2. Enthalpy Changes
a) What is "Enthalpy"?
i) enthalpy is the total PE and KE of a reaction
ii) think of enthalpy as heat of reaction or energy of reaction
iii) symbol for enthalpy is H.
symbol for change in enthalpy is H
b) How does enthalpy apply to rea
1. Activation Energy
a) Ineffective Collisions
Not all collisions between reactants will result in products. If they do not
collide with enough "activation energy" (i.e.: not head on collision or not fast
enough), then the reactants will not react!
10. Reaction Mechanisms
The reactants might not all combine at once, but in fact, take a sequence of steps to reach
the product. Each step can also proceed at its own rate!
5. Equilibrium Calculations
Type 1 (system at equilibrium)
What is the Keq for the reaction 2HI (g)
H2 (g) + I2 (g) if there is
2.0 mol of HI, 3.0 mol of I2, and 3.5 mol of H2 in a 5.0L closed flask?
[H2] = 3.5/5 = 0.7 M
Keq = [H2][I2]
[I2] = 3/5 =
11. Reaction Profiles
Lets include everything we have learned: exothermic/endothermic, enthalpy,
activation energy and intermediates!
Example 1: Building the house reaction
Ea 2nd step
Ea 1 step
Ea 3rd step
8. Le Chateliers Principle
This principle explains how equilibrium works in a nutshell!
If a reaction in equilibrium is subjected to a change, the equilibrium will take
steps to counteract that change.
Le Chateliers principle is a tool we can use to predi
4. Equilibrium Calculations contd
Type 3 (system changing to equilibrium Calculating concentration of a species)
Example 1: 2A (g) + B (g)
An unknown amount of C was placed into a 3.0 L flask. When equilibrium was
reached, the concentration of A wa
7. Equilibrium Systems in Solutions
a) Whats Different with Solutions?
i) solutions at equilibrium will follow all we learned about Le Chateliers principle
and gases from previous, but there is a bit more info required for dealing with
6. What Causes an Equilibrium?
A reaction will either: 1. proceed forward
2. not proceed (proceed in reverse)
3. form an equilibrium.
i) The side of the reaction having the least enthalpy is favored.
ii) In other words, the exothermic reaction
9. Quantitative Equilibrium
a) Equilibrium Expression
i) we can quantify (attach a numerical value) the equilibrium for most reactions by
creating a ratio of products to reactants.
A + B
3. Equilibrium Background
a) Reversible Reactions
i) Many reactions can go in reverse and have separate activation energies!
N2O4(g) is heated in a closed flask to form 2NO2(g) molecules
N2O4 + energy 2NO2
2NO2(g) molecules will then combine