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## CHANGES IN THE STATE OF MATTER

Change in the state of matter is accomplished when the temperature of solid is increased.

The particles acquire sufficient energy to disrupt the ordered arrangement of the molecules and convert to the liquid state. As the temperature is further increased the distance between the molecules is enormously increased and resulted in the free movement of the molecules and pass into the gaseous state.

Various physical phenomenons are occurred during the change in the state of matter due to change in entropy and the enthalpy. They are as follows:

﻿﻿﻿Melting: When a solid turns to liquid due to increase in temperature.

﻿﻿﻿Freezing: When a liquid turns to solid due to decrease in temperature.

﻿﻿﻿Vaporization: When liquid turns to vapours due to increase in temperature.

﻿﻿﻿Condensation: when vapours turns to liquid due to decrease in temperature.

﻿﻿﻿Sublimation: when the solid turns to gas without passing through the intermediate liquid phase at the temperature and pressure below the substance's triple point.

﻿﻿﻿Deposition: The reverse of sublimation is called the deposition i.e., conversion of gas to solid.

While conversion from solid to liquid and from liquid to gas state, the enthalpy (heat content) of the material is also increased. Thus enthalpy of liquid is greater than the solid and the enthalpy of gas is greater than that of liquid. Similarly, entropy (degree of molecular randomness) also increase with the conversion from solid to liquid and then to gas.

### LATENT HEAT

When change in the state of mater occurs, temperature does not rise, it remains constant but heat get absorbed or liberated. Thus, the heat which results in the change of matter, 9r without change in the temperature is called the latent heat.

Latent heat of Fusion:

This heat is latent because it is not associated with the change in temperature. Latent heat of fusion is associated with the solid-liquid transition without change in the temperature.

For example, ice (at 0°C or 32°F) converts to water with the latent heat of fusion.

Ice (at 0°C) converts to water with the latent heat of fusion. The heat of fusion for water at 0°C is approximately 80 calories per gram of ice.

Latent heat of vaporization:

Latent heat of vaporization is associated with liquid-vapour transition. The amount of heat required to convert unit mass of a liquid into the vapour without a change in temperature.

The latent heat of vaporization of water at 100°C is approximately 533 calories per gram of liquid.

### VAPOUR PRESSURE

There is a tendency of liquid to evaporate constantly. It takes place at the surface of the o liquid. The liquid molecules escape into the space above the surface when kinetic energy of liquid molecules overcomes the intermolecular forces of attraction in the liquid state.

This process is called 'evaporation'. If evaporation is carried out in a closed container system then the vapors of liquid remains in contact with surface of the liquid and accomplish continuous random motion. During this motion, molecules collide with each other and also with walls of the container. Due to this activity, molecules losses their energy and returns back to liquid state. This process is called as 'condensation'.

The phenomenon of evaporation and condensation is a constant process and after some time equilibrium is established at constant temperature between evaporation and the condensation. At equilibrium number of molecules in vapor state remains constant at constant temperature.

Thus, the pressure exerted by vapors of liquid on the surface of liquid when equilibrium is established between liquid and its vapor is called vapor pressure of the liquids. The vapor pressure of liquid depends on nature of the liquid and the temperature. The vapor pressure of liquid decreases with the increase in the intermolecular forces of attraction but it increases with the increase in the temperature. Vapor pressure can be measured in different units' viz., (kPa (kilo pascal), atm, bar, mm Hg, torr).

Que. Define matter. Classify matter on the basis of its state.
Ans.

Matter: Matter can be defined as a substance that has a mass and that requires space. The matter is made up of infinitesimally small atoms, which are in a continuous state of motion.

Classification of matter on the basis of state:

Matter can be classified on the basis of state into three categories :

Gas: It consists of molecules separated wide apart in empty spaces. These molecules are free to move in the container.

(ii) Liquid: The molecules in a liquid are comparatively closer to each other than gaseous molecules. They also have the freedom of movement within the system.

(iii) Solids: The molecules, atoms or ions are arranged in a certain order in fixed positions in the crystal lattice. They however do not have the freedom of movement.

Que. How the Changes occur in the states of matter?
Ans.

Changes in the States of matter:

•  Changes can occur in the states of matter either by heating or cooling. It can result in a physical or chemical change.

Physical change is that when only the state of the substance changes, without any change in the chemical composition.

• ﻿﻿The process in which solid changes to a liquid is called as melting.
• ﻿﻿The process in which liquid changes to a solid is called as freezing.
• ﻿﻿The process in which liquid changes to a vapour is called as evaporation.
• ﻿﻿The process in which vapour changes to a liquid is called as condensation.
• ﻿﻿The process in which solid changes to a vapour is called as sublimation.
• ﻿﻿Chemical change occurs when a substance changes into a new substance. It is indicated by change in the density, melting point of the original substance.
Que. What do you understand by vapour pressure? Discuss factors affecting it.
Ans.

Vapour Pressure:

﻿﻿When a liquid is placed in an open vessel, it evaporates. The molecules of a liquid move with different kinetic energies. Those molecules which possess higher kinetic energies manage to overcome the intermolecular forces holding them in a liquid and thus escape from the liquid surface as vapours. The process by which the molecules of a liquid go into the gaseous state is called vaporisation or evaporation.

﻿﻿If the liquid is placed in a closed vessel, the vapours escape into the empty spaces above the liquid but as the concentration of the liquid molecules in the empty spaces increases the molecules strike on the walls of the vessel and get converted back into liquid. This process is called as condensation. Thus a dynamic equilibrium is established between the liquid and vapour at a given temperature. Now the concentration of the vapour in. the space above the liquid remains unchanged with the lapse of time. This vapour will exert a definite pressure at equilibrium. The pressure exerted by the vapour in equilibrium with the liquid is called as vapour pressure.

Factors affecting vapour pressure:

Factors affecting vapour pressure are discussed as follows:

Nature of the liquid: The vapour pressure exerted by a liquid depends on its nature. Liquids with a low boiling point will have a high vapour pressure.

﻿﻿﻿Intermolecular forces of attraction: Liquids with weak intermolecular forces of attraction evaporate faster and then have a high vapour pressure.

﻿﻿﻿Temperature: If the temperature of the liquid increases, the vapour pressure also increases. An increase, in temperature increases the kinetic energies of more molecules and hence more of them leave the liquid thereby increasing the vapour pressure.

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Changes of State | Matter | Physics | FuseSchool On Earth, materials exist in one of three main states of matter: solid, liquid or gas.

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##### ADSORPTION AND SURFACTANTS (SURFACE ACTING AGENTS)
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