Class 9 science chapter 1 is the the foundational topics of Science, not only as a subject in board examination but also as an academic discipline to be pursued in higher studies, are introduced in class 9. It is on these basic concepts that advanced topics will be based on. Details explanation of this chapter already uploaded as a video format available on YouTube you can watch for better understanding.
Matter: The material made from which every object in the world is called matter. Objects that have mass and occupy space are called matter.
Matter is made up of Particles
All matter is made up of small particles. These particles are so small that they cannot be seen with the naked eye. Example: When a few drops of Dettol is added to a glass of water, it turns the entire water milky in colour, this action indicates that the substance is made up of microscopic particles, i.e. a few drops of Dettol in a glass of water It gets divided into as many parts as there are particles and mixes with all the particles, so you can guess how small the particles of matter are.
Characteristics of Particles of Matter
(i) There is empty space between the particles of matter : Matter is made up of microscopic particles and there is empty space between those particles. When salt or sugar is dissolved in water, it dissolves in water. This happens because the tiny particles of salt or sugar get incorporated into the empty spaces between the tiny particles of sugar. Are. It shows that the particles of matter have blood space.
(ii) Particles of matter are in constant motion :– Particles of matter are in constant motion, that is, they have kinetic energy. The speed of the particles increases with the increase in temperature, so we can say that the kinetic energy of the particles also increases with the increase of temperature. When a small piece of potassium permanganate is put in water, potassium permanganate in the form of fibers comes out of that piece. Permanganate slowly dissolves in water, indicating that the particles of the substance are in constant motion.
(iii) Particles of matter attract each other :- A force acts between the particles of matter which keeps the particles of matter together. The strength of this force of attraction between the particles of matter varies from substance to substance. This force of attraction between the particles of some substances is very high and this force of attraction between the particles of some substances is very less. Matter is hard or soft because of the strength or weakness of the force of attraction between its particles.
Iron is very hard, whereas a piece of chalk is not. It takes a lot of force to break a piece of iron, whereas a piece of chalk can be easily broken. This happens because the force of attraction between iron particles is very strong and the force of attraction between chalk particles is very weak.
States of Matter
There are three states of matter, These stages are:
Solid State:– Substances which have a definite shape, clear boundaries and constant volume are called solids or are said to be in solid state. Example: iron, coal, pot, chair, table, etc.
Properties of Solids:
- They have definite shape and clear boundaries.
- Fixed volume means compressibility is negligible.
- A solid maintains its shape even when an external force is applied.
- The intermolecular forces are greater in solids than in liquids and gases.
Liquid State: – Those substances which have indefinite shape and fixed volume are called liquid. Example: water, oil, milk, etc.
properties of liquids
- Liquid does not have a definite shape.
- They have a definite volume.
- Fluids flow and their shape keeps on changing.
- their intermolecular force is less than solid
Gaseous State:- The Substances which don’t have definite shape and volume are called gases, for example: air, oxygen, nitrogen, smoke, etc.
Properties of Gas:
- The compressibility of gases is much higher than that of solids and liquids.
- The intermolecular forces between their particles are the least.
- Gases can be easily pressurized.
- They diffuse very rapidly.
Comparison of the spaces between particles of different states of matter
Gas > Liquid > Solid
Change in state of matter
The change in the state of matter is due to the following:
- A decrease or increase in the space between particles can bring about a change in state.
- If the mobility of the particles of matter is increased or decreased, then the state can be brought about.
- If the force of attraction between the particles of matter is increased or decreased, then the change in the state of matter. It is known from all the above points that the change in the states of matter is due to the change in their different properties.
Physical factors that cause changes in the properties of matter that result in change of state
- Temperature: Temperature effect can cause a solid substance to change its states. Due to increase in temperature, a solid changes into a liquid and a liquid changes into, or can be changed into, a gas. And due to the decrease in temperature, gas can be converted into liquid and liquid into solid. In any case, on increasing the temperature the kinetic energy of the particles of matter increases. Due to increase in kinetic energy, the particles start vibrating with more speed. The energy provided by the heat overcomes the force of attraction between the particles, due to the particles leave their fixed positions and start moving more freely. Then a stage comes when the solid melts and turns into a liquid.
