Important Points: Matter in Our Surroundings - Science Class 9

 What is Matter?

• Anything that occupies space and has mass is called matter.
• The matter is made up of small particles, which may be molecules, atoms, or ions.
• The matter commonly exists in three states, i.e., solids, liquids, and gases.
    Examples of Matter

Characteristics of Particles of Matter

• The particles of matter are always in a state of motion and, hence, possess kinetic energy. The kinetic energy is minimum in solids, intermediate in liquids, and maximum in gases.
• The particles of matter attract each other with intermolecular force, which is maximum in the case of solids, less in the case of liquids, and less in the case of gases.
• The spaces in between the particles of matter are called intermolecular spaces. They are least in the case of solids, more in the case of liquids, and maximum in the case of gases.
• The lesser the intermolecular spaces between the molecules, the more the intermolecular forces.

States of Matter

• In the case of solids, the intermolecular spaces and the kinetic energy of the molecules are the least, but the intermolecular forces are the maximum.
• In the case of liquids, the intermolecular spaces and the kinetic energy of the molecules are more than that in the solids, but the intermolecular forces are less than that in solids.
• In the case of gases, the intermolecular spaces and the kinetic energy of the molecules are maximum, and the intermolecular forces are minimum.
• The arrangement of particles is most ordered in the case of solids, in the case of liquids, layers of particles can slip and slide over each other, while for gases, there is no order, particles move about randomly.

Change in States of Matter

• The states of matter are interconvertible and can be changed by changing the temperature and pressure.
• Sublimation is the change of state from solid to gas without going through the liquid state on heating and vice versa.
  
• Fusion or melting is the change of state from solid to liquid, and the temperature at which it occurs is called the melting point.
• Vaporization or boiling is the change of state from liquid to gas; the temperature at which it occurs is called the boiling point.
• Boiling is a bulk phenomenon. Particles from the bulk (whole) of the liquid change into a vapor state.

Evaporation

• Evaporation is a surface phenomenon. Particles from the surface gain enough energy to overcome the forces of attraction present in the liquid and change into the vapor state.
• The rate of evaporation depends upon the surface area exposed to the atmosphere, the temperature, the humidity, and the wind speed. Evaporation causes cooling.
• Latent heat of vaporization is the heat energy required to change 1 kg of a liquid to gas at atmospheric pressure at its boiling point.
• The latent heat of fusion is the heat energy required to change 1 kg of solid into liquid at its melting point. 

Density: The mass of a substance per unit of volume, i.e., density = mass/volume.
SI unit of density is kg m^-3  

Volume: All solids occupy a fixed volume. The shape occupied by a substance is called volume.

The unit of volume is m³ (cubic meter). The common unit of volume is L (liter).

1m³ = 1000 dm³ = 1000 L 
1 L = 1 dm³ 
1 L = 1000 ml = 1000 cm³

Frequently Asked Questions (FAQs)

1. What is matter? 

Ans. Matter refers to anything that occupies space and has mass. It can exist in various forms, such as solid, liquid, or gas.

2. What are the characteristics of particles of matter? 

Ans. The characteristics of particles of matter include:

• Particles of matter are continuously moving and possess kinetic energy.
• They have intermolecular forces of attraction between them.
• The particles have space between them, known as interparticle spaces.
• The particles are constantly colliding with each other and the walls of the container they are in.

3. What are the different states of matter? 

Ans. The different states of matter are:

•  Solid: In this state, particles are closely packed together and have a fixed shape and volume.
• Liquid: In this state, particles are loosely packed, allowing them to flow and take the shape of the container they are in. They have a fixed volume.
• Gas: In this state, particles are far apart and move freely, filling the entire space available to them. They have neither a fixed shape nor a fixed volume.

4. What is evaporation? 

Ans. Evaporation is the process by which a liquid changes into a gas at a temperature below its boiling point. During evaporation, particles at the surface of a liquid gain enough energy to overcome intermolecular forces and escape into the surrounding space as vapor.

5. Why is evaporation considered a cooling process? 

Ans. Evaporation is considered a cooling process because it requires energy. When particles evaporate from the surface of a liquid, they take away energy in the form of heat from the remaining liquid particles. This results in a decrease in the average kinetic energy of the remaining particles, leading to a decrease in temperature and a cooling effect.