Any graphs should be made using Excel with proper labeling of axes, units provided when applicable, a graph title, and any relevant information included on the graph. Take the value of R = 8.3141 K1 molt and 0 DC = 273.15 K.

Problem 1

The equilibrium constant was measured for a certain chemical reaction from 500 DC to 550 DC. The results are given below.

1. Determine from the data the value of  ΔrH°/ KJ mol¯¹, ΔrG°/ KJ mol¯¹, and ΔrS°/ JK¯¹ mol¯¹ at 500 K. State any approximation you make.
2. Estimate the values of ΔrH°/ KJ mol¯¹, ΔrG°/ KJ mol¯¹, and ΔrS°/ JK¯¹ mol¯¹ at 298 K. State any approximation you make.
3. How reliable is your estimate in (b)? Give a reason for your answer.

Problem 2

A pure unknown substance with a mass of 1.1186 g had an osmotic pressure of 426.371 kPa at 298 K.

1. What is the relative molar mass of the substance to the nearest integer in units of g mol¯¹? The same substance was observed to free at 17.748 °C. 1.7312 g of sugar (Mr = 342.3 g mol¯¹) was dissolved in 100 g of the substance and the freezing point measured again. This time the unknown substance froze out at 17.412 °C.
2. Calculate ΔfusHc of the unknown substance in kJ mol¯¹.

Problem 3

Two chemicals, A and B when mixed produced an almost perfect ideal solution. The vapour pressures of A and B were 25.4 kPa and 96.1 kPa respectively at 298 K.

1. Draw a pressure composition phase diagram for 298 K (full marks if drawn correctly in Excel). A solution containing a total of 20 mmol = nA + nB was prepared in a piston with the composition of zq = 0.6481. The total pressure on the piston was adjusted to 40.66 kPa.
2. Indicate on your phase diagram the compositions (xA, yA, zA) of the piston at the given pressure.
3. What are the total number of moles of A and the total number of moles of Bin the piston?
4. What is the number of moles of gas and the number of moles of liquid in the piston?
5. What is the number of moles of gaseous chemical A and liquid chemical A in the piston?
6. What is the number of moles of gaseous chemical B and liquid chemical B in the piston?
7. What is the approximate volume (in liters) of the piston? (hint: ignore the volume of the liquid).

Problem 4

A 1.1287% (weight percent) solution of salt with Mr = 162.5 g mol¯¹ was prepared at 25 °C. The density of the prepared solution was 1.00886 g cm¯³. The density of water at 25 °C is 0.99707 g cm¯³, and the density of the crystalline salt was 2.730 g cm¯³.

1. What is the molar volume of the crystalline salt?
2. Estimate the partial molar volume of the salt at infinite dilution.
3. Are (a) and (b) the same? Why?

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