Review Chapter 6:
Oxidation & Reduction
Reactions
Chemistry: The Molecular Nature of Matter,
6th edition
By Jesperson, Brady, & Hyslop
Chapter 7 Concepts
 Be familiar with Potential and Kinetic Energy
 Potential Energy changes as bonds break and form
 Average KE is proportional to Temperature
 Conservation of Energy
 Define system vs surroundings
 Track direction of heat transfer between system and surroundings
 Heat capacity calculations
 Specific heat calculations
 Exothermic vs Endothermic
 Heats of reactions:
 Calorimetry problems, qv vs qp
 First Law of Thermodynamics
 Define Enthalpy
 Enthalpy calculations:
 Hess’s law
 ΔHf ΔHrxn
2
Memorize
Total = Potential +
Energy
Energy
Kinetic
Energy
E = Efinal – Einitial
T (K) Avg KE = ½ mvavg2
A calorie (cal)
Energy needed to raise the temperature of 1 g
H2O by 1 °C
1 cal = 4.184 J (exactly)
1 kcal = 1000 cal
1 kg  m2
1 kcal = 4.184 kJ
1J
1 Cal = 1000 cal = 1 kcal
s2
1 kcal = 4.184 kJ
H°reaction =
Sum of all H°f of
all of the products
q = C × t
q = s  m  t
Work = –P × V
E = q + w
H = E + PV
–
Sum of all H°f of all
of the reactants
Endothermic & Exothermic
Surroundings
PE
heat
System
PE
increases
as bonds
break
ENDOTHERMIC
Heat + Reactants  Products
Products have stronger bonds and therefore a
higher potential energy then Reactants.
Heat is absorbed by the system.
ΔE +
ΔH +
PE
decreases
as bonds
form
ENDOTHERMIC
Heat absorbed
Reactants
Heat released
Products
EXOTHERMIC
EXOTHERMIC
System
heat
Surroundings
Reactants  Products + heat
Products have weaker bonds and therefore a
lower potential energy then Reactants.
Heat is released by the system.
ΔE -
ΔH -
System & Surroundings
heat
qsystem = –qsurroundings
System
Surroundings
Constant
Volume
qv
ΔE
Constant
Pressure
qp
ΔH
Open system
Closed system
Hess’s Law
Hess’s Law of Heat Summation
• Going from reactants to products
• Enthalpy change is same whether reaction takes
place in one step or many
Reactants
Path 2
step b
Path 1
Products
Path 2
step b
Sum of Enthalpies from
steps in path 2
=
Path 1 Enthalpy
Manipulating Thermochemical Rxns
aA (state) + bB (state)  cC (state) + dD (state)
1.
2.
3.
ΔH
When equation is reversed, sign of H°rxn must also be
reversed.
If all coefficients of equation are multiplied or divided by
same factor, value of H°rxn must likewise be multiplied or
divided by that factor
Formulas canceled from both sides of equation must be
for substance in same physical states
Strategy for Adding Thermochemical Rxns
1.
2.
3.
4.
Choose most complex compound in equation for one-step path
Choose equation in multi-step path that contains that compound
Write equation down so that compound
 is on appropriate side of equation
 has appropriate coefficient for our reaction
Repeat steps 1 – 3 for next most complex compound, etc.
5.
Choose equation that allows you to

cancel intermediates

multiply by appropriate coefficient
6.
Add reactions together and cancel like terms
7.
Add energies together, modifying enthalpy values in same way
equation modified

If reversed equation, change sign on enthalpy

If doubled equation, double energy