(Question 2
(a) (i) State Boyle’s law.
- Give the mathematical expression of Boyle’s law.
- Give two reasons why real gases deviate from ideal gas behavior.
- State:
- three postulates of the kinetic theory of gases;
- Dalton’s law of partial pressures
(b) (i) Consider the figure as illustrated below:
Liquid
P Q
Gas Solid
R
State the processes represented by P, Q and R respectively
(ii) Some solids when heated change directly to the gaseous state.
- What name is given to this phenomenon?
- Name two substances which exhibit the phenomenon referred to in 2(b)(ii) I.
(c) If 80 cm3 of methane (CH4) diffuses through a porous membrane in 20 seconds while 50
cm3 of gas Q diffuse through the same membrane in 25 seconds, calculate the molecular mass of gas Q.
[ CH4 = 16.0 ]
- Explain briefly why at room temperature fluorine is a gas while bromine is a liquid.
This question was attempted by majority of the candidates and the performance was fairly good.
In (a), majority of the candidates gave correct statement of Boyle’s law as well as the mathematical expression, but could not give reasons why real gases deviate from ideal gas behaviour.
In (b), processes of freezing, condensation and sublimation were easily identified by majority of the candidates. In (c) some candidates could not solve the problem, however few candidates were able to solve the problem using Graham’s law of diffusion.
In (d) Some candidates could not explain correctly why bromine is a liquid and fluorine a gas at room temperature.