Download First Year Engineering Exam Questions - Summer 2008 - Chemistry 1 & 2 (CH106) and more Exams Chemistry in PDF only on Docsity! 1 Ollscoil na hÉireann, Gaillimh National University of Ireland, Galway _______________________________ SUMMER EXAMINATIONS 2008 _______________________________ FIRST YEAR ENGINEERING CHEMISTRY 1 & 2 (CH106) Professor Martin Wills, D. Phil (Oxon) Professor Patrick McArdle Dr. Niall 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 Number of pages (including this one): 5 Section A 1. Answer all parts: (a) Explain what is meant by ∆H and, using two examples, explain why it is of great practical importance. [6 marks] (b) Using the data provided below determine the standard entropy change (∆S°) for the following reaction: CaO(s) + SO3(g) → CaSO4(s) [8 marks] ∆H°f (kJmol-1) ∆G°f (kJmol-1) CaSO4(s) -1432.7 -1320.3 CaO(s) -635.5 -604.2 SO3(g) -395.7 -371.1 (c) Explain why the sign of the entropy change is appropriate for this reaction. [2 marks] (d) Use the available data to estimate the temperature at which the reaction changes from being non-spontaneous to being spontaneous. Explain what assumptions are involved in making this estimate. [4 marks] 2 2. Answer all parts: (a) List three of the assumptions on which the Kinetic Theory of Gases is based, and use the equation derived from them (PV = 1/3 nmc2) to deduce Boyle’s Law. [5 marks] (b) Explain what is meant by ionization energy (IE) and why the following values are obtained as electrons are removed successively from a magnesium atom: 1st IE : 737.7; 2nd IE : 1450.6; 3rd IE : 7732.6 kJmol-1 [5 marks] (c) Explain the difference between an orbit and an orbital and how a 2py and a 3s orbital are related to each other. [5 marks] (d) Using any example explain how a heterogeneous catalyst works. [5 marks] 3. Answer all parts: (a) It has been suggested that the nitrogen dioxide (NO2) produced by supersonic aircraft flying at very high altitude may be having a negative effect on the ozone layer due to the following reaction: NO2 + O3 → NO3 + O2 The following data was collected for this reaction at 25°C. Initial Concentration Experiment NO2 (molL-1) O3 (molL-1) Initial rate of reaction (molL-1s-1) 1 2 3 5 x 10-5 5 x 10-5 2.5 x 10-5 1 x 10-5 2 x 10-5 2 x 10-5 0.022 0.044 0.022 (i) Determine the overall order of the reaction [4 marks] (ii) Calculate the rate constant, k [3 marks] (iii) Calculate the rate of the reaction when [NO2] and [O3] are both 2 x 10-7 molL-1 [3 marks] (b) Chromium metal is produced from potassium chromate (K2CrO4) in a two-stage process 2K2CrO4 + 2C → K2CO3 + K2O + CO(g) + Cr2O3 Cr2O3 + 2Al → Al2O3 + 2Cr (i) Calculate the mass of chromium that can be obtained from 1 tonne (1000kg) of K2Cr2O4 [4 marks] more on next page.....
