(i) State Two assumptions of the kinetic theory of gases
(ii) When some solids are heated, they change directly into the gaseous state. What narne is given to this phenomenon?
(iii) List two substances which exhibit the phenomenon referred to in (a)(ii) above
(iv) Write an expression to show the mathematical relationship between the rate of diffusion of a gas and its vapour density.
(b) Consider the following equilibrium reaction:
3Fe\(_{(s)}\) + 4H\(_2\)O\(_{(g)}\) \(\rightleftharpoons\) FeO\(_3\)O\(_{4(s)}\) + 4H\(_{2(g)}\), \(\Delta\)H = – 150KJ mol\(^{-1}\)
Explain the effect of the following factors on the position of equilibrium: (i) tecrease in temperature; (ii) Increase in pressure; (iii) Removal of hydrogen.
(c) . Three beakers labelled P, Q and S each contained zinc metal of the same mass but in different forms. P contained a length of zinc rod, Q contained zinc dust while S contained zinc foil. 100cm\(^3\) of 5.0 mol dm\(^{-3}\) hydrochloric acid was added to each beaker to react with all the zinc.
(i) State the order in which the reaction came to completion in beakers P,Q and S starting with the fastest.
(ii) Give reason for your answer in (c)(i) above
(iii) Write an equation to represent the reaction between zinc rid the hydrochloric acid.
(d) (i) What is meant by pH of a solution?
(ii)(I) State with reason in each case whether the pH would increase, decrease or remain constant if the following experiments were carried out Neutralizing bench HNO\(_3\);
II. Diluting 25.0 cm\(^3\) of a given NaOH solution to 100.0cm\(^3\) Concentrating a solution of NaCI.
Explanation
The assumptions of kinetic theory of gases are:
-The forces of attraction between gas particles are legligible
-Gas molecules move randomly in straight lines
-They collide with one another and with the walls of the container
-The collision of the molecules is perfectly elastic.
(ii) Sublimation
(iii) Ammonium chloride (NH\(_4\)CI), iodine (I\(_2\), naphthalene and aluminium chloride.
(iv) \(\Delta\) = \(\frac{1}{\sqrt{d}}\) or r = \(\frac{k}{\sqrt{d}}\)
(b) 3Fe\(_{(s)}\) + 4H\(_2\)O \(\rightleftharpoons\) Fe\(_3\)O\(_{4(s)}\) + 4H\(_{2(g)}\); \(\Delta\)H = -150KJ mol\(^{-1}\)
(i) The forward reaction is exothermic, decrease in temperature will favour the forward reaction or the position of equilibrium shifts to the right.
(ii) There will be no effect on the position. of equilibrium as the number of gaseous molecules are the same on both sides.
(iii) Removal of hydrogen Shifts the position of equilibrium to the right because of the decrease in concentration of H\(_2\). hence more Fe\(_{(s)}\) and water will react to produce more H\(_2\).
(c)(i) Q > S > P.
(ii) The larger the surface area of a solid reactant, the faster the-reaction rate. The surface area of zinc dust is the largest while that of the rod is the smallest.
(iii) Zn\(_{(s)}\) + 2HCl\(_{(aq)}\) \(\to\) ZnCl\(_{2(aq)}\) + H\(_{2(g)}\)
(d)(i) The pH of a solution is a measure of the degree of acidity or alkalinity of the solution.
(ii) (-) The pH increases because acidity decreases
(-) pH decreases because alkalinity decreases
(-) pH remains constant because the salt solution is neutral
(II) Non-catalysed activated complex (I).
(ii) Activation energy (I) with catalyst
(iii) Enthaipy change (\(\Delta\)H)