Phase Equilibrium and Vapor Pressure Concepts

The video tutorial covers phase equilibrium, explaining how a dynamic equilibrium is established between different physical states of a pure substance in a closed system. It introduces key terms such as volatile, ideal solution, mole fraction, and partial pressure, which are essential for understanding Raoult's Law. Raoult's Law is then explained, showing how the partial vapor pressure of a component in an ideal solution is calculated. An example calculation is provided using hexane and heptane to demonstrate the application of Raoult's Law. The video concludes with a discussion on boiling points, composition diagrams, and their relevance to fractional distillation.

What is phase equilibrium?

• A static balance between two chemical reactions

• A dynamic balance between different physical states of a substance

• A state where only liquid exists

• A condition where no evaporation occurs

What factors affect the vapor pressure of a pure liquid?

• Both the nature of the liquid and the temperature

• Only the nature of the liquid

• Only the temperature

• The amount of liquid present

Which of the following best describes an ideal solution?

• A solution with no intermolecular forces

• A solution where intermolecular forces are the same as in pure liquids

• A solution where intermolecular forces are different from pure liquids

• A solution that cannot evaporate

According to Raoult's Law, the partial vapor pressure of a component in an ideal solution is equal to:

• The total pressure of the solution

• The mole fraction of the component divided by the total pressure

• The vapor pressure of the pure liquid multiplied by the mole fraction of the component

• The sum of all component pressures

In the example of hexane and heptane, what is the total vapor pressure of the solution?

• 20.5 kPa

• 13.3 kPa

• 3.05 kPa

• 10.25 kPa

What is the mole fraction of hexane in the vapor phase of the hexane-heptane mixture?

• 0.771

• 0.229

• 0.5

• 0.3

When does a liquid boil according to the video?

• When its vapor pressure is equal to the external pressure

• When it is mixed with another liquid

• When its temperature is below freezing

• When its vapor pressure is less than the external pressure

How does adding a non-volatile solute affect the boiling point of a solution?

• It has no effect on the boiling point

• It increases the boiling point

• It decreases the boiling point

• It makes the solution evaporate faster

What does the red line in a boiling point composition diagram represent?

• The pressure changes with temperature

• The freezing point of the solution

• The vapor composition

• The boiling point changes with composition

In a boiling point composition diagram, what does a higher mole fraction of a more volatile component indicate?

• A higher freezing point

• No change in boiling point

• A lower boiling point

• A higher boiling point