Chemical Thermodynamics

2. Water initially at 155°C is contained in a piston- cylinder assembly. The water undergoes a process to the corresponding saturated vapor state, during which the piston moves freely in the cylinder. There is no heat transfer with the surroundings. If the change of state is brought about by the action of a paddle wheel, determine the net work per unit mass in kJ/kg and the amount of entropy produced per unit mass in kJ/kg. [MO2]

Chemical thermodynamics in the manufacture of methanol Methanol (CH3OH) is used to manufacture a large number of important chemicals, such as formaldehyde (HCHO) which is employed in the manufacture of a variety of polymers; methyl-tertiary-butylether ((CH3)3OCH3), which has been used as a lead-free anti-knocking agent in petrol; acetic acid (CH3CO₂H), etc. Annual production of methanol has been increasing: from 3.3 MTe/yr in 1982¹ to 20 MTe/yr in 1991.² Methanol is manufactured using synthesis gas (a mixture of carbon monoxide, CO, and hydrogen, H₂) through the following chemical equilibrium. (a) Use the data in Table 1 to calculate the following. (i)The enthalpy change for the reaction, under standard conditions. Comment on your answer. (ii) The standard entropy change for the reaction. Comment on your answer. (iii) The standard Gibbs energy change for the reaction, under standard conditions. Comment on your answer. (iv) The equilibrium constant for the reaction equilibrium, under standard conditions. Comment on your answer. (v) The change in the heat capacity at constant pressure for the chemical reactions, under standard conditions.

2. Consider a 50/50 vapor mixture of n-pentane and n-hexane at 13 bar. Assume that the vapor phase can be well-described by the Peng-Robinson equation of state. a. At what temperature will the vapor begin to condense? What is the composition of the first drop of liquid. b. At what temperature will the vapor completely condense? What is the composition of the last drop of vapor?

(b) Assuming that the constant pressure heat capacities are independent of temperature, use your answers to part (a) to calculate the equilibrium constant for the reaction at 225, 300 and 450 °C, at standard pressure. Comment on your results.

1. Consider liquid water, water vapor, strong tea, and sweet tea (i.e., the strong tea with a bunch of sugar). Plot the chemical potential vs. temperature over a narrow range of temperatures near 100°C. Explain your rationale for the shape and relative position of each line. Plot the chemical potential vs. pressure over a narrow range of pressures near 1 bar. Explain your rationale for the shape and relative position of each line.

3. Hexane and heptane exist at vapor-liquid equilibrium. Initially a total of 50 mole % of the mixture is vapor, and 50 mole % is liquid. Hexane is added to the solution at constant temperature, but the mixture remains 50 mole% vapor. Has the pressure of the system increased, decreased, or remained the same? Explain.

2. Consider a pan of water being heated. Which method is a more efficient way of heating water? Explain. [MO1] a. By placing it on an electric range. b. By placing a heating element in the water.

8. Air dissolves in a liquid solvent so that the O₂ concentration in the solvent is three times that of the N₂ concentration. Compare the fugacities of O2 and N₂ dissolved in the solvent in the presence of air and explain the reason for your answer.

5. Water at 140°C and 10.0 bar expands through a throttle to 1.0 bar. What is the outlet temperature and how many phase(s) are in the effluent? Explain your answer.

1. Water, initially a saturated liquid at 160°C, is contained in a pistol-cylinder assembly. The water undergoes a process to the corresponding saturated vapor state, during which the piston moves freely in the cylinder. If the change of state is brought about by heating the water as it undergoes an internally reversible process at constant pressure and temperature, determine the work and heat transfer per unit mass in kJ/kg. [MO1]