I N T E R P R E T I N G G R A P H S W I T H P H A S E C H A N G E S

C H E M I S T R Y 3 0 S - P H Y S I C A L P R O P E R T I E S O F M A T T E R

H E AT I N G C U R V E• Shows the heating of a substance over time

Why is there a plateau?

W H Y T H E P L AT E A U ?

• In order for ice to melt, energy is needed to overcome the intermolecular forces of attraction.

• The temperature does not increase until all the intermolecular forces have been broken.

• However, at the plateau, there is an equal rate of melting and freezing called dynamic equilibrium.

C O O L I N G C U R V E

• S A M E R E A S O N A S H E AT I N G C U R V E B U T O P P O S I T E E F F E C T.

• PA RT I C L E S H AV E T O M O V E C L O S E R A N D T H E E N E R G Y I S R E L E A S E D U N T I L A L L L I Q U I D T U R N S I N T O S O L I D

VA P O R I Z AT I O N

• Vaporization is the general term to describe a liquid changing into the gas state

Boiling Evaporation

• Occurs on the surface of the liquid

• Occurs below boiling temperature

• Requires heat

B O T H A R E A F F E C T E D B Y T H E VA P O U R P R E S S U R E O F T H E L I Q U I D A N D T H E

AT M O S P H E R I C P R E S S U R E

• Occurs at boiling temperature

W H AT I S VA P O U R P R E S S U R E ?

• Formal definition: The amount of pressure the vapour above exerts on the liquid in a closed system.

S I M P L I F I E D V E R S I O N

Imagine the molecules at the surface of the liquid are constantly “pushing” to get out

into the gas phase

But they can’t push out because there are also air

molecules from the atmosphere pushing down

on them.

• Evaporation occurs when the molecules on the surface gains energy from the surroundings to enter the gas phase.

Boiling on the other hand, uses energy to overcome the intermolecular forces to enter the gas phase

• In a closed system, molecules in liquid will evaporate until equilibrium.

• The gas molecules exerts a pressure back on to the liquid and also the mercury in the closed system tube.

• The more mercury it can push, the more pressure the vapour has, meaning the more likely the liquid can evaporate.

Some substances evaporate ‘easier’ (or at a lower temperature) because they have a higher vapour pressure.

*They can “push out” with more force.

However, if the atmospheric pressure drops (the amount of pressure sitting on the surface), liquids can boil with less energy, their boiling point drops.

Y I P P Y ! W E A R E

F R E E !

T H E R E A R E N ’ T T H AT M A N Y O F T H E M . W E C A N G O

T H I S L I N E R E P R E S E N T S T H E S TA N D A R D AT M O S P H E R I C

P R E S S U R E

L I Q U I D S B O I L W H E N T H E I R

VA P O U R P R E S S U R E

I N T E R S E C T S W I T H T H E

AT M O S P H E R I C P R E S S U R E

P R O PA N O N E B O I L S AT 5 5 C

W H AT H A P P E N S W H E N T H E

AT M O S P H E R I C P R E S S U R E

D R O P S ?

WAT E R N O W B O I L S AT ~ 8 3 C I N S T E A D O F 1 0 0 C

W H AT S TAT E I S E T H A N O L I N W H E N I T I S AT 7 5 C ?

T H E VA P O U R P R E S S U R E I S B E L O W T H E AT M O S P H E R I C

P R E S S U R E , I T S TAY S I N L I Q U I D P H A S E

W H AT T E M P E R AT U R E I S R E Q U I R E D F O R B O I L I N G ?

A B O U T 9 3 C