- Pressure: We have come to know that the state of a substance changes by increasing or decreasing the distance between the particles of a substance. If the state of a substance is to be changed, then pressure also does the same thing. An increase or decrease in pressure causes a change in the state of matter. For example, by compressing (pressurizing) the gas filled in the cylinder, a large amount of gas is filled in liquid form in a small cylinder. Temperature and pressure are responsible for bringing about a change in the state of matter.
Evaporation: A process in which surface particles in liquid substances begin to vaporize at any temperature below the boiling point. Such process is called evaporation.
The process of Evaporation
The particles of matter are always in motion and never stop. At a given temperature the particles of liquid or gas have different amounts of kinetic energy. In liquids, some fraction of the particles on the surface have enough kinetic energy that they break free from the force of attraction of other particles, and slowly vaporize.
Boiling Point: At atmospheric pressure, the temperature at which a liquid starts boiling, that temperature is called the boiling point of that liquid like: Water starts boiling at 373K i.e. 100 °C temperature, so the boiling point of water is 373 K
Melting Point: The temperature at which a solid melts to become a liquid is called the melting point of that solid. Example: The melting point of ice is 273.16K. That is, ice starts melting at a temperature of 273.16 K.
Latent Heat: When a substance reaches its melting point during the process of melting, even after increasing the temperature, it keeps changing the state of the substance without showing any increase in temperature, such that the thermal energy is stored by the substance. caused by absorption. This heat remains hidden in the substance and vessel, it is called latent heat.
Latent heat of fusion
The amount of heat energy required to convert 1 kg of solid into liquid at atmospheric pressure at its melting point is called latent heat of fusion.
For example, the energy of water particles at 0 °C (273 K) is greater than the energy of ice particles at the same temperature. Because the energy of water particles is its latent heat of fusion. absorbed by water particles
Latent Heat of Evaporation
The amount of heat energy required to vaporize 1 kg of liquid or gas at its boiling point at atmospheric pressure is called latent heat of vaporization.
Similarly, at a temperature of 373 K (100 °C), steam i.e. the vapor particles have more energy than the water particles at the same temperature, this is because the vapor particles absorb the extra heat in the form of latent heat of vaporization .
Factors Affecting Evaporation:
(1) On increasing the surface area:
(2) Rise in temperature :
(3) Decrease in humidity:
(4) Increase in wind speed :
(1) Increase in surface area: Evaporation being a surface process, the rate of evaporation increases with increase in surface area. This is because adding more surface during evaporation allows the particles of the substance to absorb more and more heat from the surroundings, which increases the kinetic energy of the particles and increases the rate of evaporation.
(2) Rise in temperature: With increase in temperature, particles get more and more kinetic energy due to which vaporization takes place.
(3) Decrease in humidity: The amount of water vapor present in the air is called humidity. The amount of water vapor particles present in the air reduces the thermal energy due to which the rate of evaporation decreases.
(4) Increase in wind speed: Due to the speed of wind, the particles of water vapor fly away rapidly with the wind, due to which the amount of water vapor in the surrounding decreases and evaporation starts easily.
Cooling due to evaporation
During evaporation the liquid keeps on losing its energy and to recover this lost energy, the liquid particles absorb energy from their surroundings and evaporate, due to which the surrounding Coolness comes near Example: Water kept in an earthen pitcher gets cold, feeling cold when perfume, acetone or petrol is dropped on the palm, when perfume, acetone or petrol is dropped on the palm, they start evaporating rapidly. In the process of evaporation, the particles of perfume, acetone or petrol liquid absorb the thermal heat from the palm, due to which the temperature of the palm decreases and coolness is felt on the palm.
Why are water droplets visible on the outer surface of a glass filled with ice water?
The temperature of the outer surface of a glass filled with ice water is very low, due to which the energy of water vapor present in the air, coming in contact with the surface of a glass filled with cold water, is reduced and it turns into a liquid state, which is water vapor. Appears as drops. Hence, water droplets are visible on the outer surface of a glass filled with ice water.
Diffusion: The spontaneous mixing of particles of two different substances is called diffusion.
Diffusion is a process in which particles of matter mix with each other on their own. This is due to the incorporation of particles into the empty spaces. The solid, liquid and gas states of matter are due to the different characteristics of its particles.
Diffusion in Liquids
Diffusion in liquids is possible for solids, liquids and gases. The rate of diffusion is more in liquids than in solids. This is because in the liquid state the particles of matter move freely and there is more free space between the particles of a liquid than in a solid.
Diffusion of gases in liquids: Aquatic organisms use oxygen dissolved in water for respiration.