Matter In Our Surroundings

On raising the temperature, the kinetic energy of the particles increases. Due to this, the particles overcome their forces of attraction and are able to move freely. Hence, the rate of evaporation, diffusion and expansion of gases increases on raising the temperature.

By reducing the temperature and by applying high-pressure gases can be converted into liquids. When pressure is applied to a gas at a reduced temperature, its molecules get closer. This helps to remove enough energy and changes the gas into a liquid state.

Gases and liquids behave like fluids because they can be made to flow or move. The molecules in any fluid are in constant, random motion, colliding with themselves and the walls of the container.

In an earthen pot, water gets evaporated through the pores quickly. Since some heat energy is taken from the water during the process of evaporation. Due to evaporation, the temperature of the remaining water is reduced.

The forces of attraction between the particles of a gas are minimum, intermediate in case of a liquid and are maximum in a solid. Hence, in case of oxygen ‘forces of attraction’ are minimum since it is a gas. In case of water being a liquid ‘forces of attraction’ are intermediate. In case of sugar, ‘forces of attraction’ are greater since it is solid.

Kelvin is the SI unit of temperature.
To change a temperature on the Kelvin scale to the Celsius scale, subtract 273 from the given temperature.
To convert a temperature on the Celsius scale to the Kelvin scale you have to add 273 to the given temperature.

Hence, 25°C+273= 298 K, 38°C+273= 311 K and 66°C +273= 339 K.

Sublimation is a physical process where solid changes directly into a gas without passing through the intermediate liquid phase. For example, solid carbon dioxide also known as Dry Ice changes into gas directly without passing through the liquid phase.

Kelvin is the SI unit of temperature. To change a temperature on the Kelvin scale to the Celsius scale you have to subtract 273 from the given temperature and to convert a temperature on the Celsius scale to the Kelvin scale you have to add 273 to the given temperature. Hence, 35°C+273=308 K, 56°C+273= 329 K and 118°C +273= 391 K. The boiling points of diethyl ether, acetone and n-butyl alcohol are 308 K, 329 K and 391 K respectively.

On increasing the temperature of water, the kinetic energy of the particles increases. Due to this, the particles overcome their forces of attraction and are able to move freely. Hence, results in the increase of evaporation of water.

Some hydrogen gas leaking out of the container will result in the availability of more free space for the remaining hydrogen molecules. Hence, the particles will be able to move more freely and the distance between them will increase. Increasing the volume of the container of hydrogen gas will also result in the increase of motion of particles. There will be more space available for the particles to move. As a result, the particles will move away from each other causing an increase in distance between them.

No, the water is not pure. It contains some non-volatile impurities dissolved due to which water boils at a temperature higher than normal boiling point. And, its freezing point will be below 0°C due to the presence of a non-volatile impurity in it.
Non-Volatile impurities are those substances which do not evaporate easily on boiling the liquid. Also, the presence of impurities lowers the vapour pressure of the original liquid which cause the lowering of freezing point of the liquid.

In the beginning, ice and water are in equilibrium, hence the temperature would be zero. On heating the mixture, the temperature remains the same till all the ice melts. This heat gets used up in changing the state by overcoming the forces of attraction between the particles. As this heat energy is absorbed by ice without showing any rise in temperature, it is considered that it gets hidden into the contents of the beaker and is known as the latent heat*. On further heating, the temperature of the water would increase. Therefore, the correct option is (d).

* Latent heat of fusion is the amount of heat energy required to change 1 kg of solid into liquid at its melting point.

(a) Evaporation of a liquid at room temperature leads to the cooling effect.

Since some heat energy is taken from the liquid during the process of evaporation. Due to evaporation, the temperature of the remaining liquid is reduced.

(b) At room temperature, the forces of attraction between the particles of solid substances are stronger than those which exist in the gaseous state.

