Introduction
Matter exists in different physical forms called states or phases. The most commonly known states are solid, liquid, and gas, with plasma and Bose-Einstein condensate (BEC) being two additional states observed under extreme conditions. In everyday life and chemical processes, we most often deal with the first three. The interconversion of states of matter refers to the transformation of matter from one state to another by changing temperature or pressure.
Understanding these transformations is fundamental in chemistry, physics, and even industrial applications like refrigeration, distillation, and metallurgy.
States of Matter: A Quick Overview
1. Solid
- Particles are tightly packed in a regular arrangement.
- They vibrate but do not move from their positions.
- Definite shape and volume.
- Example: Ice, iron, wood.
2. Liquid
- Particles are loosely packed with more freedom to move.
- No definite shape but has a definite volume.
- Example: Water, oil, alcohol.
3. Gas
- Particles are far apart and move freely.
- No definite shape or volume.
- Compressible and expandable.
- Example: Oxygen, nitrogen, carbon dioxide.
Processes of Interconversion
There are six major processes of interconversion of matter:
| From | To | Process |
|---|---|---|
| Solid | Liquid | Melting (Fusion) |
| Liquid | Solid | Freezing (Solidification) |
| Liquid | Gas | Vaporization (Boiling or Evaporation) |
| Gas | Liquid | Condensation |
| Solid | Gas | Sublimation |
| Gas | Solid | Deposition |
Let’s now explore each process in detail with examples.
1. Melting (Fusion)
Definition: Melting is the process of changing a substance from a solid to a liquid by heating it to its melting point.
Explanation:
When a solid is heated, its particles gain energy and start vibrating more vigorously. At a certain temperature, the energy becomes sufficient to overcome the forces holding the particles together, and the solid turns into a liquid.
Example:
Ice melts into water at 0°C. This is a physical change and is reversible.
Equation:
Ice (solid) → Water (liquid) at 0°C
2. Freezing (Solidification)
Definition: Freezing is the process of changing a liquid into a solid by cooling it to its freezing point.
Explanation:
As the liquid cools, its particles lose kinetic energy and move slower. When the temperature drops to the freezing point, the particles lock into fixed positions, forming a solid.
Example:
Water freezes into ice at 0°C.
Equation:
Water (liquid) → Ice (solid) at 0°C
3. Vaporization (Boiling or Evaporation)
Definition: Vaporization is the process of converting a liquid into a gas.
Boiling vs Evaporation:
- Boiling occurs throughout the liquid at its boiling point (e.g., water at 100°C).
- Evaporation happens at the surface of the liquid at any temperature below boiling point.
Example:
Water boils to form steam at 100°C.
Equation:
Water (liquid) → Steam (gas) at 100°C
4. Condensation
Definition: Condensation is the process of changing a gas into a liquid by cooling.
Explanation:
When a gas is cooled, its particles lose energy and come closer together. At a certain temperature, the gas particles form a liquid.
Example:
Steam condenses into water when it cools down.
Equation:
Steam (gas) → Water (liquid)
5. Sublimation
Definition: Sublimation is the direct conversion of a solid into a gas without passing through the liquid state.
Explanation:
Some substances have strong intermolecular forces that allow them to jump directly to the gaseous state when heated.
Example:
- Camphor and naphthalene balls sublimate.
- Dry ice (solid CO₂) sublimates into gas at room temperature.
Equation:
Camphor (solid) → Camphor vapour (gas)
6. Deposition
Definition: Deposition is the reverse of sublimation, where a gas changes directly into a solid without becoming a liquid.
Example:
Frost formation from water vapor on cold surfaces.
Equation:
Water vapour (gas) → Ice (solid)
Factors Affecting Interconversion
1. Temperature
- Raising temperature increases kinetic energy of particles, leading to melting or vaporization.
- Lowering temperature causes freezing or condensation.
2. Pressure
- Increasing pressure can turn gas into liquid (e.g., liquefied petroleum gas).
- Decreasing pressure can aid sublimation (e.g., freeze-drying in food preservation).
Real-Life Applications
1. Cooking
- Water boiling to cook food (liquid to gas).
- Butter melting in a pan (solid to liquid).
2. Refrigeration
- Coolants like Freon undergo evaporation and condensation cycles.
3. Industrial
- Sublimation used in the purification of camphor.
- Liquefaction of gases for storage and transport (oxygen, LPG).
4. Meteorology
- Cloud formation (condensation).
- Snow and frost (deposition).
- Hailstones form by freezing.
Energy Changes During Interconversion
Endothermic Processes (heat is absorbed):
- Melting
- Boiling
- Sublimation
Exothermic Processes (heat is released):
- Freezing
- Condensation
- Deposition
Graphical Representation: Heating Curve
When a solid is heated:
- Temperature rises until melting point.
- Flat line during melting – energy used to break bonds.
- Temperature rises again until boiling point.
- Flat line during boiling – energy used to overcome attractions between molecules.
This graph is called a heating curve and shows temperature vs time.
Conclusion
The interconversion of states of matter is a fundamental concept in chemistry, crucial for understanding both natural phenomena and industrial processes. By changing temperature and pressure, we can manipulate the state of a substance to suit various applications. These changes are physical, reversible, and involve energy exchange in the form of heat. Whether it’s melting ice, boiling water, or sublimating dry ice, the transformations remind us of the dynamic nature of matter and its response to environmental conditions.
Question
Earthen pitches are more effective in Hyderabad than in Chennai. Justify.
Answer
The rate of evaporation of water depends on humidity(moisture present in atmosphere).The more the humidity, the less is the rate of evaporation. In coastal areas like Chennai, moisture is more, and hence ,the rate of evaporation of water is less. In case of non-coastal areas like Hyderabad, moisture is less, and hence, the rate the rate of evaporation is more. Hence, a higher rate of evaporation allows faster cooling of water in the earthen pitcher in Hyderabad when compared to Chennai.
People are advised to wear cotton clothes in summer. Give reason.
Ans
Cotton has the property of absorbing sweat. When this is exposed to atmosphere, sweat undergoes evaporation which causes cooling, and hence we feel cool by wearing cotton clothes in summer.
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