THERMODYNAMICS
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Units for Measuring Heat
The Joule is the SI system unit for measuring
2
heat:
1 kg  m
1 Joule  1 newton  meter 
2
s
The calorie is the heat required to raise the
temperature of 1 gram of water by 1 Celsius
degree
1 calorie  4 . 18 Joules
1 L atm = 101.3 J
Definitions #1
Energy: The capacity to do work or produce heat
Potential Energy: Energy due to position or
composition
Kinetic Energy: Energy due to the motion of the
object
KE 
1
2
mv
2
Definitions #2
Law of Conservation of Energy: Energy
can neither be created nor destroyed, but
can be converted between forms
The First Law of Thermodynamics: The
total energy content of the universe is
constant
State Functions depend ONLY on the
present state of the system
ENERGY IS A
STATE FUNCTION
A person standing at the
top of Mt. Everest has the
same potential energy
whether they got there by
hiking up, or by falling
down from a plane 
WORK IS NOT A
STATE FUNCTION
WHY NOT???
E = q + w
E = change in internal energy of a system
q = heat flowing into or out of the system
-q if energy is leaving to the surroundings
+q if energy is entering from the surroundings
w = work done by, or on, the system
-w if work is done by the system on the
surroundings
+w if work is done on the system by the
surroundings
Energy Change in Chemical Processes
Endothermic:
Reactions in which energy flows into the
system as the reaction proceeds.
+ qsystem
- qsurroundings
Energy Change in Chemical Processes
Exothermic:
Reactions in which energy flows out of the
system as the reaction proceeds.
- qsystem
+ qsurroundings
Work, Pressure, and Volume
w   PV
Expansion
+V (increase)
-w results
Esystem decreases
Work has been done
by the system on the
surroundings
Compression
-V (decrease)
+w results
Esystem increases
Work has been done
on the system by the
surroundings
Enthalpy
• H is a state function – ΔH doesn’t depend on
the pathway between the two states
H = E + PV,
E is internal energy of the system,
P is pressure of the system, and V is volume of
the system.
At constant pressure and knowing only P-V work is
allowed (w=-PΔV), we can derive:
-ΔH = q, at constant pressure
ΔH = Hρroducts - Hreactants
Example 6.4
• When 1 mole of methane is burned at constant pressure,
890 kJ of energy is released as heat. Calculate ∆H for a
process in which a 5.8 g sample of methane is burned at
constant pressure.
Given:
Find: ∆H of the rxn (KJ)
• Mass = 5.8 g CH₄
• Molar mass CH₄ = 16.04 g
• q of the product = ΔH = -890 kJ/mol CH₄
Find moles of methane:
5.8 g 1 mole = 0.36 mol
16.04g
∆H = .36 mol -890 kJ = -320 kJ, exothermic
1 mol
Calorimetry
The amount of heat absorbed or released during a
physical or chemical change can be measured,
usually by the change in temperature of a known
quantity of water in a calorimeter.
Specific Heat
The amount of heat required to raise the temperature
of one gram of substance by one degree Celsius.
Substance
Specific Heat (J/g·K)
Water (liquid)
4.18
Ethanol (liquid)
2.44
Water (solid)
2.06
Water (vapor)
1.87
Aluminum (solid)
0.897
Carbon (graphite,solid)
0.709
Iron (solid)
0.449
Copper (solid)
0.385
Mercury (liquid)
0.140
Lead (solid)
0.129
Gold (solid)
0.129
Catalyst (10 mins)
In book: P.277 #49
Calculations Involving Specific Heat
at constant pressure
q  s  m  T
q = Heat lost or gained
s = Specific Heat Capacity
T = Temperature change
Assumption: that the density of
the solution is the same as pure
water, 1 g/mL. Otherwise, a
different density will be given.
Example 1
• 1.00 x 10² mL of 0.500 M HCl was mixed with 100.
mL of 0.500 M NaOH in a constant pressure
calorimeter. Initially, both solutions are at 22.5˚C.
Find the heat change on a molar basis for the rxn.
NaOH(aq) + HCl(aq) -> NaCl(aq) + H₂O (l)
• Qcal (surrounding):
qrxn (∆H)(system):
100. mL HCl soln = 100g
.05 mols HCl
100 mL NaOH soln = 100 g
.05 mols NaOH
s = 4.18 J/g C
Ti: 22.50 ˚C
Tf: 25.86˚C
Example 2
• A 3.53 g sample of ammonium nitrate (NH₄NO₃) was
added to 80.0 mL of water in a coffee cup calorimeter.
The water temp decreased from 21.6 C to 18.1 C. Find
the ∆Hrxn for:
2NH₄NO₃(s) -> 2NH₄⁺(aq) + 2NO₃⁻(aq)
Qcal (surroundings)
∆Hrxn (system)
3.53 g NH₄NO₃
3.52 g NH₄NO₃
80.0 mL water = 80.0g
Total mass=83.5g
S= 4.18 J/g C
Ti= 21.6 ˚C
Tf= 18.1 ˚C
Classwork
• Do #54, then 53, which will be a little different
• Review sec 6.2 in packet, then work on 39, 41, 43, 49,
51, 57.
• Recommended reading: Calorimetry p.244-248, then
248-251