Heat

Question 1

What is thermal equilibrium?

Answer 1

Two objects are said to be in thermal equilibrium, if there is no net flow of heat between them. They are then at the same temperature.

Question 2

What is absolute scale of temperature? What is absolute zero?

Answer 2

The absolute scale of temperature is a theoretical scale that is independent of the properties of any particular substance.
Absolute zero: Temperature at which all substances have a minimum internal energy
{NOT: zero internal energy}

Question 3

Equation for ideal gas?

Answer 3

pV = n R T
pV = N k T

Question 4

What is an ideal gas?

Answer 4

An ideal gas is one that obeys the equation pV = nRT for all values of pressure, volume and temperature.

Question 5

How molecular movement causes pressure by gas?

Answer 5

x

Question 6

What are the assumptions for kinetic theory of gases?

Answer 6

x

Question 7

How to derive p=Nm/3V?

Answer 7

x

Question 8

What is the formula for average KE of one molecule(not one mole)?

Answer 8

1⁄2 m =3/2kT

Question 9

What is the average KE of one mole?

Answer 9

1⁄2 Mr =3/2RT

Question 10

What is specific heat capacity?

Answer 10

Specific heat capacity (c) is defined as the amount of energy needed to produce unit temperature change for unit mass {NOT: 1 kg} of a substance, without causing a change in state.

Question 11

What is specific latent heat of vaporisation?

Answer 11

is defined as the energy per unit mass required to change a substance from liquid phase to gaseous phase without a change of temperature.

Question 12

What is specific latent heat of fusion?

Answer 12

is defined as the energy per unit mass required to change a substance from solid phase to liquid phase without a change of temperature.

Question 13

What is internal energy?

Answer 13

Internal Energy (U) of a substance is the sum of the kinetic energy of the molecules due to their random motion and the potential energy of the molecules (due to the intermolecular forces).

Question 14

What doesinternal energy is determined by the state of the system mean?

Answer 14

Internal energy is determined by the values of N & T of the current state, i.e. it is independent of the path taken to reach its current state. Thus if a system undergoes a change from one state to another {for eg, from point A on p-V graph to another point B}, its change in internal energy is the same, regardless of which path it has taken to get from A to B.

Question 15

What is the formula of internal energy for ideal gas?

Answer 15

For an ideal gas, internal energy U = Sum of the KE of all the molecules only {since PE = 0, due to zero intermolecular forces}

Question 16

What is the first law of thermodynamics?

Answer 16

The increase in internal energy of a system is equal to the sum of the heat supplied to the system and the work done on the system.

Question 17

What is the formula of work done by gas?

Answer 17

Work done by gas = p ΔV; Work done on gas = - pΔV

Question 18

Why is specific latent heat of vap. higher than that of fusion?

Answer 18

During vaporisation, there is a greater increase in volume than in fusion; thus more work is done against atmospheric pressure during vaporisation.
The greater increase in volume also means the increase in the (molecular) potential energy, & hence, internal energy, during vaporisation > that during melting.