Question

Chemistry notes for 9th class chapter 1​

Answer 1

Notes of chapter 1

Matter - matter is any physical substance that occupies space and possesses mass known as matter.

• Matter can be classified into solid, liquid, and gas-based on forces between the particles and the arrangement of particles
• solids have a very strong intermolecular force and very less space between the particles, have definite shape and volume, solids cannot flow, and these cannot be compressed, and have high-density melting and boiling point
• whereas liquids can flow and cannot be compressed, have the force of attraction between the particles stronger than gases and weaker than gas have a large intermolecular space, not a definite shape but have a definite volume
• gases have maximum intermolecular space and minimum intermolecular attraction and do not have a fixed shape, size, volume
• Effect of change of temperature on state of matter
• At increasing temperature, the kinetic energy of the particles of the matter increases. Therefore, the interparticle force of attraction between the particles reduces and particles move far from their position and begin to move freely.
• As a result, the state of matter changes
• Solids change to liquids.
• Similarly, liquids also change to form gases.
• The phenomenon by which molecules in a liquid state change to the gaseous phase at any temperature below their boiling point is called evaporation
• Factors affecting evaporation
• Humidity: The rate of evaporation decreases with an increase in humidity.
• Surface area: The rate of evaporation increases with an increase in surface area.
• Temperature: The rate of evaporation increases with an increase in temperature
• Wind speed: The rate of evaporation increases with an increase in wind speed Cooling due to evaporation
• During evaporation, the particles of a liquid absorb energy from the surroundings to overcome the inter-particle forces of attraction and undergo a phase change. The absorption of heat from the surroundings makes the surroundings cool.
• For example, sweating cools down our body and water gets cool in a water pot.

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Answer 2

Explanation:

Matter

Anything that has mass and takes up space is known as matter.

Example: Hydrogen, oxygen, sugar, sand, air, water, etc.

States of Matter

Matter can be classified into three types on the basis of intermolecular forces of attraction and the arrangement of the particles which are as follows.

• Solid: Solids have fixed shape and definite volume, they are hard to compressed, they are not able to flow and density is maximum. Solids have strong intermolecular attraction between particles.
• Liquid: Liquids have no fixed shape but have definite volume, they are easy to compressed as compared to solids, they are able to flow and density is medium. Liquids have intermediate intermolecular forces of attraction between particles.
• Gas: Gas don't have any fixed shape and definite volume, they are very easy to compressed, they can flow easily and have lowest density. Gases have weak intermolecular forces of attraction between particles.

These three forms of matter are inter-convertible by increasing or decreasing the pressure and temperature.

Example: Ice can be converted from solid to a liquid form by increasing the temperature and from water to vapour. Similarly, vapour change into liquid form by decreasing the temperature and from liquid to ice.

Melting Point

Melting point is defined as the temperature at which solids melts and change into liquid form.

Example: Ice melts at 100°C to form water.

Boiling Point

The boiling point is defined as the temperature at which the vapour pressure of the liquid is equal to the atmospheric pressure.

Example: Water change into water vapour.

Sublimation

Sublimation is a process in which a substance directly changes its form from solid to gas without changing into liquid form.

Example: Burning of incense sticks

Evaporation

Evaporation is a process in which molecules in liquid state undergo a spontaneous transition to the gaseous phase at any temperature below its boiling point.

Example: Drying of wet clothes

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