First Law of Thermodynamics

IMPORTANT

First Law of Thermodynamics: Overview

This topic covers concepts, such as, Mathematical Expression for Irreversible Work, Mathematical Expression for Reversible Work, Calculation of Work for Reversible Isobaric Process & Calculation of Work for Irreversible Isochoric Process etc.

Important Questions on First Law of Thermodynamics

EASY
IMPORTANT

1 kg of water at 100°C is converted into steam at 100°C by boiling at atmospheric pressure. The volume of water changes from 1.00×10-3 m3 as a liquid to 1.671 m3 as steam. The change in internal energy of the system during the process will be (Given latent heat of vaporisation =2257 kJ/kg, Atmospheric pressure =1×105 Pa

EASY
IMPORTANT

Given below are two statements:

Statement I: If heat is added to a system, its temperature must increase.

Statement II: If positive work is done by a system in a thermodynamic process, its volume must increase.

In the light of the above statements, choose the correct answer from the options given below

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IMPORTANT

A source supplies heat to a system at the rate of 1000 W. If the system performs work at a rate of 200 W. The rate at which internal energy of the system increases is

MEDIUM
IMPORTANT

The amount of heat supplied to a gas in a system is equal to 1000 J, the system in return does 200 J of work on the surrounding. Find change in internal energy of the gas.

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IMPORTANT

If amount of heat given to the system be 80 Joules and the amount of work done by the system is -20 J . If initial internal energy of the system is 250 J. Final internal energy of the system is

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IMPORTANT

In the case of diatomic gas, the heat given at constant pressure is that part of energy which is used for the expansion of gas, is

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ideal gas expands from volume V1to V2,. This may be achieved by either of the three processes: isobaric, isothermal and adiabatic. Let U be the change in internal energy of the gas, Q be the quantity of heat added to the system and W be the work done by the gas. Identify which of the following statements is false for U?
 

HARD
IMPORTANT

1 g of water at atmospheric pressure has volume of 1 cm3 and when boiled it becomes 1681 cm3 of steam. The heat of vaporization of water is 540 cal g-1. Then the change in its internal energy in this process is 

EASY
IMPORTANT

In an insulated container of water is stirred with a rod to increase the temperature. Which of the following is true?

MEDIUM
IMPORTANT

1 kg of water is heated from 40 °C to 70 °C, if its volume remains constant, then the change in internal energy is (specific heat of water =4148 J kg-1 K-1)

MEDIUM
IMPORTANT

Dry air at 15 °C and 10 atm is suddenly released at atmospheric pressure. Find the final temperature of the air CpCv=1.41.

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IMPORTANT

An ideal gas undergoes a process in which its pressure and volume are related as PVn= constant, where n is a constant. The molar heat capacity for the gas in this process will be zero if

HARD
IMPORTANT

0.5 kg of air at 180°C expands adiabatically to 3 times its original volume. During the expansion, the temperature is decreased to 20°C. Work done during the expansion is 53 kN m. Find Cp,Cv and R.

HARD
IMPORTANT

A monatomic gas expands following a thermodynamic law P=C1V+C2,Where C1,C2 are constants, from state AV0,3P0 to B3V0,P0. What will be the volume of the gas upto which it absorbs heat?

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State first law of thermodynamics.

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In the diagram shown Qiaf =80cal and Wef=50 cal. If W=-30 cal for the curved path f value of Q for path fi, will be

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IMPORTANT

A cylindrical pipe is fitted with a movable adiabatic piston at the centre. We enclose a monoatomic gas on its left-hand side and diatomic gas on right-hand side as shown. The pipe & piston on left-hand side are perfectly insulated from the surroundings. The pipe and piston on right side are perfectly conducting. Both the pistons are pulled out slowly. If the right hand side column expands by 2 cm, what is the expansion in left-hand side?

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EASY
IMPORTANT

Which of the following is the correct equation?

HARD
IMPORTANT

A cube of side 5 cm made of iron and having a mass of 1500 g is heated from 25°C to 400°C. The specific heat for iron is 0.12 cal g-1 °C-1 and the coefficient of volume expansion is 3.5×10-5 C-1, the change in the internal energy of the cube is (atm pressure =1×105 N m-2)

EASY
IMPORTANT

Equal amount of same gas in two similar cylinders A and B, compressed to same final volume from same initial volume one adiabatically and another isothermally, respectively then