28 9 This question is about the effect of temperature on the rate of decomposition of nitrogen(V) oxide. 2N2O5(g) → 2N2O4(g) + O2(g) (a) The diagram shows the Maxwell-Boltzmann distribution of molecular energies for nitrogen(V) oxide at a temperature T1 . Ea is the activation energy of this reaction. Energy, E Ea T1 (i) Give the label for the vertical axis. (1) .................................................................................................................................................................................................................................................................................... (ii) Draw a second curve on the same set of axes for the same gas at a lower temperature, T2. (2) (iii) Explain, in terms of collisions and energy, why lowering the temperature decreases the rate of reaction. (2) ..................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .............................................................................................................................................................................................................................................................................. ....... (iv) A catalyst is added to the gas. Label the diagram above with the symbol Ecat to show a possible activation energy for the reaction in the presence of a catalyst. (1) 29 (b) The rate constant for the decomposition of nitrogen(V) oxide was determined at two temperatures. Temperature / K Rate constant / s−1 328 1.50 × 10−3 338 4.87 × 10−3 Calculate the activation energy for this reaction. Include units and give your answer to an appropriate number of significant figures. You should not attempt to use any graphical method to answer this question. The Arrhenius equation relating two rate constants, k1 and k2 , at two different temperatures, T1 and T2 , can be expressed as ln k k E R T T 2 1 2 1 1 1    = − −     a (5) (Total for Question 9 = 11 marks) TOTAL FOR PAPER = 90 MARKS 30 BLANK PAGE 31 BLANK PAGE 32