Essay on Chemistry - Energy

1486 Words Oct 3rd, 2008 6 Pages
1. “The energy for life comes from the sun.”
Outline the role of the photosynthesis process to explain what is meant by this statement. (3 marks) chlorophyll
6CO2(g) + 6H2O(l) + energy C6 H12 O6 (aq) + 6O2(g) 2830 kJ glucose

Photosynthesis is the process in which plants use the sun’s light energy to convert carbon dioxide and water into carbohydrates such as glucose, sucrose, starch and cellulose.
Carbohydrates are high energy compounds because when they react with oxygen, they produce large amounts of energy. Plants make their own food by using the glucose they produces as an energy source for growth, reproduction, repairing damaged tissues... Animals cannot carry out
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Spontaneous combustion occurs when a substance doesn’t require the application of external energy in order to combust. It occurs when small particles of coal or gaseous fuel are sprayed into excess air. For example: the exposure of white phosphorus forms an oxide because the heat from this reaction is enough to ignite the rest of the phosphorus.
Explosive combustion is an uncontrolled chemical reaction that occurs at a very fast rate in which heat is released. Explosions occur when there are high concentrations of gases or finely divided solid particles of materials (as the surface area is increased) in excess heated air. For example: cylinders of petrol and diesel engines in vehicles.

5. Describe the role of catalysts in chemical reactions, using a named industrial catalyst as an example. (2 marks)
A catalyst is a substance which increases the rate of chemical reaction by providing an alternative pathway with lower activation energy without itself being consumed or permanently changed.
Palladium or nickel catalyst is used in the margarine industry in the process of hydrogenation of unsaturated fats to saturated fats. Hydrogen molecules and unsaturated hydrocarbon molecules are absorbed onto the surface of the catalyst and the bonds between the hydrogen atoms break as new metal-hydrocarbon molecules form. The absorbed atoms migrate to the metal surface

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