Phase Diagrams Unit # 11

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?

We must know the names of the phase changes. 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 Point Liquid becomes a solid Freezing Point Gas becomes a liquid Condensation Point Liquid 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 point Normal Freezing point Boiling point of a substance at 1 atm 1 atm = 760 Torr, 760 mm Hg Water is 100 0C Normal Freezing point Freezing point of a substance at 1 atm Water 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 Pressure Every liquid has molecules evaporating and condensing at all times Force of the evaporating gas is called vapor pressure Vapor 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 Solvents Solutes The 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

READ THE LABELS ON THE GRAPH!!!!! 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?