Kinetics Class #2
OB: mastering the art of the potential
energy diagram, and a few vocabulary
words to go with them
Chemical reactions occur when enough particles collide with sufficient energy
(but not too much) and these collisions occur with proper orientation of the
particles.
Any process that encourages more and stronger
collisions will decrease the time it takes for a
chemical reaction to happen, or more importantly,
they will increase the rate of the chemical reaction.
The rate
of a
Chemical
Reaction
=
1
time
Let’s draw the potential energy diagram for
sodium hydroxide dissolving into water
Potential
energy
kJ/mole
Time of the reaction…
First, write yourself the balanced thermochemical equation, and make
note of exo or endothermic…
NaOH(S)
Na+1(AQ) + OH-1(AQ) + energy ΔH = -44.51 kJ (exo)
sodium hydroxide dissolving into water
Potential
energy
kJ/mole
Time of the reaction…
Now we draw
NaOH(S)
Na+1(AQ) + OH-1(AQ) + energy ΔH = -44.51 kJ (exo)
sodium hydroxide dissolving into water
Potential
energy
kJ/mole
Time of the reaction…
Now we draw
NaOH(S)
Na+1(AQ) + OH-1(AQ) + energy ΔH = -44.51 kJ (exo)
sodium hydroxide dissolving into water
Potential
energy
reactants
kJ/mole
We don’t know
the actual
levels, but we
know that this
difference is
44.51 kJ/mole
AE
Represents the
activation
complex, the
transition
between R + P.
-ΔH
products
Time of the reaction…
Vocab x 5
Potential energy – the energy stored in the bonds
of the reactants or the products
Activation energy – the energy it takes to start a
chemical reaction. It must be sufficient or else.
Activation complex – the transitional state of
being, where reactants are coming apart but are
not yet products
ΔH – the difference between the potential energy of
the reactants and the potential energy of the products
Potential energy diagram – a graph showing the flow
of energy of a chemical reaction. Can be exo or
endothermic
Draw the potential energy diagram for the synthesis of aluminum oxide. Label
the reactants, products, AE, AC, ΔH (make it + or – as needed), and
put labels on the graph, and a title too. Go!
Draw the potential energy diagram for the synthesis of aluminum oxide. Label
the reactants, products, AE, AC, ΔH (make it + or – as needed), and
put labels on the graph, and a title too. Go!
PE diagram for synthesis of aluminum oxide
ΔH = -3351 kJ/mole
AC
Al + O2
PE
kJ/mole
AE
-ΔH
Al2O3
Time of the reaction
In an endothermic reaction, energy is absorbed, the products have more energy
in them than the reactants had. Where does this energy come from?
(the environment – which is why these reactions feel cold. They “steal” energy
from the immediate surroundings, bringing into the bonds of the reaction.
We will attempt to draw the PE diagram for the dissolving of sodium chloride into
water NaCl
Na+1 + Cl-1 + energy
ΔH = +3.88 kJ/mole
Go!
Table salt dissolves in water, ΔH = +3.88 kJ/mole
PE
kJ/mole
Time of reaction
Table salt dissolves in water, ΔH = +3.88 kJ/mole
PE
kJ/mole
Time of reaction
13
Table salt dissolves in water, ΔH = +3.88 kJ/mole
Ions in solution
PE
kJ/mole
salt
Time of reaction
AE
+ΔH
Draw the PE diagram for the combustion of propane.
Indicate the PE of reactants, products, AE, AC, ΔH, and a title.
title
Y axis
label
X axis label
Draw the PE diagram for the combustion of propane.
Indicate the PE of reactants, products, AE, AC, ΔH, and a title.
The combustion of propane ΔH = -2219.2 kJ/mole
PE
kJ/mole
C3H8 + O2
AE
-ΔH
CO2 + H2O
Reaction time
NOTE: the PE of the products is less than the PE of the reactants.
Where is the missing energy? Matter, nor energy, can be created or
destroyed in any chemical reaction, or physical change.
Let’s look over the celebration for solutions and water now.
Homework tonight…
Kinetics HW #2