Introduction
Everything in this universe is made up of material which scientists have named “matter”.
The air we breathe, the food we eat, stones, clouds, stars, plants and animals, even a small drop of water or a particle of sand – every thing is matter. Matter is defined as having both mass and volume.
Modern day scientists have evolved two types of classification of matter based on their physical properties and chemical nature.
Some people believed matter to be continuous while others thought of it to be made up of particulate matter.
Characteristics of Particles of Matter
Particles of matter have space between them. There is enough space between particles to dissolve other particles.
Particles of matter are continuously moving; they possess what we call the kinetic energy.
As the temperature rises, particles move faster. So, we can say that with increase in temperature the kinetic energy of the particles also increases.
This intermixing of particles of two different types of matter on their own is called diffusion. We also observe that on heating, diffusion becomes faster.
Particles of matter attract each other. Particles of matter have force acting between them. This force keeps the particles together. The strength of this force of attraction varies from one kind of matter to another.
States Of Matter
Matter exists in 3 states around us :
Solids
Liquids
Gases
These states of matter arise due to the variation in the characteristics of the particles of matter.
Solids | Liquids | Gases |
-Have a definite shape, distinct boundaries and fixed volumes. | -No fixed shape but have a fixed volume. | -No fixed shape or volume |
-Negligible compressibility tendency to maintain their shape when subjected to outside force. | -Liquids flow and change shape | -Gases are highly compressible as compared to solids and liquids. |
-They are rigid | -They are not rigid but can be called fluid. | - Can be compressed and stored in cylinders such as CNG and LPG. |
- Rubber changes shape on external force but regains its shape. -Sponge can be compressed because it has air trapped inside | - The aquatic animals can breathe under water due to the presence of dissolved oxygen in water. Thus, we may conclude that solids, liquids and gases can diffuse into liquids. | - The smell of food reaching your nostrils is due to high rate of diffusion. |
- Rate of diffusion is slow | - Rate of diffusion is faster than solids because they have more space between them. | - Rate of diffusion is highest |
Can Matter Change its State? - YES!!
Melting of Solids ( Solids to Liquids)
• On increasing the temperature of solids, the kinetic energy of the particles increases.
• Particles start vibrating with faster speed and their energy can now overcome the force of attraction between them.
• The particles leave their fixed positions and start moving more freely.
• A stage is reached when the solid melts and is converted to a liquid. The minimum temperature at which a solid melts to become a liquid at the atmospheric pressure is called its melting point.
• The temperature at which a liquid starts boiling at the atmospheric pressure is known as its boiling point.
HIGHER THE MELTING/BOILING POINT HIGHER THE FORCE OF ATTRACTION BETWEEN PARTICLES
The melting point of ice is 273.15 K*. The process of melting, that is, change of solid state into liquid state is also known as fusion.
When a solid melts its temperature remains the same while it is melting. So where does this heat energy go?
This heat gets used up in changing the state by overcoming the forces of attraction between the particles. This heat required to change 1Kg of solid to liquid at atmospheric pressure at its melting point without changing its temperature is called the latent heat of fusion. The word latent means hidden.
So, particles in water at 00 C (273 K) have more energy as compared to particles in ice at the same temperature.
Latent heat of vaporization? -
Sublime Solids:
There are substances which change directly from Solids to Gases; and directly from Gases to Solids
A change of state directly from solid to gas without changing into liquid state is called sublimation and the direct change of gas to solid without changing into liquid is called deposition.
Effect of Change of Pressure
What will happen when we start putting pressure and compress a gas enclosed in a cylinder? Will the particles come closer? Do you think that increasing or decreasing the pressure can change the state of matter?
Applying pressure and reducing temperature can liquefy gases (Recall LPG and CNG)
Solid Carbon Dioxide (CO2) is stored under high pressure. Solid CO2 gets converted directly to gaseous state on decrease of pressure to 1 atmosphere without coming into liquid state. This is the reason that solid carbon dioxide is also known as dry ice.
Pressure and temperature determine the state of a substance, whether it will be solid, liquid or gas.
Can state be changed without reaching melting or boiling point? - Yes!!
- In the case of liquids, a small fraction of particles at the surface, having higher kinetic energy, is able to break away from the forces of attraction of other particles and gets converted into vapor. This phenomenon of change of a liquid into vapors at any temperature below its boiling point is called evaporation.
Factors affecting vaporization
- Increased Surface Area
- Increase in Temperature
- Decrease in Humidity
- Increase in Wind Speed
How Does Evaporation Cause Cooling?
The particles of liquid absorb energy from the surrounding to regain the energy lost during evaporation.
This absorption of energy from the surroundings make the surroundings cold.
When you pour acetone (Nail polish Remover/Spirit) on your body it feels cold because the particles absorb heat from our skin.
People sprinkle water on roof on hot days because the latent heat of vaporization will help in cooling the hot roof.
We wear cotton in summers as it is a good absorber of water helps in absorbing the sweat and exposing it to the atmosphere for easy evaporation.
