1.0 Introduction to Matter
Everything we see, touch, or feel around us—from the smallest grain of sand to the giant planets in the sky—is made up of Matter. In Physics, we define matter as anything that has mass and occupies space.
What is Matter?
Matter is defined as anything that has mass and occupies volume (space). It is composed of extremely tiny particles called atoms and molecules.
Characteristics of Matter
- Mass: The quantity of matter contained in a body. It is measured in kilograms (kg).
- Volume: The amount of space occupied by an object. It is measured in cubic metres ($m^3$) or litres ($L$).
- Perception: Matter can be perceived by our senses (sight, touch, smell).
Ancient Indian philosopher Maharishi Kanad was the first to propose that matter is made up of very small particles called 'Anu' (atoms) long before modern science confirmed it!
1.1 Composition of Matter
Matter is not continuous; it is particulate in nature. This means it is made of tiny particles which are constantly in motion. These particles are so small that they cannot be seen even with a powerful microscope.
Density Relation
$$Density = \frac{Mass}{Volume}$$
Where: Mass is in $kg$ and Volume is in $m^3$
A wooden block has a mass of 200 kg and occupies a volume of 0.5 $m^3$. Calculate the density of the wood.
Solution:
1. Given: $Mass (m) = 200\,kg$
2. Given: $Volume (V) = 0.5\,m^3$
3. Formula: $Density (D) = \frac{m}{V}$
4. Calculation: $D = \frac{200}{0.5} = 400\,kg/m^3$
Remember, Light, Sound, and Shadows are NOT considered matter because they do not have mass and do not occupy space. They are forms of energy!
2.0 States of Matter
Matter exists in different forms depending on how its constituent particles (atoms or molecules) are arranged. Based on physical properties, matter is primarily classified into three states: Solids, Liquids, and Gases.
The Kinetic Theory of Matter
The state of matter is determined by two main factors:
- Intermolecular Space: The empty space between two molecules.
- Intermolecular Force of Attraction: The force with which molecules pull each other.
1. Solids
In solids, particles are very closely packed. The intermolecular space is negligible, and the force of attraction is very strong.
- Shape & Volume: Definite shape and definite volume.
- Compressibility: Cannot be compressed easily.
- Rigidity: They are hard and rigid.
2. Liquids
In liquids, particles are less closely packed compared to solids. They have more space between them and can move around within the liquid.
- Shape & Volume: No definite shape (take the shape of the container) but have a definite volume.
- Fluidity: They can flow from a higher level to a lower level.
3. Gases
In gases, particles are far apart. The intermolecular space is very large, and the force of attraction is almost zero.
- Shape & Volume: No definite shape and no definite volume.
- Compressibility: Highly compressible.
| Property | Solids | Liquids | Gases |
|---|---|---|---|
| Mass | Definite | Definite | Definite |
| Space | Very Small | Moderate | Very Large |
| Force | Strongest | Weak | Negligible |
Why does a gas fill the entire space of the container it is kept in?
Solution:
In gases, the intermolecular forces of attraction are almost negligible. This allows the particles to move freely in all directions with high speed, thus occupying all the available space in the container.
Students often think that Sponge is not a solid because it can be compressed. However, it is a solid; it compresses only because air is trapped in its pores!
3.0 Change of State of Matter
Matter can change from one physical state to another by changing the temperature or pressure. This process is known as the Inter-conversion of States of Matter. When heat is added or removed, the kinetic energy of the particles changes, leading to a change in state.
Key Processes
- Melting (Fusion): Solid to Liquid (on heating).
- Vaporisation (Boiling): Liquid to Gas (on heating).
- Liquefaction (Condensation): Gas to Liquid (on cooling).
- Freezing (Solidification): Liquid to Solid (on cooling).
- Sublimation: Solid directly to Gas (or vice versa) without passing through the liquid state.
Sublimation: A Special Case
Certain substances like Camphor, Naphthalene balls, and Dry Ice (Solid $CO_2$) do not melt into a liquid. Instead, they jump directly from solid to gas when heated. This process is called Sublimation.
Temperature Conversion
$$K = ^\circ C + 273$$
Where: $K$ = Kelvin (SI Unit), $^\circ C$ = Celsius
The melting point of ice is $0^\circ C$. Express this temperature in the Kelvin scale.
Solution:
1. Given: Temperature in Celsius ($^\circ C$) = $0$
2. Formula: $T(K) = T(^\circ C) + 273$
3. Calculation: $T(K) = 0 + 273 = 273\,K$
Result: The melting point of ice is $273\,K$.
During a change of state, the temperature remains constant even though heat is being supplied. This heat is used to overcome the intermolecular forces and is called Latent Heat.
Dry Ice is actually solid Carbon Dioxide. It is called "dry" because it sublimes directly into gas without leaving any liquid residue behind!
4.0 Evaporation
We often see that water spilled on the floor disappears after some time, or wet clothes dry up under the sun. This happens because of a process called Evaporation. Unlike boiling, evaporation is a slow, silent process that occurs at the surface of a liquid at any temperature below its boiling point.
Factors Affecting Evaporation
The rate of evaporation depends on several physical factors:
- Temperature: Higher temperature increases the kinetic energy of particles, leading to faster evaporation.
- Surface Area: Evaporation is a surface phenomenon. Larger surface area means more particles can escape into the air.
- Humidity: If the air is already full of water vapour (high humidity), evaporation slows down.
- Wind Speed: Moving air carries away water vapour particles, increasing the rate of evaporation.
Evaporation Causes Cooling
When a liquid evaporates, it takes the required latent heat from its surroundings. As a result, the surroundings lose heat and become cool. This is why we feel cool when we sit under a fan after sweating.
Why is water kept in an earthen pot (Matka) cooler than water in a glass bottle?
Solution:
An earthen pot has many microscopic pores on its surface. Water seeps through these pores and evaporates from the outer surface. To evaporate, it absorbs heat from the water inside the pot, making the remaining water cool.
Do not confuse Evaporation with Boiling!
• Evaporation: Occurs at the surface, at all temperatures.
• Boiling: Occurs throughout the liquid (bulk phenomenon), only at a fixed boiling point.
Dogs pant in the summer to cool themselves down. The water on their tongue evaporates, taking away body heat and helping them stay cool!