latent heat, energy absorbed or released by a substance during a change in its physical state (phase) that occurs without changing its temperature.The latent heat is normally expressed as the amount of heat (in units of joules or calories) per mole or unit mass of the substance undergoing a change of state.The latent heat of condensation is defined as the heat released when one mole of the substance condenses. The temperature does not change during this process, so heat released goes directly into changing the state of the substance.Latent heat is the heat energy required to change a substance from one state to another.Energy is required to change from solid to liquid, liquid to gas (evaporation), or solid to gas (sublimation). Energy will be released to change from liquid to solid (fusion), gas to liquid (condensation), or gas to solid.

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What is latent heat?

Important Questions on Thermal Properties of Matter

EASY

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Change of State

In an experiment, a sphere of aluminium of mass

0.20 kg

is heated up to

150 ° C

. Immediately, it is put into water of volume

150 cc

27^{o} C

kept in a calorimeter of water equivalent to

0.025 kg

. The final temperature of the system is

40^{o} C

. The specific heat of the aluminium is(take

4.2 Joule = 1 calorie

)

HARD

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Change of State

Explain the following temperature versus time graph:

Question Image

EASY

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Change of State

A steam engine intakes $50 g$ of steam at $100 ° C$ per minute and cools it down to $20 ° C$ . If latent heat of vaporization of steam is $540 cal g^{- 1}$ , then the heat rejected by the steam engine per minute is _____ $\times 10^{3} cal$

(Given : specific heat capacity of water : $1 cal g^{- 1} {{}^{\circ}C}^{- 1}$ )

EASY

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Change of State

A closed bottle containing water at

30^{o} C

is open on the surface of the moon. Then-

EASY

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Change of State

Latent heat of vaporisation of water is

22.6 \times 10^{5} J {kg}^{- 1}

. The amount of heat needed to convert

100 kg

of water into vapour at

100 ° C

MEDIUM

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Change of State

50 g

of ice at

0 ° C

is mixed with

50 g

of water at

80 ° C

. If the latent heat of ice is

80 cal g^{- 1}

and specific heat of water is

1 cal g^{- 1} ° C^{- 1}

, then the final temperature of mixture is

MEDIUM

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Change of State

A solid metal weighing

150 g

melts at its melting point of

800 ° C

by providing heat at the rate of

100 W

. The time taken for it to completely melt at the same temperature is

4 \min

. What is the specific latent heat of fusion of the metal?

EASY

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Change of State

The physical quantity that determines whether or not a given system

A

is in thermal equilibrium with another system

B

is called

HARD

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Change of State

A thermally insulated cubical box of side length $20 cm$ and wall thickness $2 cm$ containing $2 kg$ of ice is closed on all sides. The mass of ice melted in $10$ hours is (Thermal conductivity of the material of the box $= 0.01 {Wm}^{- 1} K^{- 1},$ latent heat of ice $= 360 \times 10^{3} J {kg}^{- 1}$ and ambient temperature $= 40 ° C$ )

HARD

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Change of State

10 H

inductor carries a current of

20 A

. If the energy stored in this inductor melts ice at

0 ° C,

then the mass of the ice melted is

[

Latent heat of ice

= 2.26 \times 10^{3} J {kg}^{- 1}]

EASY

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Change of State

Two systems are in thermal equilibrium. The quantity which is common for them is

MEDIUM

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Change of State

A thermally insulated vessel contains

150 g

of water at

0 ° C

. Then the air from the vessel is pumped out adiabatically. A fraction of water turns into ice and the rest evaporates at

0 ° C

itself. The mass of evaporated water will be closest to: (Latent heat of vaporization of water

= 2.10 \times 10^{6} J k g^{- 1}

and Latent heat of Fusion of water

= 3.36 \times 10^{5} J k g^{- 1}

)

EASY

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Change of State

If pressure increased on a piece of wax, the melting point of wax

MEDIUM

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Change of State

Steam at

100^{o} C

is passed into

20 g

of water at

10^{o} C .

When water acquires a temperature of

80^{o} C,

the mass of water present will be:
[Take specific heat of water

= 1 c a l g^{- 1 o} C^{- 1}

and latent heat of steam

= 540 c a l g^{- 1}]

EASY

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Change of State

Heat required to melt $1 g$ of ice is $80 cal$ . A man melts $60 g$ of ice by chewing in one minute. His power is______

MEDIUM

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Change of State

1 kg

of water, at

20 ° C

is heated in an electric kettle whose heating element has a mean (temperature averaged) resistance of

20 Ω .

The rms voltage in the mains is

200 V

. Ignoring heat loss from the kettle, time taken for water to evaporate fully is close to
[ Specific heat of water

= 4200 J {kg}^{- 1} ° C^{- 1}

Latent heat of water

= 2260 k J k g^{- 1}

]

EASY

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Change of State

A piece of ice falls from a height

h

so that it melts completely. Only one-quarter of the heat produced is absorbed by the ice and all energy of ice gets converted into heat during its fall. The value of

h

is:
(Latent heat of ice is

3.4 \times 10^{5} {J kg}^{- 1}

and

g = 10 {N kg}^{- 1}

)

MEDIUM

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Change of State

2 g of water condenses when passed through 40 g of water initially at 25

℃

. The condensation of steam raises the temperature of water to 54.3

℃

. What is the latent heat of steam?

MEDIUM

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Change of State

Amount of heat required to convert 10 g of ice to water at 20 $℃$ is

MEDIUM

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Change of State

30^{o} C

, a lead bullet of 50g, is fired vertically upwards with a speed of 840 m/s. The specific heat of lead is 0.02 cal/

g^{o} C

. On returning to the starting level, it strikes to a cake of ice at

0^{o} C

. Calculate the amount of ice melted (Assume all the energy is spent in melting only)

What is latent heat?

Important Questions on Thermal Properties of Matter

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