Chapter 12 - THERMODYNAMICS

In a refrigerator one removes heat from a lower temperature
and deposits to the surroundings at a higher temperature. In
this process, mechanical work has to be done, which is provided
by an electric motor. If the motor is of 1kW power, and heat is
transferred from –3°C to 27°C, find the heat taken out of the
refrigerator per second assuming its efficiency is 50% of a
perfect engine.

Consider a cycle tyre being filled with air by a pump. Let V be the
volume of the tyre (fixed) and at each stroke of the pump ΔV(􀀓V)
of air is transferred to the tube adiabatically. What is the work
done when the pressure in the tube is increased from P1 to P2?

A person of mass 60 kg wants to lose 5kg by going up and down
a 10m high stairs. Assume he burns twice as much fat while
going up than coming down. If 1 kg of fat is burnt on expending
7000 kilo calories, how many times must he go up and down to
reduce his weight by 5 kg?

Consider a Carnot’s cycle operating between T1 = 500K and
T2=300K producing 1 k J of mechanical work per cycle. Find the
heat transferred to the engine by the reservoirs.

Air pressure in a car tyre increases during driving. Explain.

Is it possible to increase the temperature of a gas without adding
heat to it? Explain.

If a refrigerator’s door is kept open, will the room become cool or
hot? Explain

Can a system be heated and its temperature remains constant?

Calculate the work done during the isothermal Process?

At 0⁰C and normal atmospheric pressure, the volume of 1g of water increases

from 1cm³ to 1.091 cm3 on free zing. What will be the change in its internal

energy? Normal atmospheric pressure is 1.013x10⁵ N|m² and the latent heat of

melting of ice is 80 cal/g?

State the Second law of thermodynamics and write 2 applications of it?

Why does absolute zero not correspond to zero energy?

A motor car tyre has a Pressure of four atmosphere at a room temperature of

27⁰C. If the tyre suddenly bursts, calculate the temperature of escaping gas?

What is the ratio of slopes of P-V graphs of adiabatic and isothermal process?

What is the ratio of find volume to initial volume if the gas is compressed
adiabatically till its temperature is doubled?

If a air is a cylinder is suddenly compressed by a piston. What happens to the
pressure of air?

A quantity of oxygen is compressed isothermally until its pressure is doubled. It
is then allowed to expand adiabatically until its original volume is restored. Find
the final pressure in terms of initial pressure? Take Y = 1.4?

Five moles of an ideal gas are taken in a Carnot engine working between 100⁰C

and 30⁰C. The useful work done in 1 cycle is 420J. Calculate the ratio of the

volume of the gas at the end and beginning of the isothermal expansion?

A refrigerator placed in a room at 300 K has inside temperature 264K. How
many calories of heat shall be delivered to the room for each 1 K cal of energy
consumed by the refrigerator, ideally?

The internal energy of a compressed gas is less than that of the rarified gas at
the same temperature. Why?

A Carnot engine develops 100 H.P. and operates between 27⁰C and 227⁰C. Find

1) thermal efficiency; 2) heat supplied3) heat rejected?

Differentiate between isothermal and adiabatic process?

State Carnot’s Theorem?

What is the foundation of Thermodynamics?

Derive the equation of state for adiabatic change?

One kilogram molecule of a gas at 400k expands isothermally until its volume is
doubled. Find the amount of work done and heat produced?

Write the sign conventions for the heat and work done during a thermodynamic
process?

Why is conversion of heat into work not possible without a sink at lower
temperature?

A certain gas at atmospheric pressure is compressed adiabatically so that its
volume becomes half of its original volume. Calculate the resulting pressure?

Can a gas be liquefied at any temperature by increase of pressure alone?

State zeroth law of thermodynamics?

Draw a p – v diagram for isothermal and adiabatic expansion?

Briefly describe a Carnot cycle and derive an expression for the efficiency of
Carnot cycle?

Derive an expression for the work done during isothermal expansion?

Calculate difference in efficiency of a Carnot energy working between:-
1) 400K and 350K
2) 350K and 300K

How does second law of thermodynamics explain expansion of gas?

A Carnot engine absorb 6×10⁵ cal at 227⁰c calculate work done per cycle by

the engine if it sink is at 127⁰c?

Does the working of an electric refrigerator defy second law of
thermodynamics?

Can you design heat energy of 100% efficiency?

A refrigerator is to maintain eatables kept inside at 9°C. If room temperature is 36° C, calculate the coefficient of performance.

A thermodynamic system is taken from an original state to an intermediate state by the linear process shown in Fig. (12.13).

An electric heater supplies heat to a system at a rate of 100W. If system performs work at a rate of 75 Joules per second. At what rate is the internal energy increasing?

 A steam engine delivers 5.4×10⁸ J of work per minute and services 3.6 × 10⁹ J of heat per minute from its boiler. What is the efficiency of the engine? How much heat is wasted per minute?

Two cylinders A and B of equal capacity are connected to each other via a stopcock. Acontains a gas at standard temperature and pressure. B is completely evacuated. The entire system is thermally insulated. The stopcock is suddenly opened. Answer the following:
(a) What is the final pressure of the gas in A and B?
(b) What is the change in internal energy of the gas?
(c) What is the change in the temperature of the gas?
(d) Do the intermediate states of the system (before settling to the final equilibrium state) lie on its P-V-T surface?

In changing the state of a gas adiabatically from an equilibrium state A to another equilibrium state B, an amount of work equal to 22.3 J is done on the system. If the gas is taken from state A to B via a process in which the net heat absorbed by the system is 9.35 cal, how much is the net work done by the system in the latter case? (Take 1 cal = 4.19 J)

A cylinder with a movable piston contains 3 moles of hydrogen at standard temperature and pressure. The walls of the cylinder are made of a heat insulator, and the piston is insulated by having a pile of sand on it. By what factor does the pressure of the gas increase if the gas is compressed to half its original volume?

Explain why
(a) Two bodies at different temperatures T₁ and T₂ if brought in thermal contact do not necessarily settle to the mean temperature (T₁ + T₂)/2.
(b) The coolant in a chemical or a nuclear plant (i.e., the liquid used to prevent the different parts of a plant from getting too hot) should have high specific heat.
(c) Air pressure in a car tyre increases during driving.
(d) The climate of a harbour town is more temperate than that of a town in a desert at the same latitude.

What amount of heat must be supplied to 2.0 × 10^–2 kg of nitrogen (at room temperature) to raise its temperature by 45 °C at constant pressure? (Molecular mass of N₂ = 28; R = 8.3 J mol^–1 K^–1.)

 A geyser heats water flowing at the rate of 3.0 litres per minute from 27 °C to 77 °C. If the geyser operates on a gas burner, what is the rate of consumption of the fuel if its heat of combustion is 4.0 × 10⁴ J/g?