In a pressure cooker the cooking is fast because.

Cooking is fast in pressure cooker just because the trapped steam increases the atmospheric pressure inside the cooker. At that pressure, boiling point of water is increased and this higher temperature cooks food faster.

Latent heat of fusion of ice is:

Latent heat of fusion of ice\\(=80 cal g^{-1}\\)\\(=80\times 4.2 J\times 10^3 kg^{-1}\\)\\(=336\times 10^3 J kg^{-1}\\)

Define latent heat of vaporization.

Latent heat of vapourisation is a physical property of a substance. When a material in liquid state is given energy, it changes its phase from liquid to vapour without change in temperature, the energy absorbed in the process is called latent heat of vaporization. The latent heat of vaporization of water is about \\(2260kJ/Kg\\) which is equal to \\(40.8kJ/mol\\).

How much heat energy is gained when 5 kg of water at \\(20 ^ { \circ } \mathrm { C }\\) is brought to its boiling point?

\\(Q = mc\Delta \theta \\)\\( = 5 \times \left( {1000 \times 4.2} \right) \times \left( {100 - 20} \right)\\)\\( = 1680 \times {10^3}J\\)\\( = 1680\,KJ\\)Hence,option \\((A)\\) is correct answer.

What is the effect of increase in pressure on the boiling point of a liquid ?

As the pressure applied to the liquid surface is increased, the energy needed for the liquid molecules to expand to gas phase also increases. Hence, a higher temperature is required to change liquid to gas phase. So, boiling point of liquid rises on increasing pressure.

You are provided with a mixture of naphthalene and ammonium chloride by your teacher. Suggest an activity to separate them with well labelled diagram.

Napthalene is insoluble in water but soluble in benzene (organic solvent). Ammonium chloride is soluble in water but insoluble in benzene. Napthalene changes into vapours at room temperature whereas ammonium chloride changes into vapours on heating. Method :(a) Add water to the mixture and shake it vigorously to dissolve ammonium chloride.(b) Filter the mixture. Napthalene is obtained as residue whereas, filtrate contains ammonium chloride. Crystallize the filtrate by heating till saturated solution of ammonium chloride is obtained.(c) Cool the hot saturated solution to get crystals of ammonium chloride.

Give a reason for the following observations:\\((a)\\) Naphthalene balls disappear with time without leaving any solid.\\((b)\\) We can get the smell of perfumes sitting several metres away.

(a) Naphthalene balls undergo sublimation due to which it converts directly into vapours and disappear into air without leaving any solid.(b) The particles of perfume diffuse rapidly into the air and its smell can be felt while sitting several metres away.

The average thermal energy for a mono-atomic gas is : (\\(k_B\\) is Boltzmann constant and \\(T\\), absolute temperature)

The average thermal energy for the mono-atomic gas is given by:\\(E=\dfrac32 k_BT\\)

Advanced Knowledge of Change of State | Definition, Examples, Diagrams

definition

Sublimation

Sublimation is the transition of a substance directly from the solid to the gas phase without passing through the intermediate liquid phase.

definition

Sublimation

Sublimation is the transition of a substance directly from the solid to the gas phase without passing through the intermediate liquid phase.
Examples is ammonium chloride when heated changes from solid to gas.Even camphor and dry ice undergo sublimation.

definition

Boiling point and normal boiling point

The boiling point of a substance is the temperature at which the vapour pressure of the liquid equals the pressure surrounding the liquid and the liquid changes into a vapour at STP.The normal boiling point (also called the atmospheric boiling point or the atmospheric pressure boiling point) of a liquid is the special case in which the vapour pressure of the liquid equals the defined atmospheric pressure at sea level, 1 atmosphere.

definition

Factors affecting boiling point

Pressure: If the external pressure is higher than one atmosphere, the liquid will boil at a higher temperature than the normal boiling point.
Molecule Types: Types of molecules in the liquid affect the boiling point of the liquid. If the force of attraction between the molecules is relatively strong, the boiling point will be relatively high. If the force of attraction between molecules is relatively weak, the boiling point will be relatively low.

definition

Boiling point and melting point of different substances

The boiling point is the temperature at which a material changes from a liquid to a gas (boils).
Here are boiling point of different substances:
pentane

(3 6^{0} C)

, Bromine

(58 . 5^{0} C)

, Water

(10 0^{0} C

etc.
The melting point of a solid is the temperature at which it changes state from solid to liquid at atmospheric pressure.
Here are melting point of different substances:
mercury

(38.8 3^{0} C)

, water

(0^{0} C)

Aluminum

(60 0^{0} C)

etc.

definition

Experimentally define melting point of ice

Here is the procedure to determine the melting point of ice:
1. Take some ice cubes and dry them using a filter paper and quickly put them in a beaker.
2. Place the beaker over a wire gauze kept over a tripod stand.
3. Suspend a thermometer (temperature range -10 to 110C) with the help of a clamp stand so that its bulb remains in the middle of the ice cubes.
4. Ice cubes are moderately heated by a gas burner and stirred continuously using a glass rod.
5. Note the temperature

