ENERGY
 The ability to do work or produce heat.
 It exists in two basic forms, potential energy and kinetic
energy:
 Potential: energy due to the composition or position of an
object
 Kinetic: energy of motion
 Chemical potential energy is the energy stored in a
substance because of its composition.
ENERGY FLOW
Exothermic: when heat flows from the object to its
surroundings; heat is released
Endothermic: when heat flows from the surroundings to
the object; heat is absorbed
Is making ice cream exothermic or endothermic?
LAW OF CONSERVATION OF ENERGY
In any chemical reaction or physical process, energy can
be converted from one form to another, but is neither
created nor destroyed.
HEAT (Q)
Energy that is in the process of flowing from a warmer
object to a cooler object.
The amount of heat required to raise one gram of water
by one degree Celsius is defined as a calorie (cal).
 1 Calorie = 1 kcal = 1000 cal
The SI unit of heat and energy is the joule (J).
CONVERTING ENERGY UNITS
1 J = 0.2390 cal
1 cal = 4.184 J
A granola bar contains 142 Calories. Convert this to
joules.
SPECIFIC HEAT
The amount of heat required to raise the temperature of
one gram of that substance by one degree Celsius.
q = m · c · ΔT
 q = the heat absorbed or released
 m = the mass of the sample in g
 c = the specific heat of the substance
 ΔT = the change in temperature
CALCULATIONS WITH SPECIFIC HEAT
The temperature of a sample of iron with a mass of
10.0g changed from 50.4˚C to 25.0˚C with the release
of 114J heat. What is the specific heat of iron?
If the temperature of 34.4g of ethanol increases from
25.0˚C to 78.8˚C, how much heat has been absorbed
by the ethanol? The specific heat of ethanol is
2.44J/(g·˚C)
MEASURING HEAT
A calorimeter is an insulated device used for measuring the amount of heat absorbed
or released during a chemical or physical process.
BOMB CALORIMETER
THERMOCHEMISTRY
The study of heat changes that accompanies chemical
reactions and phase changes.
System: the specific part of the universe that is being
studied (chemical reaction)
Surroundings: everything else
Universe = system + surroundings
ENTHALPY (H)
The heat content of a system at constant pressure
Enthalpy of reaction(ΔHrxn) is the change in enthalpy for a
reaction
ΔHrxn= Hfinal – Hinitial
ΔHrxn= Hproducts - Hreactants
If ΔH is positive, the reaction is endothermic
If ΔH is negative, the reaction is exothermic
THINK-PAIR-SHARE
Compare energy changes in chemical reactions to profits
and losses in a business.
 Each month the business has receipts (positive dollar
amounts) and expenses (negative dollar amounts).
 If the total receipts exceed expenditures, a positive
dollar amount or profit occurs.
 If expenditures are greater than receipts, money is lost
and a negative dollar amount results.
PRACTICE PROBLEM
A 75.0g sample of a metal is placed in boiling water until its
temperature is 100.0˚C. A calorimeter contains 100.00g of
water at a temperature of 24.4˚C. The metal sample is
removed from the boiling water and immediately placed in
the water in the calorimeter. The final temperature of the
metal and water in the calorimeter is 34.9˚C. Assuming
that the calorimeter provides perfect insulation, what is the
specific heat of the metal?
THERMOCHEMICAL EQUATION
A balanced equation that includes the physical states and energy change.
Example:
4Fe(s) + 3O2(g) → 2Fe2O3(s) ΔH= -1625 kJ
ENTHALPY (HEAT) OF COMBUSTION (ΔHCOMB)
The enthalpy change for the complete burning of one mole of a substance
Example:
C6H12O6(s) + 6O2(g) → 6CO2(g) + 6H2O(l) ΔHcomb=-2808kJ
CHANGES OF STATE
Molar enthalpy (heat) of vaporization (ΔHvap)
 H2O(l) → H2O(g) ΔHvap= 40.7kJ
 H2O(g) → H2O(l) ΔHcond= -40.7kJ
Molar enthalpy (heat) of fusion (ΔHfus)
 H2O(s) → H2O(l) ΔHfus= 6.01kJ
 H2O(l) → H2O(s) ΔHsolid= -6.01kJ
What would be the molar enthalpy of sublimation?