The forces of attraction between the particles of a gas are minimum, intermediate in case of a liquid and are maximum in a solid. Hence, in case of oxygen ‘forces of attraction’ are minimum since it is a gas. On increasing the temperature of solids, the kinetic energy of the particles increases. Due to the increase in kinetic energy, the particles start vibrating with greater speed. The energy supplied by heat overcomes the forces of attraction between the particles. The particles leave their fixed positions and start moving more freely.

(c) The arrangement of particles is less ordered in the liquid state. However, there is no order in the gaseous state.

The forces of attraction between the particles of a gas are minimum, intermediate in case of a liquid and are maximum in a solid. Hence, in case of oxygen ‘forces of attraction’ are minimum since it is a gas.

(d) Sublimation is the change of gaseous state directly to solid state without going through the liquid state.

Sublimation is a physical process where solid changes directly into a gas without passing through the intermediate liquid phase. For example, solid carbon dioxide also known as Dry Ice changes into gas directly without passing through the liquid phase.

(e) The phenomenon of change of a liquid into the gaseous state at any temperature below its boiling point is called evaporation.

The particles of matter are always moving. In case of any gas, liquid or a solid at any given temperature particles have different kinetic energy. A small fraction of particles at the surface of a liquid has higher kinetic energy. Due to higher kinetic energy, these particles are able to break away from the forces of attraction of other particles and gets converted into vapour. This phenomenon of change of a liquid into vapours at any temperature below its boiling point is called evaporation.

The correct answers are following:

Correct answers are following:

Yes, this is true that Osmosis is a special kind of diffusion’. In both osmosis and diffusion, there is a movement of particles from a region of higher concentration to that of a lower concentration. However, in the case of ‘Osmosis,’ the solvent molecules pass through a semipermeable membrane from a dilute solution to more concentrated solution.
Examples:
Osmosis: Water flowing across the plasma membrane
Diffusion: Spraying perfume in a room

(a) The swelling up of a raisin on keeping in water is ‘Osmosis’ because the concentration of solutes in raisin is more than outside water. Hence, water moves inside the raisin causing the swelling up of raisin.

(b) The spreading of the virus on sneezing is Diffusion.

Due to sneezing, virus enters the air in the form of small droplets. They remain suspended in the air for a long time and move here and there in the air due to diffusion.

(c) The earthworm dying on coming in contact with common salt is ‘Osmosis’.
Earthworms die on coming contact with common salt because their skin dries out due to loss of water.

(d) The shrinking of grapes kept in thick sugar syrup is ‘Osmosis’.
This is because water will move down the concentration from higher concentration to lower concentration. this results in shrinkage of grapes.

(e) The Preserving pickles in salt is ‘Osmosis’. Salt helps to remove water from the cells and helps to preserve pickles.

(f) The spreading of the smell of cake being baked throughout the house is ‘Diffusion’. The particles of cake spread through diffusion hence, producing the smell.

(g) The aquatic animals using oxygen dissolved in water during respiration answer is ‘Diffusion’.
Aquatic animals use the oxygen dissolved in water through diffusion. The amount of dissolved oxygen also depends on temperature, amount of salts in water and pressure.

In case of ice the water molecules have lower energy. On contact with the skin, the water molecules absorb energy from the body. Thus, provided with a cooling effect. Whereas in the case of steam, the water molecules have higher energy. The high energy of water molecules in steam is transformed into heat and may cause burns.

Particles in steam, that is, water vapour at 373 K (100⁰ C) have more energy than water at the same temperature. This is because particles in steam have absorbed extra energy in the form of latent heat of vaporisation*. When steam tends to cool down, first steam condenses to water on skin and then water tends to cool down to the temperature of the skin. This is the reason why Alka felt intense heat from the puff of steam.
* Latent heat of vaporisation: When a liquid is changed into vapour phase, then the energy absorbed in this process is called the latent heat of Vapourisation. The heat of vaporization of water is about 2,260 kJ/kg.

The correct answer is (a). The temperature of the water in a tumbler will fall initially till it reaches 0 °C, the freezing point of water. After reaching the freezing point, the temperature will remain constant till all the water has been converted into ice. And, after this temperature would further decrease below 0 °C.

