Thermal chemistry is study of the transfer of heat in
chemical reactions and physical changes.
Student will learn:
1. to read Phase diagrams
2. math calculations of energy for melting,
freezing, vaporization, condensing or
raising temperature of a compound or
element.
Thermal Chemistry
Phase: any part of a system that has
uniform composition and properties. ( solid, liquid,
gas)
Overhead
Fluid: gas or liquid: a substance that can flow and
take shape of the container.
Diffuse: ability to mix with other liquids or gases (p.364 food
coloring, perfume)
Vaporization: process - liquid or solid changes into a gas.
“you have added energy and vaporized it”
Evaporization: process - particles escape from the surface
of a non boiling liquid and become gas. “naturally evaporated”
Volatile liquids: liquids that evaporate readily “finger nail polish remover”
Condensation: process which a gas becomes a liquid
“ rain, water drops on out side of glass of cold drink”
Boiling: conversion of a liquid to a gas
within the liquid as well as the surface.
Boiling Point: Temperature which vapor pressure of the liquid
equals the atmospheric pressure.
Freezing or solidification: physical change of liquid to a solid
by removal of heat or energy
Freezing Point: Temperature which liquid and solid have
same average kinetic energy.
Melting: physical change of a solid to a liquid
by the addition of energy.
Melting point: the temperature at which a
solid becomes a liquid.
Sublimation: change of a solid directly to a gas.
“CO2.. Dry ice, Iodine, frost free freezer”
Deposition: change of a gas directly to a solid.
“ frost on grass or car windshield ”
Phase Diagrams
graph which shows conditions of phase changes
Triple point
= solid, liquid, gas coexist at equilibrium.
Critical Temperature point =
cannot exist as a liquid regardless of pressure.
o
The critical temperature point of water is 373.99 c. Above this
temperature, water cannot be liquefied, no matter how much
pressure is applied.
Critical Pressure point = lowest pressure at which the
substance can exist as liquid @ critical temp.
The lowest pressure at which water can exist as a liquid is
217.75 atm @ the critical temperature point.
Phase Diagram
Describe all phase changes that would occur when heating the chemical
from -80o to 20o at a constant pressure of 10atm.
At room temperature what is the phase of this chemical?
Phase Diagram
What are the phase changes at 16atm from -100o to 40o and their
corresponding temperatures?
At room temperature what is the phase of this chemical?
Phase Diagram
Given a sample of this chemical, how would you phase change the liquid
into a gas without changing the temperature?
Where is the triple point?
Where is the critical point?
Thermal Chemistry
study of transfer of heat in chemical reactions and
physical changes.
What is the difference?
Temperature
Heat
Thermal energy
Temperature: measurement of motion…
measurement of kinetic energy of the molecules
…. Wood…
…. cold (vs) hot water
……. Fever of 105
Normally use a thermometer
Heat: The transfer of thermal energy. The energy that ‘flows’
from higher Temperature to lower temperature.
… standing beside the burning wood and feeling the warmth…
Thermal energy = total energy of matter…
measured in joules…
Q = thermal energy
Heat of Fusion: energy required to melt solid to a liquid
Q = m Hf
Q = energy
M = mass
Hf = heat of fusion
Heat of Vaporization: energy required to vaporize a liquid
Q = m Hv
Q = energy
m = mass
Hv = heat of vapor
“ look on your chemistry tables”
Specific Heat = amount of energy required to raise 1gram of
substance 1 degree of temperature.
Q = m Cp t
“ look on your chemistry tables”
1.
Calculate the amount of energy required to melt a small
ice cube weighing 24 grams.
2.
Calculate the amount of energy required to produce
steam from 100 mL of water.
3. Find the molar heat of vaporization for a substance, given
that 4.22 mol of the substance absorbs 32.8 kJ of energy
when it changes from a liquid to a gas.
4. Aluminum is used in manufacturing Pepsi-cola cans.
How much heat energy does the factory need to provide to
melt the 3 grams of aluminum needed per can? The
factory produces 3,000 cans per hour. How much energy
is needed per hour? Aluminum’s melting point is 660
degrees Celsius.
Specific Heat = amount of energy required to raise 1gram of
substance by 1 degree
Q = m Cp
t
Looking at the chart of specific heat….
Which requires the most heat to heat up?
iron pipe or lead pipe
Which requires least amount of heat to heat up?
magnesium or gold
Which requires least amount of heat to heat up?
Fe,
Zn,
Ti
How much heat is needed to raise the temperature of a 20g
aluminum Pepsi-cola can 35 degrees?
2.
