NCERT COMPLETE NOTES OF CHEMISTRY CLASS 9th CHAPTER 1 MATTER IN OUR SURROUNDINGS
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MATTER IN OUR SURROUNDINGS
Whenever we look around in our surroundings, we often see various objects be it natural or artificial. When we take a closer note we find that these objects have something in common ie MATTER.
Now, an obvious question that arises in our mind is that
What is Matter?
Anything that occupies space and has mass is called Matter.
I.e. MATTER= VOLUME + MASS
PHYSICAL NATURE OF MATTER
Matter is made up of particles. All the objects that we see in and around us are made up of small particles. For instance, when you break a brick you can small granules of red mud, which can further be broken into smaller parts, called atoms which is the fundamental unit of Matter.
We’ll read more about it in Chapter 3.
CHARACTERISTICS OF PARTICLES OF MATTER
Particles of matter have space between them. This is the reason why particles of one substance get mixed into another. How do we make lemonade? How is it possible to polish our shoes, i.e. where does the polish go when we put it on our shoes?
Interparticle Space is maximum in Gases and least in Solids.
The particles of motion are in constant motion i.e. rotation along with its own axis as well as random motion in any possible direction due to their Kinetic Energy (Energy possessed by particles by the virtue of their motion) and with increase in temperature, the K.E. increases hence, the particles possess more random motion.
This characteristic of motion can be used to explain the phenomenon of DIFFUSION.
The particles of matter intermix on their own, this process of intermixing of particles of two different types is called DIFFUSION.
i) The aroma of food is detected from outside the house. (Diffusion in gas-The particles of food vapour mixes with the air around us, as they possess high speed and occupy the vacant space in air, making the whole air aromatic.)
ii) The vapours of incense stick make the whole room aromatic. (Diffusion in Gas)
iii) It becomes difficult to erase something written on a blackboard when it is left for a while (say one day). (Diffusion in Solid)
iv) Dissolution of ink in water. (Diffusion in liquid)
v) Mixing of CuSO4 crystals in water. (Diffusion of solid in liquid)
Hence, we can say that Diffusion occurs fastest in Gases and slowest in Solids.
3. FORCE OF ATTRACTION
The particles of matter attract each other with some force called the Force of Attraction.
This force varies from matter to matter. The Force of Attraction determines the strength of matter. It’s easier to break a piece of chalk but difficult to break a piece of iron.
The general trend is
STATES OF MATTER
Basically, the states of matter are divided into three broad types i.e. SOLID, LIQUID, and GAS. The differences between the three states are listed as follows:-
CHANGE IN STATE OF MATTER
States of matter are interconvertible. We can change the state of matter by changing the temperature and pressure.
Effect of Change in Temperature
With increase in temperature the kinetic energy of particles starts increasing, the particles start moving at a greater speed, which eventually overcomes the Interparticle Force of Attraction and hence the state changes.
The temperature at which solid melts to become a liquid at the atmospheric pressure is called its Melting Point.
The melting point of a solid indicates the strength of the force of attraction among its particles.
Melting Point of Ice=Freezing point of Water = 0°C = 273K
The temperature at which a liquid starts boiling at the atmospheric pressure is known as its Boiling Point.
Boiling is a bulk phenomenon.
Boiling Point of Water=100°C =373K
SI UNIT OF TEMPERATURE
Kelvin is the SI unit of temperature.
ie. K= °C+273
This is the heat which is present but not seen. ie It cannot be measured by a thermometer. Latent means Hidden. When ice melts to form water at 0°C, rise in temperature isn’t observed even though heat is provided. This heat is used up in changing the state by overcoming the force of attraction among the particles. It is of two types:-
1.Latent heat of Fusion
The amount of heat energy required to change the 1kg of solid into liquid at atmospheric pressure at its melting point is known as Latent Heat of Fusion.
2.Latent Heat of Vaporization
The amount of heat energy required to change the 1kg of liquid into gas at atmospheric pressure at its boiling point is known as Latent Heat of Vaporization.
Latent Heat in case of water can be explained from the following figure-:
· Effect of Change in Pressure
With an increase in pressure, the Interparticle Force of Attraction increases and Interparticle Distance decreases, bringing the particles closer to each other. Hence, the state of matter changes.
The effect of change in temperature and pressure can be summarised as:-
The phenomenon of change of a liquid into vapours at any temperature below its boiling point is called EVAPORATION. It is a Surface Phenomenon.
Factors affecting Evaporation
1. Speed of Wind
2. Surface area
Evaporation increases with an increase in wind speed, surface area and Temperature while it decreases with an increase in Humidity. It is due to Evaporation that
· We prefer to wear cotton clothes in summer. Cotton being a good absorber of water, absorbs sweat from our body, exposes it to the environment, which takes latent heat of Vaporization from our body to convert into Vapour, thereby cooling our bodies.
· We see water droplets on the outer surface of a glass containing water.
· Our palms feel cold when nail polish remover drops on it.
· We sprinkle water on the roof or on the ground after a hot sunny day.
So, students, this was the first chapter of Chemistry. See you soon with exciting new topics of science.