Download Autumn Examinations 2009 - First Year Engineering Chemistry (CH106) Notes and more Exams Chemistry in PDF only on Docsity! Ollscoil na hÉireann, Gaillimh National University of Ireland, Galway _______________________________ AUTUMN EXAMINATIONS 2009 _______________________________ FIRST YEAR ENGINEERING CHEMISTRY (CH106) Professor Martin Wills, D. Phil (Oxon) Professor Paul V. Murphy Dr. N.W.A. Geraghty Time allowed: Three hours Answer five questions of which not more than two may be chosen from any one section. Separate answers books for Sections A, B, and C are not required Section A 1. Answer all parts (i) Explain what is meant by enthalpy change, ∆H, and, using two examples, why it is important from a practical point of view. [6 marks] (ii) The inertness of the metal aluminium is due to the formation of a very thin layer of aluminium oxide (alumina, Al2O3) on its surface: 2Al(s) + 3/2O2(g) → Al2O3(s) (a) Use the data provided below to calculate ∆S° and ∆G° for this reaction. ∆H°f Al2O3 (s) = -1,678.0 kJ mol-1 S° Al (s) = 28.3 J mol-1 K-1 S° O2 (g) = 205.0 J mol-1 K-1 S° Al2O3 (s) = 50.9 J mol-1 K-1 [10 marks] (b) Assuming ∆S and ∆H are independent of temperature, would you expect the reaction to be spontaneous at 400°C? Explain your answer. [4 marks] More on next page 2. Answer all parts (i) Explain what is meant by an orbital and, using an example, what information is required to describe an orbital completely. [5 marks] (ii) Describe the principal sub-atomic particles from which atoms are constructed and explain how any one of them was discovered. [5 marks] (iii) Draw a simple phase diagram for water and use it to explain how freeze drying works. [5 marks] (iv) Explain what is meant by ionization energy and account for the variations shown in the ionization energies (kJ mol-1) of the elements in the first row of the Periodic Table: Li, 519; Be, 900; B, 799; C, 1090; N, 1400; O, 1310; Ne, 2080 [5 marks] 3. Answer all parts (i) The metal magnesium can be produced industrially using the following reactions: Mg(OH)2 → MgO + H2O MgO + C → Mg + CO (a) Calculate the mass of carbon that would be required to produce 1 tonne of magnesium. [4 marks] (b) Calculate the volume of CO (at STP) that would be produced in processing 1 tonne of Mg(OH)2. [3 marks] (c) Calculate the mass of Mg that would be produced from 1 tonne of Mg(OH)2. [3 marks] [1 tonne = 1000kg; 1 mole of a gas occupies 22.4 L at STP] (ii) The following data were obtained for the reaction: 2NO + H2 → N2O + H2O Initial Concentration (mol L–1) Experiment NO H2 Initial Rate (mol L–1 s–1) 1 6.4 x 10–3 2.2 x 10–3 2.6 x 10–5 2 12.8 x 10–3 2.2 x 10–3 10.4 x 10–5 3 6.4 x 10–3 4.4 x 10–3 5.2 x 10–5 Determine (a) the overall order of the reaction, (b) its rate constant k, and (c) its rate when [NO] = [H2] = 1.5 x 10–2 mol L–1. [4 marks, 3 marks, 3 marks] More on next page