(t_{1})

when the ice starts melting.Continue heating the ice.
6. Note the temperature

(t_{2})

when the ice has melted completely.
7. Record your observations in tabular form

t_{1}

in one column and

t_{2}

in another column.Now find the average of

t_{1}

and

t_{2}

which will give you the melting point of ice.

definition

Experimentally define boiling point of water

Here is the procedure for finding the boiling point of water :
1. Take about

25 m l

of distilled water in a boiling tube and add

2 - 3

small pieces of pumice stone.
2. Close the mouth of the boiling tube with a rubber cork that has two bores and clamp it with the stand.
3. Introduce a thermometer (temperature range

- 10 t o 110 C

) in one bore of the cork of the boiling tube. Keep the bulb of the thermometer about

3 - 5 c m

above the surface of the water.
4. Then introduce one end of a delivery tube in the second bore of the cork.Place a

250 m l

beaker below the second end of the delivery tube to collect the condensed water.
5. Heat the boiling tube gently, preferably by rotating the flame.
6. Note the temperature

(t_{1})

when the water starts boiling.
7. Continue to heat the water till the temperature becomes constant, and the water remains boiling. Note the constant temperature

(t_{2})

.
8. Record your observations in tabular form

t_{1}

in one column and

t_{2}

in another column.Now find the average of

t_{1}

and

t_{2}

which will give you the boiling point of water.

Advanced Knowledge of Change of State

definition

Sublimation

definition

Sublimation

definition

Boiling point and normal boiling point

definition

Factors affecting boiling point

definition

Boiling point and melting point of different substances

definition

Experimentally define melting point of ice

definition

Experimentally define boiling point of water

Quick Summary With Stories

Heating Curve of Conversion of Ice to Steam

Sublimation

When $0.15 k g$ of ice at $0^{o} C$ is mixed with $0.30 k g$ of water at $5 0^{o} C$ in a container, the resulting temperature is $6 . 7^{o} C$ . Calculate latent heat of melting of ice.
(Specific heat of water is $4.186 \times 1 0^{3} J K g^{- 1}$ ).

In a pressure cooker the cooking is fast because.

Latent heat of fusion of ice is:

Define latent heat of vaporization.

How much heat energy is gained when 5 kg of water at $2 0^{\circ} C$ is brought to its boiling point?

What is the effect of increase in pressure on the boiling point of a liquid ?

You are provided with a mixture of naphthalene and ammonium chloride by your teacher. Suggest an activity to separate them with well labelled diagram.

Give a reason for the following observations:

$(a)$ Naphthalene balls disappear with time without leaving any solid.
$(b)$ We can get the smell of perfumes sitting several metres away.

The average thermal energy for a mono-atomic gas is : ( $k_{B}$ is Boltzmann constant and $T$ , absolute temperature)

definition

Sublimation

definition

Sublimation

definition

Boiling point and normal boiling point

definition

Factors affecting boiling point

definition

Boiling point and melting point of different substances

definition

Experimentally define melting point of ice

definition

Experimentally define boiling point of water

Quick Summary With Stories

Heating Curve of Conversion of Ice to Steam

Sublimation

When 0.15kg of ice at 0oC is mixed with 0.30kg of water at 50oC in a container, the resulting temperature is 6.7oC. Calculate latent heat of melting of ice. (Specific heat of water is 4.186×103JKg−1).

In a pressure cooker the cooking is fast because.

Latent heat of fusion of ice is:

Define latent heat of vaporization.

How much heat energy is gained when 5 kg of water at 20∘C is brought to its boiling point?

What is the effect of increase in pressure on the boiling point of a liquid ?

You are provided with a mixture of naphthalene and ammonium chloride by your teacher. Suggest an activity to separate them with well labelled diagram.

Give a reason for the following observations: (a) Naphthalene balls disappear with time without leaving any solid.(b) We can get the smell of perfumes sitting several metres away.

The average thermal energy for a mono-atomic gas is : (kB​ is Boltzmann constant and T, absolute temperature)

When $0.15 k g$ of ice at $0^{o} C$ is mixed with $0.30 k g$ of water at $5 0^{o} C$ in a container, the resulting temperature is $6 . 7^{o} C$ . Calculate latent heat of melting of ice.
(Specific heat of water is $4.186 \times 1 0^{3} J K g^{- 1}$ ).

How much heat energy is gained when 5 kg of water at $2 0^{\circ} C$ is brought to its boiling point?

Give a reason for the following observations:

$(a)$ Naphthalene balls disappear with time without leaving any solid.
$(b)$ We can get the smell of perfumes sitting several metres away.

The average thermal energy for a mono-atomic gas is : ( $k_{B}$ is Boltzmann constant and $T$ , absolute temperature)