It is the state of matter in which atoms are tightly bonded to each other and occupy fixed positions, giving substances a definite shape. Molecules are tightly packed with one another as they can vibrate about a fixed position. The particles cannot slip or slide over one another, therefore, they have definite shape and volume.
Fusion is the combination of two or more atoms, molecules, or nuclei to form heavier and bigger molecules or nuclei.
This process of conversion of a liquid to a gas or vapor at all temperatures is called evaporation. It is a continuous process. The greater surface area exposed increases the rate of evaporation. For example, a wet cloth spread out dries faster than when it is folded.
Conversion of solid into a gas without going to a liquid state, during heating is called sublimation.
Q.2) What do you mean by liquid? Describe the interchange of liquid to gas.
In this state, molecules are not tightly packed. Their positions are not fixed so they can move freely in all directions. Due to this liquids do not have any definite shape. They can acquire the shape of a vessel. In a liquid state, the kinetic energy of molecules is less than the gaseous state. Therefore intermolecular forces are stronger than gaseous states. Thus liquid has a fixed volume.
Interchange of liquid to gas
Liquids can be converted into gases. When liquid is heated the kinetic energy of liquid molecules increases. Due to an increase of kinetic energy, certain molecules start escaping from the surface of the liquid and this escape of molecules is called evaporation. At a certain temperature, the vapor pressure becomes equal to external pressure and at this temperature, the liquid starts boiling. At this point, vapor bubbles leave the surface of the liquid and are converted into gas. At boiling point, the temperature of the liquid remains the same until all the liquid is evaporated or vaporized through heat.
Q.3) How solid is converted into liquid? Explain it.
When a solid is heated, then the kinetic energy of particles increases and it becomes hot. If heating is continued then at a certain temperature, the added energy becomes enough to overcome the attractive forces holding particles of solid in their fixed positions and it starts melting.
The temperature at which a solid starts melting is called the melting point. At this point solid particles lose their fixed positions as well as their arrangements and thus solid is converted into liquid. At the melting point, the temperature of solid and liquid remains the same until all the solid is melted through heat. It means in this condition the rise in temperature is used in the change of state from solid to liquid and this change is called fusion.
Q.4) What is diffusion? Explain on the basis of kinetic molecular theory.
The spreading of a substance through a medium like air or liquid is called diffusion. The rate of diffusion depends upon its molar mass or density.
In 1846 a Scottish chemist, Thomas Graham presented Graham’s law of diffusion. On the basis of kinetic molecular theory, this law states that the rate of diffusion of a gas is inversely proportional to the square root of its molar mass or density. Lighter gases can diffuse faster than heavier gases.
For example, hydrogen is a lighter gas than oxygen as hydrogen’s molar mass is less than that of oxygen. So as by law, hydrogen gas diffuses four times faster than oxygen gas under the same conditions.
Q.5) What is the Brownian movement? Describe a suitable example.
A continuous, rapid, zig-zag motion of suspended particles through the medium is called Brownian motion.
This property was first observed by British Botanist Robert Brown in 1827 when he was observing the movement of pollen grains in water by microscope. He observed and concluded that if the particles are suspended in liquid drops then these particles are not at rest but they are moving in all directions in a zigzag motion.
For example, mix some powdered sulfur in the water and stir it. This mixture is filtered through filter paper. Some of the small particles of sulfur pass through the filter paper into the filtrate. Now take a drop of this filtrate under the microscope and examine it. It is observed that sulfur particles show rapid, random, and zigzag movement through the medium. This motion is called the Brownian movement.
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