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CHEMICAL THERMODYNAMICS PROBLEMS SENIOR FRESHMAN 2000-2001 ------------------------------Question 1. Calculate H at 900 K for the reaction 2A + B --------> A2B given the following information: A B A2B H300 formation (kJ mol-1) 0 -200.74 -313.65 Cp (J K-1 mol-1) 20.49 + 0.002 T 28.44 31.78 Question 2. A liquid which has a normal boiling point of 348.4 K has a latent heat of vapourisation of 35.42 kJ mol -1. Calculate the pressure under which this liquid would boil at 349.2 K. Question 3. Calculate the change in enthalpy, entropy and Gibbs free energy which occurs when one mole of carbon monoxide is heated from 300 K to 500 K at 1 atmospheric pressure. The molar heat capacity in J K -1 at this pressure is given by Cp = 26.537 + 7.6831 x 10-3 (T/K) – 11.72 x 10-7 (T/K)2 The molar entropy of carbon monoxide gas is 198.087 J K-1 mol-1 at 300 K and 1 atmosphere. Question 4. Calculate the solubility at 298 K of a substance which melts at 323 K and has a molar latent heat of fusion of 12.29 kJ mol-1 assuming ideal behaviour. Show how you derive the solubility equation that you use. Question 5. The molar heat capacity of a substance is given (in J K-1 mol-1) by the following equations Cp (s) = 15.473 x 10-5 T3 0 < T < 25 K Cp (s) = 4.3 x 10-5 T2 Cp (s) = 7.2 x 10-5 T 25 T < 125 K 125 T < 400 K H (fusion) at the melting point (125 K) is 1.881 kJ mol-1. Calculate the third law entropy of this substance in the liquid state at 250 K. Question 6. The reaction 2A + B 2AB takes place entirely in the gas phase. The equilibrium constant (Kp) at 750 K is 1.76 x 10-4 while at 825 K the Gibbs free energy change for the reaction is 56.888 kJ. What is the enthalpy change for this reaction in the 750 K to 825K temperature interval? Question 7. An organic solid which has a normal melting point of 343 K has a density of 1.42 g cm-3 and a vapour pressure of 933.2 Nm-2 at that temperature. At 373 K its vapour pressure is 2866.4 Nm-2. Also at the melting point the enthalpy of fusion is 19.65 kJ per mol and the density of the liquid 1.23 g cm-3. (i) (ii) (iii) (iv) NOTE: Calculate the enthalpy of vapourisation State the assumptions and approximations involved in the equation(s) used in (i) Estimate the heat of sublimation State whether the melting point under a pressure of 5.0 x 10 6 N m-2 would be greater or less than 343 K and explain your answer atmospheric pressure is 101325 Nm-2 1