1. The Heating Curve
Mr. Shields Regents Chemistry U07 L03

2. Phase Changes Let’s review what we’ve learned previously about
First … What is a phase
change?
A change from one state
of matter to another.
What does endothermic and exothermic mean?
Absorbs heat
/ Releases heat

3. Phase Change Overview
What are the names of the phase changes we’ve studied?
Gas
Solid
Liquid
Energy Absorbed
Energy Released
Endothermic
Exothermic a b c d e f
ENDOTHERMIC
Phase changes
EXOTHERMIC
Phase Chages a.
Sublimation d.
Deposition b.
Fusion e.
Condensation c.
Vaporization f.
Solidification

4. Phase Changes What actually happens to E as matter moves from
Solid  Liquid  Gas:
Energy is absorbed (endo)
Temp increases
KE increases
molecules move further apart
PE increases (Why?)
Remember … PE is a function of the position
of two bodies relative to one another
So … PE inc as molecular separation increases

5. Heating Curve What happens when we keep adding energy to a solid ?
Solid becomes a liquid then the liquid
becomes a gas
As this energy is added
KE inc and so does Temp.
but does temp Uniformly inc.
over time?
The answer is NO!

6. Heating Curve So what does happen if the temperature does not
Uniformly increase?
What happens is described by what is called
the HEATING CURVE

7. Heating Curve If we heat a solid it’s temperature increases
The energy needed to heat one gram of a
substance 1°C is the specific heat value (c)
for the substance.
This can be calculated from the slope of the
line when the temp. is increasing.

8. Steam Water Slope = Specific Heat Ice
and Ice
Ice
Water and Steam
Steam
-20 20 40 60 80
100
120
220
760
800
Heating Curve for Water
Steam
Water
Slope = Specific Heat
Ice

9. Heating Curve The temp. will continue to rise until we finally
reach the temperature at which the solid
begins to melt
It begins to go thru a phase change
solid  Liquid
This phase change is called melting

10. Solid/Liquid Phase Transition
As the solid begins to melt something
Unusual Happens.
As we continue to add heat to the solid
the temperature stops rising as the solid
continues to melt.
Solid
Melting Solid
But why does this happen?

11. Solid/Liquid Phase Transition
Solids exist in a rigid, closely packed, highly
structured pattern
Liquids however have no such rigid structure.
As we reach the solids m.p. there is just enough energy to
begin overcoming the intermolecular forces between
molecules holding them together
in the solid state...
Molecules begin to separate

12. Heat of Fusion Added additional heat energy goes into
Separating more and more molecules
As molecules move from solid to liquid the PE
Increases but since the temperature doesn’t rise
The KE remains constant.
The energy necessary to melt 1 GRAM of a
solid is called the …
It is unique for every substance.
HEAT OF FUSION (Hf)

13. Solid/Liquid Phase transition
Remember… heat ALWAYS flows from hot to cold
Until the last piece of solid melts the temperature the
Solid/liquid mixture remains constant
Once there’s no solid left all additional heat added
begins to increase the temperature of the liquid. H C

14. Solid/Liquid Phase transition
When heat is added what happens to KE, Temp. (T) & PE ?
Only a single solid (S) phase present
KE (T) increases
PE is Constant
Dual S&L Phase present
KE (T) is Constant
PE increase
Only a single liquid (L) phase present
PE is constant
Solid
S & L
Liquid
Heating curve

15. Liquid Phase transition
B.P
Once all the solid has turned to liquid, any
additional heat added
to the liquid increases
the Temp. until the boiling
Point (B.P.) is reached.
Then . . .
As in the transition from solid
to liquid, 2 phases are now present
& the Temp. of the boiling water remains constant
Solid
S & L
Liquid

16. Heat of Vaporization Molecules in the liquid phase form a close but
loosely organized structure
Molecules in the gas
Phase have no structure
And are widely separated.
To separate these molecules this much takes
lots of energy.
This energy is called the HEAT OF VAPORIZATION (Hv)
Liquid
S & L
Solid
Gas
L & G

17. Heat of Vaporization For water, Hv = 2,260 Joules/g Note Hv > Hf
As long as the liquid is boiling
T and KE will be
Constant
PE will Increase
as molecules
Move further apart
In the gas phase
Liquid &
gas
Solid &
liquid
M.P
B.P.
The Heating Curve

18. Summary (b.p.) T const. / KE const. /PE inc ( 2 phases )
T inc. / KE inc / PE Const.
( 1 phase )
T const. / KE const. /PE inc
( 2 phases )
Hf = J/g
(m.p.)
(b.p.)
Hv = 2,260 J/g

19. Cooling Curve The opposite of a heating Curve is a COOLING CURVE.
Brrrrr…
Since the sample is cooling it must be releasing heat.
As Temp decreases KE decrease and as a sample goes from gas
To liquid to solid the PE must be decreasing.

20. Cooling Curve Phase I: T decreasing KE decreasing PE constant
Phase II: T constant
KE constant
PE decreasing
Phase III: T decreasing
Phase IV: T constant
Phase V: same as I and III
Gas & Liquid
Liquid
solid
Liquid & solid
I II III IV V
Gas
Condensation
freezing
Note: This is the mirror image of a heating curve

21. STOP this is the end of the notes for p. 17-19

22. Specific Heat where ΔT = (Tf – Ti)
The SPECIFIC HEAT of a substance is the amount
of heat required to raise the temperature of 1 g of the
material by 1°C.
Each substance has it’s own unique specific heat…
The lower the specific heat the better the conductor
And …. q = m x C x ΔT
where ΔT = (Tf – Ti)

23. Specific Heat One of the variables in Specific heat calculations
Involves Temperature
Change.
What phases of the
The heating curve
Involve changes in T?
Phase 1, 3, 5
The Heating Curve
Phase V
Phase III Phase IV
Phase 1 Phase II

24. Specific Heat It’s in these phases that specific heat calculations
are used to determine how much heat us needed
to raise the temperature
of the sample
But how do we find
the heat necessary to
to fully melt or vaporize
a sample of matter
In regions where T does
Not change (phase II & IV)
The Heating Curve
Phase 1 Phase II
Phase III Phase IV
Phase V