Class 11 Chemistry – Unit 22: Energy (FBISE)
This section provides complete, exam-oriented notes for Class 11 Chemistry Unit 22 – Energy strictly according to the Federal Board (FBISE) syllabus. The unit focuses on understanding different forms of energy and their role in chemical processes and daily life.
Major topics include forms of energy, renewable and non-renewable energy resources, fossil fuels, nuclear energy, solar energy, wind energy, energy crisis, and conservation of energy. The content is explained in a simple and conceptual way with exam-focused points.
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22.1 Origin of Petroleum and Natural Gas
Petroleum, also known as crude oil, was formed over hundreds of millions of years from the remains of marine plants and animals. These remains were buried under layers of sand, rock, and mud. In the absence of air, high heat, pressure, and bacterial activity transformed this organic material into a dark brown, viscous liquid. Natural gas refers to the gas products that accumulate on top of this oil.
22.1.1 Mining and Refining
- Mining: Crude oil is extracted by drilling holes into the earth's crust; natural gas typically emerges first at high pressure, followed by oil extracted via pumps.
- Refining: This is the process of converting crude oil into beneficial products called fractions.
- Fractional Distillation: Crude oil is heated to $400^\circ\text{C}$ in a furnace and passed into a fractionating tower. Vapors rise and condense at different levels based on their boiling points.
- Condensation Pattern: Compounds with the highest boiling points condense first near the bottom, while those with the lowest boiling points condense last near the top.
Table 22.1: Fractions of Petroleum and Their Uses
| Fraction | Carbon Atoms | Boiling Point ($^\circ\text{C}$) | Important Uses |
|---|---|---|---|
| Liquefied petroleum gas (LPG) | 1-4 | Below 20 | Cylinder gas for cooking |
| Petrol | 5-10 | 35-70 | Fuel for motor cars and vehicles |
| Naphtha | 8-12 | 70-120 | Chemical feedstock for drugs, plastics, and chemicals |
| Kerosene | 10-16 | 170-250 | Fuel for jet planes, heating, lighting, and cooking |
| Diesel | 14-20 | 270-340 | Fuel for buses, trucks, and trains |
| Lubricating oil | 20-50 | 350-500 | Lubricants for engines, waxes, and polishes |
| Fuel oil | 50-70 | 500-600 | Fuel for power stations, factories, and ships |
| Bitumen | More than 70 | More than 500 | Paving roads and making roofing materials |
Questions & Answers
Q1: What physical property is used to separate crude oil into different fractions?A: Crude oil is separated based on the boiling points of its constituent hydrocarbons.
Q2: Which fraction is used as a feedstock for the pharmaceutical and plastics industries?A: Naphtha is used as the chemical feedstock for making drugs, plastics, and other chemicals.
Q3: Why do some compounds collect at the very bottom of the fractionating tower as residue?A: Compounds that do not boil at the furnace temperature (such as Bitumen) collect at the bottom as residue. These compounds have very high boiling points, typically exceeding $500^\circ\text{C}$.
Q4: Describe the relationship between the number of carbon atoms and the boiling point in petroleum fractions.A: There is a direct relationship: as the number of carbon atoms per molecule increases, the boiling point also increases. For example, LPG (1-4 carbons) boils below $20^\circ\text{C}$, while Bitumen (70+ carbons) boils above $500^\circ\text{C}$.