Question

When two volatile liquids (X and Y) are mixed, the solution process involves

1. breaking the intermolecular X---X and Y---Y attractions, and

2. forming new X---Y attractions.

Complete this table describing how the relative strengths of these attractive forces affect vapor pressure and enthalpy of solution, as zero, negative, and/or positive.

Strenght of the attractive forces	Raoult's law deviations	?H soln
X---X, Y---Y, and X---Y are equal
X---Y is strongest
X---Y is weakest

Answer 1

Case -3 The the attraction X-Y is weakest. That is the attractions X-X > X-Y and Y .ץ > X-Y In this case the initial attractions are stronger and more stable than the final attractions. This means thatinorder to make this unstable mixture we need to provide some heat or energy to the system. Thus, AH solution is positive. As the mixture is unstable it will have low boiling point, thus it has high vapor pressure. As vapor pressures are higher than ideal expected vapor pressures, its deviation from Roult's law is positive.

Answer 2

The liquids X and Y are volatile in nature. Initial attractions in the liquid X is X - X. Initial attractions in the liquid is Ý- On the mixing each other, the possible attractions are X-X, Y - Y Case -1 The interactions X- X, Y - Y and X- X are equal. This is an example for ideal solution. Even on mixing, there will be no change in the molecular attractions and heat neither evolved nor taken. Hence, the change in volume will be equal to zero and Raoult's law deviation is zero and AH solution is zero. and X-Y.

Case 2 The the attraction X -Y is strongest. That is the attractions X-X < X-Y and Υ-yX-y The attractions X- Y are stronger means that X -Y is stable bond when compared to X-X and Y-Y Boiling points of these attractions are larger than expected ideal boiling points. Boiling points are inversiley proportional to vapor pressure. So, the deviation from Raoult's law will be negative. Since, the final solution is more stable, it will surely be exothermic reaction. Thus, AH sol is negative.

Case -3 The the attraction X- Y is weakest. That is the attractions X - X>X- Y and Y-Y>X-Y In this case the initial attractions are stronger and more stable than the final attractions. This means thatinorder to make this unstable mixture we need to provide some heat or energy to the system Thus, AH As the mixture is unstable it will have low boiling point, thus it has high vapor pressure. As vapor pressures are higher than ideal expected vapor pressures, its deviation from Roult's law is positive. sohaton is positive.

Answer 3

1. zero
2. positive
3. negative