CHAPTER-1 MATTER IN OUR SURROUNDINGS
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| matter in our surroundings |
Everything we see around us in the universe is made up of matter. The matter is something which has mass and needs space to occupy. You have studies about the classification of matter in our surroundings in lower grades as solid, liquid and gas.
Scientists have made two types of classification of matter based on its physical properties and chemical nature.
PHYSICAL NATURE OF MATTER
(a) Matter is made up of particles
When we dissolve salt in water, the level of water level remains the same. This is due to the small particle size of salt, which occupies the space between the water molecules. Particles of salt and water mix up together to make the salt solution.
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PARTICLES IN MATTER
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(b) Particles of matter are very small
When few crystals of copper sulphate are dissolved in water, it forms a blue coloured solution. On diluting this solution to three or more times, still, we can observe the blue colour. This indicates the presence of small particles of copper sulphate in the solution even after dilution.
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| COPPER SULPHATE SOLUTION |
CHARACTERISTICS OF PARTICLES OF MATTER
- Particles of matter have space between them.
- Particles of matter are continuously moving.
- Particles of matter attract each other.
Activity-1
Take some crystals of potassium permanganate and add it to water taken in a beaker. Check the change in water level before and after addition.
We can observe that there is no change in water level. This indicates that there is enough space between the particles of water and potassium permanganate crystals have occupied those space.
We can conclude that there is a space between the particles of matter.
Activity-2
Drop a few crystals of copper sulphate into a beaker containing hot water and another one containing cold water. Keep it aside for some time without disturbing.
We can observe that particles of copper sulphate in hot water got mixed up faster than cold water. The rate of mixing increases with increase in temperature.
We can conclude that particles of matter are continuously moving and possess kinetic energy. With the increase in temperature, the kinetic energy of the particles also increases.
DIFFUSION- The process of intermixing of particles by its own is called diffusion.The rate of diffusion increases with increase in temperature.
Rate of diffusion is as follows:
gas ＞ liquid＞solid
Activity-3
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| RUNNING WATER |
When you are trying to break the stream of water of running tap water with your finger, we can easily do it. But if we are trying to cut through a wall, it is not possible.
This proves that the particles of matter in the liquid state have less force of attraction than solid-state.
Rate of attraction is as follows:
solid state＞liquid state＞gaseous state
DIFFERENCE BETWEEN SOLID, LIQUID AND GAS
| SOLID | LIQUID | GAS |
| definite shape | no definite shape | no definite shape |
| definite volume | definite volume | no definite volume |
| do not flow | can flow | can flow |
| minimum intermolecular space | more intermolecular space
than solid | maximum intermolecular space |
the maximum force of attraction
between particles | less force of attraction than
solid | a minimum force of attraction |
| negligible compressibility | more compressible than solid | highly compressible |
Two examples of gases which are used widely after compression-LPG (liquified petroleum gas) and CNG (compressed natural gas)
The pressure of gas- The gas particles in a container are continuously moving. During this random movement, they hit each other and also collide with the walls of the container.
The pressure of a gas is due to the force exerted by the particles of gas per unit area on the wall of the container.
EFFECT OF CHANGE OF TEMPERATURE ON MATTER
The kinetic energy of the particles increases by increasing the temperature of solids. The particles start vibrating and overcome the force of attraction and change into liquid form.
The temperature at which the solid melts and forms into a liquid at the atmospheric pressure are called the melting point.
The melting point of ice is 273.16 K or 0⁰C.
The process of melting is also called fusion.
Latent heat of fusion- During melting of ice, we can observe that the temperature of the system does not rise until all ice melts. The heat supplied is used to overcome the force of attraction and it will be in the form of hidden energy. This hidden energy is called latent heat.
The amount of heat energy required to change 1 kg of a solid into liquid at its melting point at the atmospheric pressure is called the latent heat of fusion.
So when you compare the particles of water and ice at 273 K, water has more energy than ice.
Similarly, we can explain the latent heat of vapourisation in the case of boiling of water to steam.
The temperature at which the liquid changes to gaseous form at the atmospheric pressure is called the boiling point.
Boiling is a bulk phenomenon, but evaporation is a surface phenomenon. The boiling point of water is 373 K or 100⁰C.
Particles in steam have more energy than particles in water at 373 K because particles in vapour state have absorbed extra energy in the form of latent heat of vaporisation. Hence steam burning is more severe than water at the same temperature.
To convert Celcius to Kelvin, add 273 and to convert Kelvin scale to Celcius, subtract 273.
5⁰C= 5+273=278 K
Sublimation- The process of change of state directly from solid to a gas without changing into a liquid state is called sublimation.
Example for sublimable substances- ammonium chloride, naphthalene(mothballs), anthracene, dry ice
EFFECT OF CHANGE OF PRESSURE
On applying pressure and compressing gas, the particles will come closer and change its state into liquid. The conditions for liquifying a gas are -
- By increasing pressure
- By reducing temperature.
DRY ICE- solid carbon dioxide is called dry ice. It is stored under high pressure and when it is exposed to air, it gets converted to the gaseous form without going to its liquid state.
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| DRY ICE IN A JAR |
EVAPORATION AND THE FACTORS AFFECTING EVAPORATION
Liquids can change into its vapour state at any temperature below at its boiling point. This phenomenon is called evaporation.
In liquids, the particles at the surface are having more kinetic energy than in the bulk and are able to overcome the force of attraction easily and changes into the vapour state.
Factors affecting evaporation are:
- increase in temperature
- increase in wind speed
- increase in surface area
- decrease in humidity
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| DRYING CLOTHES |
When temperature increases, more particles will get kinetic energy to get converted into vapour state and the rate of evaporation increases.
When the surface area is increased, more area of exposure increases and the rate of evaporation is increased.
Humidity is the amount of water vapour in the air. If the air is more humid, it can not hold more water vapour which is coming through evaporation.
So the evaporation rate is decreased when humidity is more. That is why clothes are drying up slowly on a cloudy rainy day.
Evaporation can cause a cooling effect-
The particles of liquid can absorb more heat energy from the surroundings in order to regain the energy lost during the evaporation process. This makes the surrounding cool.
Example: nail polish remover will take heat from our body and we feel cool. For evaporation of sweat, it takes heat energy from our body and we feel cool.
In our daily life, we can relate the topic of evaporation to many instances.
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