University of Waterloo Term Test 2 Chemistry 254: Thermodynamics Tuesday 6 July 2011 8:30-9:20 AM NAME .................................……………................................ I.D. ................................................…............…………..… INSTRUCTIONS (1) Answer ALL the questions, and do the easy ones first. The weight of each question is given in the table below. (2) A standard, non-programmable calculator is allowed. (3) Total time permitted for this examination is 50 minutes. (4) The data sheet is given on the last page of this exam paper. NOTE Be sure to present your work logically and neatly, and cross-off any rough work that you do not want the marker to see. Marks will be deducted for messy, disorganized presentation. SCORE Question 1 /5 Question 2 /5 Question 3 /5 Question 4 /5 Total /20 Please hand in this exam paper. Be sure to PRINT your name and ID on both. WARNING: Cheating in exam is considered to be the most serious academic misconduct and is ground for expulsion at the University of Waterloo. Don’t do it! Page 1 1. (a) Liquid water at 100C is in equilibrium with water vapour at 1 atm pressure. If the enthalpy change associated with the vaporization of liquid water at 100C, i.e. H, is 40.60 kJ mol-1, what is G and S? (b) Suppose that liquid water at 100C is in contact with water vapour at 0.900 atm. Calculate S and G for the vaporization process. Hint: Consider the additional entropy change for the expansion of the water vapour from 1 atm to 0.900 atm (assuming ideal gas behaviour for water). Also assume that H has not changed in this process. Page 2 2. The melting point of water at 1 atm is 0C and the enthalpy of fusion is 6.0095 kJ mol-1. The boiling point is 100C and the enthalpy of vaporization is 40.6563 kJ mol-1. The molar heat capacity CP,m for H2O is 75.291 J K-1 mol-1. Calculate S for the transformation of H2O(s, 0C) H2O(g, 100C). Express your answer in J K-1. Page 3 3. (a) One mole of an ideal gas is expanded reversibly and isothermally from 10 L to 20 L. Calculate S. Express your answer in unit of J K-1. (b) One mole of an ideal gas is expanded reversibly and isothermally from 1.00 bar to 0.100 bar. Calculate S. Express your answer in unit of J K-1. Page 4 4. Consider a system consisting of 1.5 mol CO2(g), initially at 15C and 9.0 atm and confined to a cylinder of cross-section area 100.0 cm2. The sample is allowed to expand adiabatically against an external pressure of 1.5 atm until the piston has moved outwards through 15 cm. Assume that CO2 may be considered as an ideal gas with CV,m = 28.8 J K-1 mol-1. Calculate q, w, U, T, and S. Express your answers in J, K or J K-1, where appropriate. END F TEST Page 5 DATA SHEET – For convenience, you may tear off this sheet and use it during the exam period. There is no need to hand in this sheet at the end of the exam. You may keep it or trash it. Equations and Constants Constants R = 1.9872 cal mol-1 K-1 = 8.3145 J mol-1 K-1 = 0.082057 atm L mol-1 K-1 = 0.083145 bar L mol-1 K-1 = 8.3145 Pa m3 mol-1 K-1 = 62.364 torr L mol-1 K-1 0C = 273.15 K General equations U U dU dT dV T V V T U P T P V T T V For a (monatomic) ideal gas P nRT V and CP 5 R n 2 For a van der Waals gas P and nRT n 2a 2 V nb V and U 0 V T CP CV R n n n 2a U 2 V T V The thermodynamics magic square T G A V P H U S Page 6

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