Question

1. (8 pts) Virtually every pchem textbook has a table of enthalpy values for 25°C. One use for these may be to calculate the enthalpy fora phase change such as boiling. However, not t0o many compounds boil at 25°C. You are going to calculate the percent difference between the heat of vaporization of ethanol using data for 25°C and that at its boiling point of 78°C. a) Write the chemical equation that shows the vaporization of 1 mol of ethanol b) Using the following standard heats of formation at 25°C, calculate the heat of vaporization of 1 mol of ethanol at 25°C: AH°(EtOH, liquid) = -277.6 kJ/mol AH°(EtOH, gas) = -234.8 kJ/mol c) Using the following heat capacities, which you may take as constant over 25-78°C, calculate the heat of vaporization of ethanol at its boiling point of 78°C: Cp (EtOH, liquid) = 112.3 J/mol*K, Cp (EtOH, gas) = 65.6 J/mol*K ined with een it and the heat of d Using your answer to c) as the accepted value, calculate the % difference bet vaporization at 25°C.nner

Answer 1

Answexs- heat HOHI9) b) Heat of Vapourisaton feom above Eguatioh ate Can Say the clierence in Energy -23. l-217.6) 42.8 kJ/mol This Entra heat is the heat of vapoahigation. A Huap - Viguid heat tontent Sp xT V J 65.6 Js 351 K 93 110 3 J/mol lW. 3 x 351K mol K 39x lo Jmol 16 X103/mo AH= 16 KJ mol

49 at 95 c J (46. 7Jmol. k - 13 kJ/mol 16-15 )x Lo didference X loo 13 XIKS 3 x 10 O 2 13 2 23.08