The correct answer is (c). In vessel,(c) the rate of evaporation will be he highest.
Evaporation is a surface phenomenon. The surface area of water in the (c) vessel and vessel (a) are the highest as compared to other containers. But, on vessel (c), the fan is attached, so the there is an increase in the air speed. Also, the particles move away due to increased air speed. As a result of this, the rate of evaporation will increase in vessel (c) than (a).

The term used to denote the conversion of vapour to solid is called Deposition. For example, in sub- freezing air, the water vapours changes directly into ice.

The amount of heat required to convert 1 kg of solid into liquid at one-atmosphere pressure at its melting point is known as its latent heat of fusion.

Naphthalene is insoluble in water but soluble in ether*. When this mixture is dissolved in water, naphthalene will remain insoluble and will be recovered at the bottom of the beaker. But it is volatile* at room temperature.
* Ether is an organic solvent that contains an oxygen molecule connected to two alkyl/aryl groups. Example: R-O-R^’ is an ether.
*Volatile: Any substance that can be easily evaporated at room temperature is called volatile substance.

Ammonium chloride is soluble in water and is volatile at higher temperatures i.e. it evaporates at higher temperature and not at room temperature. This mixture can then be decanted in the funnel fitted with filter paper. The filtrate then contains ammonium chloride dissolved in water. It decomposes on heating to dryness.

Priyanshi would feel more comfortable as she is wearing cotton clothes. Because of our body mechanism, we tend to perspire more during summers. This helps to keep our body cool. During evaporation, the particles at the surface of the liquid gain energy from the surroundings or the body surface and change into a vapour. The heat energy equal to the latent heat of vaporization is absorbed from the body leaving the body cool. Cotton, being a good absorber of water helps in absorbing the sweat and exposing it to the atmosphere and makes evaporation easy. Ali, on the other hand, is wearing nylon which is less efficient in absorbing water will not help with evaporation.
Therefore, Priyanshi will be more comfortable as compared to Ali because she wears cotton and Ali wears nylon.

To dry the shirt faster we should increase the rate of evaporation. Following are steps we can take to increase the conditions of evaporation:

(a) As we know that the evaporation is a surface phenomenon. We can spread the shirt such that to increase the surface area. This will help to speed up the evaporation process.

(b) By putting the shirt under the sun will increase the temperature which will further increase the evaporation.

(c) The process of evaporation can be further increased by putting it under the fan. This will move away from the particles of water vapour in the air, which will further increase the rate of evaporation.

(a) It is true that Evaporation produces cooling.
Evaporation is a surface phenomenon. Since some heat energy is taken from the surrounding during the process of evaporation. The particles of the liquid absorb energy from the surrounding to regain the energy lost during evaporation. This absorption of energy from the surroundings make the surroundings cold producing a cooling effect.

(b) Its true that the rate of evaporation of an aqueous solution decreases with increase in humidity.

The amount of water vapour present in the air is called Humidity. At a given temperature, the air around us cannot hold more than a definite amount of water vapour. If the amount of water in air is already high, the rate of evaporation decreases. As a result, the rate of evaporation of an aqueous solution decreases with increase in humidity.

(c) Yes, Sponge is a solid though it is compressible.
Sponge has a lot of small holes in it. Air is trapped inside these minute holes. When we press the sponge, air is expelled out and we can compress it. The sponge remains in that compressed shape until we apply force on it. When we release it, the air reoccupies its minute holes and the sponge regains its original shape.

1) The temperature of a substance remains constant during its melting point because this heat is used in changing the state of the substance by overcoming the forces of attraction between the particles in the existing state.
2) Example, when we heat ice, then the heat energy we supply is absorbed by ice without any rise in temperature. This is because, the heat absorbed in the contents of the beaker.
3) Similarly, the temperature of a substance also remains constant at its boiling point until the complete substance boils. When we supply heat energy to water, particles gain more kinetic energy and then they move faster. And, slowly, the particles overcome the forces of attraction and at this point, the liquid starts changing into gas at this point. This is called the boiling point