Question 9
- (i) State Boyle’s law
(ii) State two assumptions of the kinetic theory of gas necessary for a real gas to be considered as ideal.
- (i) Explain the term renewal energy.
(ii) List four examples of renewable energy.
- Why is the maximum arm of the Six’s maximum and minimum thermometer not completely filled with alcohol whereas the minimum arm is filled
- A electric heater rated 100 W is used to raise the temperature of 200 g of water in a flask from 30oC to 100oC. The water is boiled for further 2 minutes before the heater is switched off. Neglecting heat losses, calculate the:
- Quantity of energy supplied to the water in raising its temperature to 100oC.
(ii) mass of steam that escaped.
[Specific heat capacity of water = 4.2 x 103 J kg-1 K-1; specific latent heat of vaporization of steam = 3.3 x 106 J kg-1]
Observation
Part (a) (i) Majority of the candidates stated the law correctly. Candidates’ performance was above average.
(ii) Many candidates could not state the assumptions of kinetic theory of gases. Classroom teachers should endeavor to give more attention to this topic.
Part (b) (i) A very high percentage of the candidates got the whole mark mentioning the sources of renewable energy but struggled with the explanation. Performance was low.
(ii) Most candidates were able to state the examples of renewable energy. Performance was above average.
Part (c): Most candidates avoided this question. Performance was very poor.
Part (d) (i): Candidates performance was above average
(ii) Very few candidates were able to correctly solve the problem. Candidates’ performance was below average
The expected answer is:
9. (a) (i) Boyle’s Law
The pressure of a fixed/given mass of gas at constant temperature is inversely proportional to the volume of the gas.
(ii) Assumptions of the Kinetic Theory of Gases
- (forces) of attraction among/between the molecules are negligible;
- the volume of the molecules is negligible compared with the
volume occupied by the gas;
(b)(i) Renewable Energy
Energy that is continuously replenished by natural resources
(ii) Examples of Renewable Energy
Energy from
- ocean/water;
- dams;
- wind;
- sun;
- biomass.
(c)(i) Six’s Thermometer
During the day, rise in atmospheric temperature causes the alcohol in the maximum arm to expand. The space accommodates this expansion to prevent cracking of the glass. At night, no expansion takes place in the minimum arm
