FUELS

What is a fuel?

• Fuel is a substance which can provide useful energy.

•A fuel normally uses oxygen gas in the air and produce energy (heat)•See the above fire triangle

Hydrocarbons

• Hydrocarbons are those compounds made up of carbon and hydrogen only.

• Gas, petrol, diesel and oil are hydrocarbons and they are fuels

• Hydrocarbons on burning produce carbon dioxide and water together with heat energy.

• The energy comes out is used for various purposes.

Surface area

• When a solid changed in to powder form, the surface area increases

• Large surface area can make a reaction dangerously fast.

• Flour dust has a large surface area.• It burns very fast.• So a spark from a machine, or a lit match, can

cause explosion.

• In wood mills, and factories making things like custard powder, instant coffee, sugar and dried milk have high risk of explosion.

• Oxygen in the air is also used for gas welding.

• In gas welding, acetylene (ethyne) gas is mixed with oxygen; the flame is very hot

• Oxygen cylinders are used in hospitals and by deep sea swimmers for artificial breathing..

• Methane is a gas produced from decaying organic materials. It comes from the intestine of cattle. Also from marshy places.

• Methane is used as a fuel

Different fuels• Fuels can be solid, liquid or gas• Solid fuel: Coal, charcoal, firewood• Liquid fuel: Petrol, Diesel, Oil, Alcohol• Gas fuel: Natural gas, Butane, Hydrogen

• Can you name some more fuels and their uses?

Exothermic and endothermic reactions

• Heat is given out in an exothermic reaction.• So surrounding gets hot during exothermic

reactions.• Heat is taken in during endothermic reaction.• So a cooling effect takes place in endothermic

reactions.• Burning of fuel, respiration etc are exothermic• Dissolving ammonium chloride in water,

Evaporation, photosynthesis etc are endothermic

Pollution

• Pollution is a process of making our environment poisonous.

• Combustion (of fuel) makes air pollution.• Can be from motor vehicles, factories etc.,• Lead compounds and carbon monoxide are air

pollutants. • These are normally produced when petrol is

burnt in motor engines.

• Unleaded petrol is available these days.• Carbon monoxide combines with haemoglobin in

blood. • Thus blood will stop carrying oxygen to various

parts of the body.• Oxides of sulphur (sulphur dioxide) and Nitrogen

(nitrogen oxide) are acidic oxides.• They mix with rain water to form acid rains. • Acid rains kill plants and make soil acidic.

• How to remove soil acidity?• Acid rains also weaken building (especially those

buildings made up of lime stone)

Batteries

Reactivity series

• Metals arranged according to their reactivity with oxygen, water, acid etc is called a reactivity series.

• Metals at the top of the series are more reactive and the reactivity decreases down the series.

How do metals react?• Metals lose electrons in a reaction• Electrons are negative.• So by losing electrons, metal atoms become

positive ions.• Reactivity of a metal depends on how fast the

metal atom can lose electron and becomes positive ions (cations)

Cell

• A cell consists of a two electrodes (one positive and one negative) placed in an electrolyte.

Voltage

• Voltage of a cell depends on the two electrode metals.

• If the difference in the reactivity of the two metals is very high, voltage produced is also very high.

• Reactivity difference can be determined by looking at the reactivity series

• The electrodes in a cell are magnesium and copper and another cell with Lead and copper.

• The reactivity difference in the first cell is high.

• So the voltage from the first cell is larger.

• In a cell, electricity is generated due to chemical reaction between metal electrodes with the electrolyte.

• When the reagents finished (electrode or electrolyte), cell is called ‘dead’.

• Different batteries are used for different purposes

• A battery is a series of cells.• Cells of a car battery are different from the

cells used in a remote control.• When cells are made, they must be easier to

use and cost effective.

Different types of cells

• Simple cells• A Simple cell is a device that converts chemical

energy into electrical energy.• Rechargeable battery is made up of many simple

cells. By providing charges, the chemical reactions are electrically reversed.

• Fuel cell• A fuel cell is an electrochemical cell that converts

energy from a fuel into electrical energy.

Different types of cells

Simple cell Rechargeable cells Fuel cell

Rusting• Iron reacts with oxygen in the air and joins

with water is called rusting.• Rust is chemically hydrated iron oxide.• Rusting is a kind of corrosion of metal iron.• Two necessary conditions for rusting are:• Oxygen and water.• Oiling, painting, greasing, make a coating of

plastic, making stainless steel and anodising are different methods to prevent rusting.

Rusting experiment

THE END