Matter in Our Surroundings Class 9 Science Chapter 1
Topics taught
Effect of temperature: On increasing the heat, the particles gain energy and start vibrating with greater energy. Due to increased kinetic energy the particles overcome the force of attraction and a new state is obtained.
Effect of change of pressure on the matter: On applying pressure, the particles of matter can be brought close together and the state of matter can be changed. For example, CO2 gas can be solidified by applying pressure and lowering temperature.
Evaporation: The phenomenon of changing of a liquid into its vapour state at any temperature below its boiling point is called evaporation. Evaporation is a surface phenomenon.
Effect of Change of Temperature
What happens to matter when we heat it?
1. Solids:
As we heat solids, the kinetic energy between the particles of solids increases which decreases the force of attraction between them.
They start vibrating and changing their positions. Slowly, due to heat the particles become free and a solid converts into liquid.
Melting Point – The temperature at which solid melts to become a liquid at atmospheric pressure. For Example, the melting point of ice is 273.16 Kelvin.
Fusion – The process of melting of a solid into liquid is called Fusion.
Effect of Change of Temperature
In the melting process, once a solid reaches its melting point, its temperature does not increase further. So where does all the heat go? The heat present in the solid at time of melting is used by the particles to diminish the force of attraction between each other. The heat energy is therefore considered as hidden.
Latent Heat – The heat energy which is used to break the force of attraction between the particles of matter is known as latent heat. Since the heat is hidden therefore it is called as Latent Heat.
Latent Heat of Fusion – The amount of heat energy required to change 1 kg of a solid into liquid at atmospheric pressure at its melting point is known as the Latent Heat of Fusion.
Atmospheric Pressure – Pressure exerted by the weight of the atmosphere.
2. Liquids:
Just like in solids, the kinetic energy of particles of liquid increases, the force of attraction among them decreases and they start moving freely.
As we keep on supplying the heat, a point comes when the particles overcome the forces of attraction completely.
This is when a liquid starts changing into gas.
Energy from a stove heats up liquid water and creates steam
Boiling Point - The temperature at which a liquid starts boiling at the atmospheric pressure is known as its Boiling Point. For Example, The boiling point of water is 373 Kelvin.
Latent Heat of Vaporization – the amount of heat energy required to change 1 kg of a liquid into a gas at atmospheric pressure at its boiling point is known as Latent Heat of Vaporization
1. Gases:
The kinetic energy between the particles decreases and they turn into a liquid state.
Condensation / Liquefaction – The process of converting a gas into a liquid by cooling down its temperature. For Example, The formation of clouds is due to condensation of water vapor from Earth.
2. Liquids:
The kinetic energy between the particles decreases and they turn into a solid state. For Example, The formation of ice.
Sublimation – change of state of a gas directly into solid and vice-versa is known as sublimation. For Example, Camphor is a solid that directly evaporates into the air without changing to a liquid state.
Therefore, by increasing or decreasing the temperature we can change the states of matter into one another. Here is a diagram that sums this up.
Home work
1. Why do the gases exert more pressure on the walls of the container than the solids?
2. Which of the following diffuses faster?
Water vapour, wax or, ethyl alcohol.
