(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.
(a)(i) Two assumptions of the kinetic theory of gases: gas molecules are in constant, rapid, random motion; the actual volume of the molecules is negligible compared with the volume of the container (and there are negligible forces between molecules).
(ii) The phenomenon is sublimation.
(iii) Substances that sublime: iodine and ammonium chloride (also solid CO2, naphthalene, camphor).
(iv) Rate of diffusion is inversely proportional to the square root of the vapour density:
\[R \propto \frac{1}{\sqrt{d}}\]
(b) For \(3Fe_{(s)} + 4H_2O_{(g)} \rightleftharpoons Fe_3O_4_{(s)} + 4H_{2(g)}\), \(\Delta H = -150\ \text{kJ mol}^{-1}\) (exothermic):
- (i) Decrease in temperature: favours the exothermic forward reaction, so the equilibrium shifts to the right (more hydrogen).
- (ii) Increase in pressure: there are 4 moles of gas on each side, so pressure has no effect on the position of equilibrium.
- (iii) Removal of hydrogen: the equilibrium shifts to the right to replace the hydrogen removed.
(c)(i) Order (fastest first): Q (dust) > S (foil) > P (rod).
(ii) The rate depends on surface area. Zinc dust has the largest surface area exposed to the acid (fastest), the foil an intermediate area, and the rod the smallest surface area (slowest).
(iii) \[Zn + 2HCl \rightarrow ZnCl_2 + H_2\]
(d)(i) The pH of a solution is the negative logarithm to base ten of the hydrogen ion concentration, \(pH = -\log[H^+]\).
(ii)
- I. Neutralizing bench HNO3 with a base: the pH increases as H+ ions are removed.
- II. Diluting 25.0 cm3 of NaOH to 100.0 cm3: the pH decreases as the alkali becomes more dilute (lower [OH-]).
- III. Concentrating a solution of NaCl: the pH remains constant, because NaCl is a neutral salt and does not change [H+].
(a)(i) Two assumptions of the kinetic theory of gases: gas molecules are in constant, rapid, random motion; the actual volume of the molecules is negligible compared with the volume of the container (and there are negligible forces between molecules).
(ii) The phenomenon is sublimation.
(iii) Substances that sublime: iodine and ammonium chloride (also solid CO2, naphthalene, camphor).
(iv) Rate of diffusion is inversely proportional to the square root of the vapour density:
\[R \propto \frac{1}{\sqrt{d}}\]
(b) For \(3Fe_{(s)} + 4H_2O_{(g)} \rightleftharpoons Fe_3O_4_{(s)} + 4H_{2(g)}\), \(\Delta H = -150\ \text{kJ mol}^{-1}\) (exothermic):
- (i) Decrease in temperature: favours the exothermic forward reaction, so the equilibrium shifts to the right (more hydrogen).
- (ii) Increase in pressure: there are 4 moles of gas on each side, so pressure has no effect on the position of equilibrium.
- (iii) Removal of hydrogen: the equilibrium shifts to the right to replace the hydrogen removed.
(c)(i) Order (fastest first): Q (dust) > S (foil) > P (rod).
(ii) The rate depends on surface area. Zinc dust has the largest surface area exposed to the acid (fastest), the foil an intermediate area, and the rod the smallest surface area (slowest).
(iii) \[Zn + 2HCl \rightarrow ZnCl_2 + H_2\]
(d)(i) The pH of a solution is the negative logarithm to base ten of the hydrogen ion concentration, \(pH = -\log[H^+]\).
(ii)
- I. Neutralizing bench HNO3 with a base: the pH increases as H+ ions are removed.
- II. Diluting 25.0 cm3 of NaOH to 100.0 cm3: the pH decreases as the alkali becomes more dilute (lower [OH-]).
- III. Concentrating a solution of NaCl: the pH remains constant, because NaCl is a neutral salt and does not change [H+].
