Transcript Chapter 11 Notes Thermochemistry: Investigates heat changes that

Good Morning 4/8/2016
• Today we will be working on the
notes for ch 11.
Chapter 11 Notes
Thermochemistry: Investigates
heat changes that occur during
chemical reactions.
Energy:
• The ability to do work. Measured
in Joules (J) or calories (cal)
Work:
• Force applied over distance. (W =
F x d) work is also measured in
joules
Chemical Potential Energy:
• Energy that is given off when
chemical bonds are formed.
Heat: Energy that is transferred
from one substance to another.
• Represented by a “q” or “H” in an
equation.
Heat is measured in Joules (J) or
calories (cal.), the same units as
energy.
Heat flows from hot objects to cold
objects.
Only changes in heat can be
detected.
Law of Conservation of Energy:
• In any chemical or physical
process, energy is neither created
nor destroyed.
Most energy that is considered
“lost” is usually just dispersed as
heat into its surroundings.
Exothermic:
• Energy is released to its
surroundings.
Represented by the word “energy”
in the products of a chemical
equation.
Heat flows out of the system.
(Heat change < 0)
Endothermic:
• Energy is absorbed from its
surroundings.
Represented by the word “energy”
in the reactants of a chemical
equation.
Heat flows into the system. (Heat
change > 0)
Heat Capacity:
• The amount of heat needed to raise
the temperature of an object
exactly 1.0 C
Specific Heat Capacity
(Also called “Specific Heat”)
The amount of energy needed to
raise the temperature of 1 gram of
the substance 1C.
Represented by the symbol “C” in
an equation.
Specific Heat Capacity Label = J/gC
Specific Heat Capacity Equation:
q = H = m x T x C
calorie:
• English unit for measuring heat
changes.
The amount of energy needed to
raise the temperature of 1 gram of
Water by 1C.
Calorie :
• Equal to 1000 calories or 1 kcal.
(Note the capital C)
This unit is general used to
measure the energy content in
food.
• It is what we mean when we talk
abou the number of Calories in
Food.
Joule:
• SI unit for measuring heat or
energy.
1 Joule = energy needed to lift 1 N
by 1 meter. 1 calorie = 4.184
Joules.
kg  m
J  N m  2
s
2
Calorimetry:
• The accurate and precise
measurement of heat changes for
chemical or physical processes.
Calorimeter:
• A device
used to
measure
the
absorption
or release
of heat in
chemical
or physical
reactions.
Enthalpy (H):
• The heat content of a system at
constant pressure.
Heat of Reaction: a.k.a. Enthalpy
Change (ΔH)
• The amount of heat absorbed or lost
by a system during a process at
constant temperature
ΔH = H products – Hreactants
ΔH is positive for an endothermic
reactions (energy is gained)
Heat content of products is greater
than the heat content of the
reactants
ΔH is negative for an exothermic
reactions (energy is lost)
Graphs
Heat of Combustion:
• The heat released during a
chemical reaction in which one
mole of a substance is completely
burned.
Molar Heat of Fusion (Hfus):
• The energy needed to melt 1 mole
of a substance.
Problem: The molar heat of fusion
of water is 6.009 kJ/mol. How much
energy is needed to convert 60
grams of ice at 0°C to liquid water at
0°C?
1 mol H2O
6.009 kJ
60g H2O x
x
= 20.00 kJ
18.02g H2O
1 mol H2O
Molar Heat of Solidification
(Hsolid):
• The heat lost when 1 mole of a
liquid solidifies.
Molar Heat of Vaporization
(Hvap):
• The amount of heat necessary to
vaporize 1 mole of a given liquid.
Molar Heat of Condensation
(Hcond):
• The amount of heat released when
1 mole of a gas vapor condenses.
Molar Heat of Solution (Hsoln):
• The heat change that results when
1 mole of a substance is dissolved
in water.
Hess’s Law of Heat Summation:
• If you add two or more
thermochemical equations to give
a final equation, then you can also
add the heats of reaction to give
the final heat of reaction.
Example:
Eq 1 A + B  D + C
H = -175 J
+
Eq 2
CA+E
H = 75 J
=
A + C + B  D + E + A + C H = -100 J
Writing Thermochemical
Equations
1. Fraction coefficients may be used
because coefficients represent mole
quantities, NOT atoms or molecules
2. Use appropriate state/phase
symbols (g) (l) (s)
3. ΔH is proportional to the number of
moles
4. ΔH is usually not influenced
significantly by the temperature of
the system