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.
The equilibrium constant was measured for a certain chemical reaction from 500 DC to 550 DC. The results are given below.
- 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.
- 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.
- How reliable is your estimate in (b)? Give a reason for your answer
A pure unknown substance with a mass of 1.1186 g had an osmotic pressure of 426.371 kPa at 298 K.
- 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.
- Calculate ΔfusHc of the unknown substance in kJ mol¯¹.
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.
- 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.
- Indicate on your phase diagram the compositions (xA, yA, zA) of the piston at the given pressure.
- What are the total number of moles of A and the total number of moles of Bin the piston?
- What is the number of moles of gas and the number of moles of liquid in the piston?
- What is the number of moles of gaseous chemical A and liquid chemical A in the piston?
- What is the number of moles of gaseous chemical B and liquid chemical B in the piston?
- What is the approximate volume (in liters) of the piston? (hint: ignore the volume of the liquid).
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.
- What is the molar volume of the crystalline salt?
- Estimate the partial molar volume of the salt at infinite dilution.
- Are (a) and (b) the same? Why?