Chapter 1 - Chemistry
Anything that occupies space and has mass and is felt by senses is known as matter.
They are classified on the basis of:
Matter is classified into:
| Properties | Solid | Liquid | Gas |
|---|---|---|---|
| Shape and Size | Has definite shape | No fixed definite shape, takes the shape of the container | Has indefinite shape, molecules are due to loose arrangement/random motion |
| Volume | Fixed volume | Fixed volume | No fixed volume |
| Intermolecular Distance | Least intermolecular distance | Less intermolecular distance than gases and more than solids | Maximum intermolecular distance between particles |
| Intermolecular Force of Attraction | Maximum force of attraction between molecules | Less intermolecular force of attraction compared to solid | Minimum intermolecular force of attraction between particle molecules |
| Compressibility | No compressibility (cannot be compressed easily) | Slight compressibility (can be compressed to small extent) | High compressibility (can be compressed easily) |
| Diffusion | Can diffuse into liquid | Diffusion is slightly higher than solids | Diffusion is highest as particles move randomly at high speed |
| Density | Highest | Low | Very low |
| Kinetic Energy | Very low | Intermediate | Highest |
Solid → heat → Liquid → heat → Gas → Cool
Example: Ice is heated it changes into water. If water is heated it changes into steam. If steam is cooled it changes into water and if water is cooled it changes into ice.
When a solid is heated the particles begin to vibrate with greater speed and begin to move more freely. Then at a particular temperature the solid melts and changes into liquid. This process of melting is known as fusion.
The temperature at which solid melts is known as melting point. The melting point of ice is 0°C (273.15 K).
The amount of heat energy required to change 1 kg of solid into liquid at atmospheric pressure at its melting point is called latent heat of fusion.
\[ Q = mL \]
where:
\( Q \) = latent heat of fusion
\( m \) = mass of substance
\( L \) = specific latent heat of solid
When a liquid is heated its particles begin to move even faster. Then at a particular temperature the liquid begins to boil and changes into gas (vapour).
The temperature at which the liquid starts boiling is known as boiling point. The boiling point of water is 100°C (373.15 K).
The amount of heat energy required to change 1 kg of liquid into vapour at atmospheric pressure at its boiling point is called latent heat of vaporisation.
Interchange of Matter: For example, water exists as solid in the form of ice, as liquid in the form of water, and as gas in the form of vapour.
A substance transforms from a solid to a gas by heating without ever going through a liquid phase; this process is known as sublimation.
The heat energy which is required to convert solid into vapour state is known as sublimation energy.
Examples: Ammonium chloride, iodine, naphthalene balls, dry ice, camphor.
The temperature at which any solid substance changes into liquid substance is known as melting point. At the melting point there are two states of matter (Solid, Liquid) that exist simultaneously.
Example: Melting point and freezing point of water is 0°C.
\[ Q = m \cdot s \cdot \Delta T \]
where:
\( \Delta T \) = temperature difference
\( s \) = specific heat
The process by which any solid substance changes into liquid substance is known as fusion.
The temperature at which the liquid state of matter changes into solid state at that temperature is known as freezing point.
Example: Freezing point of water is 0°C.
\[ T(K) = T(°C) + 273.16 \]
The process in which any liquid substance changes into vapour state at any temperature below its boiling point, at atmospheric pressure is called evaporation.
Note: The rate of evaporation increases on increasing temperature, surface area and wind speed, and rate of evaporation decreases on increasing humidity.
| Vaporisation | Evaporation |
|---|---|
| Process by which liquid changes into vapour state at its boiling point | Process by which liquid changes into vapour at any temperature below its boiling point |
| It is a bulk phenomenon | It is a surface phenomenon |
| It is a fast and violent process | It is slow and silent process |
| Temperature during vaporisation does not change | Temperature changes during evaporation |
Condensation is the process through which the physical state of matter changes from the gaseous phase into the liquid phase.
Example: Condensation occurs when water vapor in the air changes into liquid (water) when it comes in contact with a cooler surface.