is the change in the entropy of the ethanol as it freezes?

What is the efficiency of an ideal Carnot engine operating between a reservoir in which ice and water coexist,and a reservoir in which water and steam coexist? The pressure is constant at 1.0 atm for both reservoirs.

When water at 0°C freezes,the entropy of the water