SCH4U Changes in Matter and
Energy
Calorimetry
P Page 300 # 1-5 (Systems and Surroundings)
P Page 302 # 8-13 (q=mcÄT)
P Page 304 # 14, 15 (Endo, Exothermic, ÄH)
Thermodynamics Terminology
Energy
• capacity to do work
Kinetic Energy
• energy that something has because it is moving
Potential Energy
• energy that something has because of its position
Thermochemistry Terminology
exothermic - reaction that gives off energy
endothermic - reaction that absorbs energy
chemical energy - energy associated with a
chemical reaction
thermochemistry - the quantitative study of
the heat changes accompanying chemical
reactions
thermodynamics - the study of energy and its
transformations
Thermodynamics Terminology
System: the part of the universe under
investigation
Surroundings: the rest of the universe
Universe = System + Surroundings
Thermodynamic System
Energy Units
!
!
!
!
calorie - energy required to heat 1 g of water by
1oC
Calorie - unit of food energy; 1 Cal = 1kcal
Joule - SI Unit
4.184 J = 1 calorie = 1 kg*m2 s-2
Specific Heat
• the amount of heat necessary to raise the
temperature of 1 gram of the substance 1 oC
• independent of mass
• substance dependent
• Symbol c
• Specific Heat of Water = 4.184 J/goC
Heat
q = m * c * DT
where
q => heat, J
m => mass, g
c => specific heat, J/(g* oC)
DT= change in temperature, oC
Molar Heat Capacity
• the heat necessary to raise the temperature
of one mole of substance by 1 oC
• substance dependent
• C
q = n * C * DT
Heat Capacity
• the heat necessary to raise the temperature
1 oC
• mass dependent
• substance dependent
• C
Heat Capacity
C=m*c
where
C => heat capacity, J/oC
m => mass, g
c => specific heat, J/ goC
Bomb Calorimeter
Changes of State
!
!
Temperature doesn’t change during a change of
state
Energy goes to overcome intermolecular
attractions
!
Heat of vaporization or condensation ÄHvap
!
Heat of fusion or solidification ÄHfus
!
No Temperature term in the calculation
!
Q = mÄHvap
Water molecules are polar molecules. Water
has a special type of intermolecular bond
called a Hydrogen Bond. The polar oxygen in
.
one water molecule forms a hydrogen bond
with the polar hydrogen in another water
molecule
dInter
molecular forces
d+
Ice molecules are locked in
fixed positions, held by
intermolecular bonds.
Ice is less dense than liquid
water because the molecules are
Are farther apart than in liquid
water.
Energy Requirements for changing state:
In ice the water molecules are held together b
Intermolecular forces.
The energy required to melt 1 mole of a substance is called t
molar heat of fusion
(DHfus ) For ice it is +6.02 kJmol
The energy required to change 1 mole of a liquid to its vapor is
molar heat of vaporization
called the
(D Hvap
) For water it- is +40.6 kJmol
D H (delta H)
is the change in energy or heat content.
It takes more energy to vaporize water than to melt it.
This is because in melting you weaken the intermolecular forc
of the hydrogen bonds are broken.
Here about 1/6
In vaporization you totally break them.
All the hydrogen bonds are broken
DH
vap
is always greater than
DH fus
Fusion is when a solid melts to form a liquid
Vaporization is when a liquid evaporates to form a gas.
Calculate the total quantity of heat evolved when
10.0g of steam at
200
C is
condensed, cooled , and frozen to ice at -50
C.
Calculate the total quantity of heat evolved when 10.0g of ste
condensed, cooled , and frozen to ice at -50
C.
The specific heat capacity of ice and steam are 2.06J/g C and
2.03J/g C respectively.
1
2
3
4
5
F-E = temperature falls until liquid starts to condense.
Gas particles lose kinetic energy.
steam
Q = mcÎT
1
Q = (10.0g)(2.03J/g C)(100 C)
Q = 2030J = 2.030kJ
1
E-D = Gas starts to condense: turning from gas to liquid. Th
temperature remains constant as energy is released to make
Inter-molecular forces.
H2O (i) ® H2O (g) energy required
@ 41 kJ/mol
100ºC
n(H2O) = mass / molar mass
2
= 10.0g / 18g mol -1
= 0.56 mol H 2O
vap
vap
H (H2 O) = 40.6kJ/mol
H (H2 O) = 0.56 mol x 40.6 kJ/mol = 22.7 kJ
2
D-C = temperature starts to decrease once all
Particles lose kinetic energy.
Liquid
water
3
Q = mcÎT
Q = (10.0g)(4.18J/g C)(100 C)
Q = 4180J = 4.180kJ
3
B-C = Solid starts to change state from liquid to solid.
Temperature remains constant as energy is released to form
Intermolecular bonds.
H2O (s)® H2O (i) energy required
@
6 kJ/mol
0ºC
n(H2O) = mass / molar mass
4
= 10.0g / 18g mol -1
= 0.56 mol H 2O
fus
fus
H (H2 O) = 40.6kJ/mol
H (H2 O) = 0.56 mol x 6.02 kJ/mol = 3.36 kJ
4
Heating and cooling curve for water heated at a constant rates.
A - B = Solid ice, temperature is decreasing.
Particles lose kinetic energy, vibration of particles decreases.
Ice
5
Q = mcÎT
Q = (10.0g)(2.06J/g C)(50 C)
Q = 1030J = 1.030kJ
5
Calculate the total quantity of heat evolved wh
at 200 C is condensed, cooled , and frozen
Total heat = 2.030kJ + 22.7 kJ + 4.180kJ +3.36 kJ
+1.03 kJ
= 33.3kJ