PRACTICE PROBLEMS
Calculate the heat required to melt 25.7 g of solid methanol at its melting point.
ΔHfus=3.22 kJ/mol
How much heat is evolved when 275 g of ammonia gas condenses to a
liquid at its boiling point? ΔHvap=23.3 kJ/mol
What mass of methane must be burned in order to liberate 12,880 kJ of
heat? ΔHcomb=-891 kJ/mol
PROBLEM-SOLVING LAB
Pg. 531
Make, Explain and Use the Graph
Brady and Antonio Rule!!!!!!!
HESS’S LAW
Read section on p. 534 and 535
Add the following equations:
A+B→C
C+D→E+B
EXAMPLE
Ex) 2S(s) + 3O2(g) → 2SO3(g) ΔH= ?
S(s) + O2(g) → SO2(g) ΔH= -297kJ
2SO3(g) → 2SO2(g) + O2(g) ΔH= 198kJ
EXAMPLE
 Use reactions a and b to determine ∆H for the following reaction.
 2CO + 2NO → 2CO2 + N2 ∆H = ?
 A) 2CO + O2 → 2CO2 ∆H = -566.0 kJ
 B) N2 + O2 → 2NO ∆H = 180.6 kJ
 4Al + 3MnO2 → 2Al2O3 + 3Mn ∆H = ?
 4Al + 3O2 → 2Al2O3 ∆H = -3352 kJ
 Mn + O2 → MnO2 ∆H = -521 kJ
SPONTANEOUS PROCESS
A spontaneous process is a physical or chemical change that occurs
with no outside intervention.
 Ex. Iron forming rust, combustion of methane, melting of ice cream
A non-spontaneous change is a change that occurs only when driven
e.g. forcing electric current through a metal block to heat it
What makes a reaction spontaneous?
WHAT DETERMINES IF A REACTION IS
SPONTANEOUS?
Entropy: Measure of the disorder or randomness of the particles
that make up a system.
 Spontaneous processes always proceed in such a way that the
entropy of the universe increases. (ΔS)
ΔSuniverse= ΔSsystem + ΔSsurroundings
 Larger entropy value, larger degree of randomness.
Law of Disorder (second law of thermodynamics): Spontaneous
processes always proceed in such a way that the entropy of the
universe increases.
LAW OF DISORDER (SECOND LAW OF
THERMODYNAMICS)
Law of disorder: Spontaneous processes always proceed in such
a way that the entropy of the universe increases.
 Entropy gas > entropy liquid > entropy solid
 Dissolving of a gas in a solvent always results in a
decrease in entropy
 An increase in temperature results in an increase in
entropy.
 Entropy increases when the number of product particles
is greater than the number of reactant particles.
 2SO3 (g) 2SO2 (g) + O2 (g) ΔSsystem > 0
ENTROPY, THE UNIVERSE AND FREE ENERGY
For any spontaneous reaction
 ΔSuniverse > 0
 ΔSuniverse is positive when,
 1. the reaction is exothermic
 2. The entropy of the system increases, so ΔSsystem is positive
Gibbs Free Energy (G) or Free energy:
-the energy that is available to do work.
ΔGsystem= ΔHsystem -TΔSsystem
Type of reaction or
process
ΔGsystem
ΔSuniverse
Spontaneous
Negative
Positive
Nonspontaneous
Positive
negative
How ΔHsystem and ΔSsystem Affect Reaction Spontaneity
-ΔHsystem
+ΔHsystem
+ΔSsystem
Always spontaneous
Spontaneity depends
upon temperature
-ΔSsystem
Spontaneity depends
upon temperature
Never spontaneous
PRACTICE PROBLEM
For a process, ΔHsystem=
145 kJ and ΔSsystem=322
J/K. Is the process spontaneous at 382 K?