Chemistry - Energy

1493 Words6 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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(2 marks)
Ignition temperature is the minimum temperature required for the gas or mixture to spontaneously combust.
Activation energy is the minimum amount of energy reactant molecules must possess in order to form products.
The greater the activation energy, the higher is the ignition temperature.

7. Milk kept at room temperature can sour in as little as a day, but can be kept in a refrigerator. Use energy profile and molecular kinetic energy distribution diagrams to explain these observations. (4 marks)
The temperature is the measure of the average kinetic energy of the reacting particles. The increase in temperature also changes the distribution of molecular kinetic energies. Not all reactant particles have the same kinetic energy at the same temperature. At a higher temperature, there are greater proportions of molecules that have kinetic energy more than activation energy.
Therefore, increasing temperature will result in greater number of reactant molecules with kinetic energy greater than the required activation energy, which results in more successful collisions.
The souring of milk is a chemical reaction, so the rate of chemical reaction increases with heat. As the heat increases, the average kinetic energy also increases, meaning that particles collide more often and thus react more often.

8. (6 marks)
a) Explain why the flash point for pentane (- 49°C) is much lower than its ignition temperature
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