(a)(i) Explain what is meant by an effective collision
(ii) What does each term represent in the following expression? \(\Delta G\) = \(\Delta H\) — T\(\Delta\)S
(iii) What deduction can be made about a system given that the value of its \(\Delta\)G is zero?
(b)(i) State Le Chatelier's principle.
(ii) Suggest three conditions necessary for maximum yield of A\(_2\)B in the reaction represented by the following equation 2A\(_{2(g)}\) + B\(_{2(g)}\) \(\rightleftharpoons\) 2A\(_2\)B\(_{(g)}\) \(\Delta\)H = xkj.
(iii) Write an expression for the equilibrium constant of the reaction in (b)(ii) above.
(c)(i) Give the reason why a log of wood of a given mass does not burn out as quickly as sawdust of the same mass, under the same conditions.
(iii) List two examples of chemical reactions that are catalyzed by light
(a)(i) An effective collision is a collision between reacting particles in which the particles possess energy equal to or greater than the activation energy and collide with the correct orientation, so that a chemical reaction actually takes place.
(ii) In \(\Delta G = \Delta H - T\Delta S\):
- \(\Delta G\) = the change in Gibbs free energy of the system.
- \(\Delta H\) = the change in enthalpy (heat content) of the system.
- \(T\) = the absolute temperature (in kelvin).
- \(\Delta S\) = the change in entropy (degree of disorder) of the system.
(iii) If \(\Delta G = 0\), the deduction is that the system is at equilibrium (the reaction is neither spontaneous in the forward nor in the reverse direction).
(b)(i) Le Chatelier's principle: when a system in dynamic equilibrium is subjected to a change in temperature, pressure or concentration, the equilibrium shifts in the direction that tends to oppose (reduce) the effect of that change.
(ii) For \(2A_{2(g)} + B_{2(g)} \rightleftharpoons 2A_2B_{(g)}\), \(\Delta H = x\,kJ\) (taking the forward reaction to be exothermic), three conditions for maximum yield of \(A_2B\):
- Low temperature (favours the exothermic forward reaction).
- High pressure (3 moles of gas on the left change to 2 moles on the right, so high pressure shifts the equilibrium to the side of fewer gas molecules).
- Continuous removal of \(A_2B\) as it is formed (and/or use of a catalyst to attain equilibrium faster).
(iii) Equilibrium constant expression:
\[K_c = \frac{[A_2B]^2}{[A_2]^2\,[B_2]}\]
(c)(i) A log of wood burns more slowly than the same mass of sawdust because the sawdust is finely divided and therefore has a much larger surface area exposed to air (oxygen); the rate of reaction increases with surface area, so the sawdust burns out faster.
(iii) Two reactions catalysed by light: the photosynthesis of glucose in green plants, and the reaction of hydrogen with chlorine (or the substitution reaction of methane with chlorine).
(a)(i) An effective collision is a collision between reacting particles in which the particles possess energy equal to or greater than the activation energy and collide with the correct orientation, so that a chemical reaction actually takes place.
(ii) In \(\Delta G = \Delta H - T\Delta S\):
- \(\Delta G\) = the change in Gibbs free energy of the system.
- \(\Delta H\) = the change in enthalpy (heat content) of the system.
- \(T\) = the absolute temperature (in kelvin).
- \(\Delta S\) = the change in entropy (degree of disorder) of the system.
(iii) If \(\Delta G = 0\), the deduction is that the system is at equilibrium (the reaction is neither spontaneous in the forward nor in the reverse direction).
(b)(i) Le Chatelier's principle: when a system in dynamic equilibrium is subjected to a change in temperature, pressure or concentration, the equilibrium shifts in the direction that tends to oppose (reduce) the effect of that change.
(ii) For \(2A_{2(g)} + B_{2(g)} \rightleftharpoons 2A_2B_{(g)}\), \(\Delta H = x\,kJ\) (taking the forward reaction to be exothermic), three conditions for maximum yield of \(A_2B\):
- Low temperature (favours the exothermic forward reaction).
- High pressure (3 moles of gas on the left change to 2 moles on the right, so high pressure shifts the equilibrium to the side of fewer gas molecules).
- Continuous removal of \(A_2B\) as it is formed (and/or use of a catalyst to attain equilibrium faster).
(iii) Equilibrium constant expression:
\[K_c = \frac{[A_2B]^2}{[A_2]^2\,[B_2]}\]
(c)(i) A log of wood burns more slowly than the same mass of sawdust because the sawdust is finely divided and therefore has a much larger surface area exposed to air (oxygen); the rate of reaction increases with surface area, so the sawdust burns out faster.
(iii) Two reactions catalysed by light: the photosynthesis of glucose in green plants, and the reaction of hydrogen with chlorine (or the substitution reaction of methane with chlorine).
