1/6/2016
Chapter 9 Section 3
Review:
States of Matter
Solid
Liquid
Gas
Plasma
Typically as the temperature increases the matter changes
states.
Temperature
1
1/6/2016
Review:
Heat and Work
 Work is the change in Kinetic Energy.
 Total energy of a system is always conserved in a closed
system with no outside forces.
 Fd = W
 W = DKE
 DPE + DKE + DE = 0 ; conserved system
 W = Q (if there are no outside forces)
 Q =m cp DT
Definitions:
Phase Changes
 Heat, represented by the variable Q, is the transfer in
thermal energy which is measured in Joules.
 Heat always flows from hot to cold.
 Thermal Energy – the combined potential and
kinetic energy of the molecules in a substance
 Phase changes involve potential energy between
particles.
 There is NO temperature change while a substance is
changing phases
 Latent heat is the energy transferred as heat during a
phase change; either LF or LV
2
1/6/2016
Definitions:
Phase Changes
 Heat of fusion, LF, is the energy required to melt a
substance, goes into rearranging the molecules.
 Heat of vaporization, LV, is the energy required to
vaporize a substance, mostly goes into separating
the molecules.
 Specific heat capacity (cp) is the amount of energy
it takes to raise 1 kg of a substance 1° C.
Specific Heat
 If heat is added into a system the temperature will rise.
 What happens as heat is removed?
 If you know the heat, mass, and the temperature change
what can you calculate?
 Q = m cp DT
 cp = specific heat capacity of a material
 The larger the specific heat the more energy is needed
to change the substance temperature.
3
1/6/2016
Specific Heat Equations
Q = mcp∆T
Qf = mLf
Qv = mLv
Q = heat transferred (gained or lost)
m = mass of substance
cp = specific heat of substance
∆T = temperature change (Tf – Ti)
Lf = Heat of fusion = Lf
Lv = Heat of vaporization = Lv
Example from Page 319
How much heat is gained by raising the temperature of
10.0 grams of water from -25°C to 125°C?
4
1/6/2016
Example problem:
 How much heat is gained by raising the temperature of 10.0
grams of water from -25°C to 125°C?
 What phase is water in at -25°C? Solid (ICE)
3
 What is the specific heat of water in this phase? 2.09 x 10 J/(kg°C)
 What temperature does the phase change occur? 0°C
 What is the heat of fusion value for water? 3.33 x 105 J/kg
 What phase is after the heat of fusion? Liquid (WATER)
 What is the specific heat of water in this new phase?
4.186 x 103 J/(kg°C)
 What temperature is the next phase change? 100°C
 What is the heat of vaporization for water? 2.26 x 106 J/kg
 What is the specific heat of water in this last phase?
2.01 x 103 J/(kg°C)
QTOTAL = QA + QB + QC + QD + QE
QA = Q-25°C to 0°C
QB = QFusion
QC = Q0°C to 100°C
QD = QVaporization
QE = Q100°C to 125°C
=mcICEDT
=mHFusion
=mcWATERDT
=mHVaporization
=mcSTEAMDT
5
1/6/2016
Q = Q-25°C to 0°C
+ Qf
+ Q0°C to 100°C
+ Qv
+ Q100°C to 125°C
Example
6
1/6/2016
Thermal Equilibrium
 When the objects in a system are at the
same temperature the system is in
THERMAL EQUILIBRIUM
 When the objects have different
temperatures heat flows until thermal
equilibrium is reached.
7
1/6/2016
Latent Heat
Qf or Qv
 To have a ‘Change of Phase’ requires energy
 Latent heat is the energy required to change from one state
to an other.
 The temperature of the substance DOES NOT change until the
phase change is complete.
 Heat of Fusion – solid to liquid or the reverse– Lf
 Heat of Vaporization – liquid to gas or the reverse– Lv
 Typical values in the student textbook.
To find the specific heat capacities:
Use your textbook in Chapter 9 section 3
 Specific Heat Capacities Table Pg 316
 Latent Heat of Fusion and Vaporization Table Pg 320
 Appendix F Pg R41 (Specific Heat Capacities)
 Appendix F Pg R42 (latent heat capacities at STP)
 Peer reviewed (NSTA, ASME, ACS, AIP, & etc.) websites
8