# Lecture 14 ```Lon-Capa
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4th HW assignment due Friday, 10/10, 5 pm.
It is open now.
3rd Quiz due Sunday, 10/12 by 10 pm. It
will open Friday, 10/10 at 5 pm.
5th HW assignment is also open!
1
Bomb Calorimeter
2
Hess’s Law
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Due to first law and H being a state function.
If a reaction is reversed, the sign of H is also
reversed
The magnitude of ΔH is directly proportional to
the quantities of reactants and products in a
reaction.
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That is, if the coefficients in a balanced equation are
multiplied by an integer, the value of H is multiplied
by the same integer.
3
Clicker Question
Given the following data
2NH3(g)  N2(g) + 3H2(g)
2H2(g) + O2(g)  2H2O(g)
H = 92kJ
H = -484kJ
Determine ΔH for
2N2(g) + 6H2O(g)  3O2(g) + 4NH3(g)
a)
b)
c)
d)
e)
-1268 kJ
1268 kJ
1636 kJ
-1636 kJ
I did not/cannot get any of these answers.
4
Pathway for the Combustion of Methane
5
Schematic Diagram of Energy Changes
6
Chapter 9: Problem #99
When water is supercooled, it freezes at a
temperature below 0.0&deg;C. If 10.9 kJ of energy
as heat is released when 2.00 mol of
supercooled water at –15.0&deg;C freezes, calculate
the molar enthalpy of fusion for ice at 0.0&deg;C and
1 atm. Assume the molar heat capacities are
temperature independent.
[for H2O(l): 75.3J/Kmol, for H2O(s): 37.5J/Kmol]
7
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