Unit # 11

Phase Diagrams

What is a Phase Diagram?

A phase diagram shows the preferred physical states of matter at different temperatures and pressure.

Triple point is the intersection on a phase diagram between three phases The point at which all three states of a

substance are present

Terms to Know

Critical point The temperature and pressure at

which you can no longer tell the difference between a liquid and a gas.

It is where the liquid-gas line stops

Interpreting a Phase Diagram

What is point B? What is point C?

Phase Change Terms

We must know the names of the phase changes.

Which ones do we know already?

Changes of State

Solid becomes a liquid Melting PointLiquid becomes a solid Freezing PointGas becomes a liquid Condensation PointLiquid becomes a gas Boiling Point

Changes of State

Melting and Freezing Points are the SAME TEMPERATURE

Condensation and Boiling Points are the SAME TEMPERATURE

How do we identify the phases?

Interpreting a Phase Diagram

What is happening as you cross curve AB? What is happening as you cross curve BC? What is happening as you cross curve BD?

Let’s interpret the diagrams

Changing Phases

Normal Boiling pointBoiling point of a substance at 1 atm 1 atm = 760 Torr, 760 mm HgWater is 100 0C

Normal Freezing pointFreezing point of a substance at 1 atmWater is 0 0C

Changing Phases

During a phase change there is no change in temperature – the KE is used to spread or bring together the molecules of the substance

During a phase change there is only a change in potential energy

Heating curve – a plot of temperature versus time for a substance where energy is added at a constant rate

Heating Curve for Water

Vapor Pressure Graphs

Vapor PressureEvery liquid has molecules evaporating and

condensing at all timesForce of the evaporating gas is called vapor

pressureVapor Pressure Graphs show the boiling

point of liquids at different temperatures and pressures

Vapor Pressure Graphs

At what temperature does liquid A boil at a pressure of 500 mm Hg?

At what pressure does liquid B boil at 110°C?

Intermolecular Forces are forces that hold particles together

Which liquid has stronger intermolecular forces?

Solubility Curves

SolventsThe liquid you are dissolving something into

(ex. Water)Solutes

What you are trying to dissolve (ex. Sugar)Solubility Curves show how many grams

of solute you can dissolve in a specific amount of solvent at various temperatures

Solubility Curves

A specific amount of solvent?? How much is that???

READ THE LABELS ON THE GRAPH!!!!!

Solubility Curves Which is the most

soluble at 10°C? Which is least soluble

at 10°C? Which becomes less

soluble as temperature goes up?

Which solubility changes the least from 0-100°C?

How many grams of KClO3 can dissolve in 100g of water at 70°C?

In 200g of water?

Solubility Curves

Saturated Solution Contains the

maximum amount of solute that can be dissolved at the given temperature

If you have a saturated solution of KClO3 at 70°C, how much will precipitate at 30°C?