8.3 Phase Transitions

What is a phase transition

A change in physical state (solid, liquid, gas)

List the 6 phase of transitions

Melting, freezing, vaporization, condensation, sublimation, deposition

What is vaporization

Liquid to gas

What is condensation

Gas to liquid

What is sublimation

Solid to gas

What is deposition

Gas to solid

What is dynamic equilibrium

When two opposite processes occur at equal rates

In liquid - gas equilibrium what two processes are equal

Vaporization and condensation

Does dynamic equilibrium mean molecules stop moving

No molecules continue moving constantly

What is vapor pressure

Pressure of gas above a liquid at equilibrium

How does temperature affect vapor pressure

Higher temperature means higher vapor pressure

How do intermolecular forces affect vapor pressure

Strong IMFs mean low vapor pressure; weak IMFs mean high vapor pressure

Why do strong IMFs lower vapor pressure

Molecules are held tightly so fewer escape into gas

what is boiling point

temperature where vapor pressure equals external pressure

what is normal boiling point

boiling point at 1 atm

relationship between IMFs and boiling point

strong IMFs mean higher boiling point

relationship between vapor pressure and boiling point

high vapor pressure means low boiling point

what is ΔHvap

energy required to convert liquid to a gas

is vaporization endothermic or exothermic

endothermic

is condensation endothermic or exothermic

exothermic

what is ΔHfus?

Energy required to convert solid to a liquid

Is melting endothermic or exothermic

exothermic

Is freezing endothermic or exothermic

Exothermic

What is ΔHsub

Energy required for solid to gas

Relationship between enthalpies:

ΔHsub = ΔHfus + ΔHvap

what happens to temperature during a phase change

It stays constant

why does temperature stay constant during phase changes

Energy is used to break/from IMFs not increase kinetic energy

What does a heating curve show

temperature vs heat added

what do sloped regions represent

temperature change

what do flat regions represent

phase changes

equation for temperature change

q = mcΔT

Equation for phase change

q = nΔH

which has higher vapor pressure: strong or weak IMFs

weak IMFs

which has higher boiling point: strong or weak IMFs

strong IMFs

why does sweating cool the body

evaporation absorbs heat from the body

Why is ΔHvap greater than ΔHfus

Vaporization requires completely breaking IMFs fusion only partially

During boiling why doesn’t temperature increase

Heat is used to overcome IMFs not increase kinetic energy

When do you use q = mcΔT?

when temperature changes (no phase change)

When do you use q = nΔH?

During phase changes.

What are the 5 steps in heating ice to steam?

1. Heat ice

2. Melt ice

3. Heat liquid

4. Boil liquid

5. Heat gas

Does increasing surface area affect vapor pressure?

No (only affects how fast equilibrium is reached).

What must happen for boiling to occur?

Vapor pressure = atmospheric pressure.

At higher altitude, boiling point is higher or lower?

Lower (because external pressure is lower).