Calculate the heat lost from a 5g copper penny if
o
o
cooled from 25 c to 3 c in the freezer.
3.
Calculate the mass of water that uses 2508J of
energy in raising its temperature from 80oC to
100oC.
4.
Calculate the temperature rise if 224.25J of heat
energy was added to a 30gram ice cube.
*
HEATING CURVES
VS
COOLING CURVES
HANDOUT CURVE SHEET
label
60oc
50oc
40oc
30oc
20oc
10oc
0c
-10oc
-20oc
-30oc
0 kj
25 kj
50 kj
75 kj
100kj
125kj
150kj
175kj
200kj
225kj
250kj
Heating-Cooling curve ( Enthalpy of Fusion and Vaporization
Theory pt.1: The quantity of heat absorbed to melt a solid = the
quantity of heat released to solidify the liquid.
60oc
50oc
40oc
30oc
20oc
10oc
0c
-10oc
-20oc
-30oc
0 kj
25 kj
50 kj
75 kj
100kj
125kj
150kj
175kj
200kj
225kj
250kj
Theory pt.2: The quantity of heat absorbed to vaporize a liquid =
the quantity of heat released to condensate the vapor.
60oc
50oc
40oc
30oc
20oc
10oc
0c
-10oc
-20oc
-30oc
0 kj
25 kj
50 kj
75 kj
100kj
125kj
150kj
175kj
200kj
225kj
250kj
Theory pt.3: All solids absorb heat as they melt . This causes a
phase change rather than a temperature change.
60oc
50oc
40oc
30oc
20oc
10oc
0c
-10oc
-20oc
-30oc
0 kj
25 kj
50 kj
75 kj
100kj
125kj
150kj
175kj
200kj
225kj
250kj
Ex) ice melting: Temperature remains constant until all ice has
melted….. The temperature of water will increase only after all ice
has melted.
Ex) boiling water.
Which segments on the curve represent constant temperature?
What is the boiling point of this substance?
How much energy is needed for vaporization?
If this chart is based on 2 grams of substance how much energy is
needed to melt 10 grams of the substance.
60oc
50oc
40oc
30oc
20oc
10oc
0c
-10oc
-20oc
-30oc
0 kj
25 kj
50 kj
75 kj
100kj
125kj
150kj
175kj
200kj
225kj
250kj
At what temperatures does phase changes occur?
Which portion represents an decrease in heat absorbed and potential
energy decreases while Kinetic energy remains constant?
How much is the Heat of Vaporization?
At what temperature is condensation?
60oc
50oc
40oc
30oc
20oc
10oc
0c
-10oc
-20oc
-30oc
0 kj
25 kj
50 kj
75 kj
100kj
125kj
150kj
175kj
200kj
225kj
250kj
TIME
2
4
6
8
10
12
14
16
18
20
22
24
26
28
29
30
32
34
36
TEMPERATURE
25
30
35
40
45
45
45
45
50
55
60
65
70
75
75
75
75
80
85
What is the melting
Temperature?
How many minutes does
this take to melt?
What is the boiling
point?
Stop
***Equilibrium***
Equilibrium: two opposing changes occur at equal rates
Closed system: Matter can not enter or leave.
“ but energy can”
example: sunlight, heat from a burner, cooling by ice.
Equilibrium equations:
Whenever a liquid changes into a vapor it absorbs heat energy.
liquid + heat energy
vapor
Whenever a vapor condenses, it gives off heat energy
vapor
liquid + heat energy
Whenever a liquid , vapor reaches equilibrium
liquid + heat energy
vapor
Le Chatelier’s principle: When a system is at equilibrium
and is disturbed by a stress it attains a new equilibrium that
minimizes the stress.
Stress is typically: temperature, concentration, pressure.
Need to know: 2nd Law of Thermodynamics
Heat always travel from higher temp to lower temp.
“ same with energy, voltage, concentration, pressure, etc…..everything”
endothermic: absorbing energy or heat
exothermic: releasing energy or heat
liquid + heat
vapor
Equilibrium and temperature p.374
Add extra heat…….shift toward vapor …. endothermic reaction
Subtract heat (cool with ice) …shift toward liquid ….. exothermic reaction
Equilibrium and Concentration p.375
Add extra liquid ….. Shift toward vapor
Add extra vapor …. Shift toward liquid
Equilibrium and Pressure p.376
Pressure exerted by a vapor with its corresponding liquid
is called equilibrium vapor pressure
Add heat …increase vapor
which increases pressure vapor onto liquid.
Subtract heat…decrease vapor
which decreases pressure of vapor onto liquid.
“ think of your pepsi-cola drinks” easier to keep carbonated when cold”