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 for a phase change such as 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. boiling. However, not too many 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 d) Using your answer to c) as the accepted value, calculate the % difference between it and the heat of vaporization at 25°C. 2. (9 pts) Calculate T, AU, AH, q, and w for the reversible adiabatic expansion of 3.75 mol of an ideal gas with Cv.m 2.5R. The initial conditions for the gas are 273.15K and 20.00L. The final volume is 100.OL. Underline each answer. 3. (8 pts) 6.00 mol of an ideal gas with Cv.m 1.5R undergo a two-step process. Calculate q, w, AU, and AH for each step and for the total process. Put your answers in the form of a table such as was shown in the lecture slides. Step A: Isothermal compression at 305K under a constant pressure of 10.0 bar from an initial pressure of 2.00 bar. Step B: After step A, the system is cooled at constant volume to 285K

Answer 1

CAH = DH°(paoduct) -Ds#'fpehah) ' vapizal 34274) th&lg/o)l (answves) /23)jlm k 42-8lo0od65 6- ho-2Kjmol d Freence 4 aKlm 6-138/ 6.M