Transcript Factors that Affect the Rate of Reaction. Alfred Nobel amassed a fortune during his lifetime from his 355 inventions, dynamite is the most famous. In.

Factors that Affect the Rate of Reaction.
Alfred Nobel
amassed a fortune during
his lifetime from his 355 inventions,
dynamite is the most famous.
In 1888, opened a newspaper to read his own
obituary. As it was Alfred's brother Ludvig
who had died, the obituary was eight years
premature. Nobel s reflection on his life’s
impacts inspired him to leave his fortune to
create prizes for the"greatest benefit on
mankind" in physics, chemistry, peace,
physiology or medicine, and literature.
Nobel's instructions named a Norwegian
Nobel Committee to award the Peace Prize.
Now, Norway's Nobel Committee was
responsible for awarding the Nobel Peace
Prize and the Swedish institutions retained
responsibility for the other prizes.
nitroglycerin
Table salt is an ionic compound
transfer electrons from the metal to the non-metal to
form an easily dissociated compound (just add water)
◦ Sodium chloride, NaCl (s), is a comprising sodium ions,
Na+, and chloride ions, Cl–.
◦ Cation (+) and anion (-) attract like magnets
3
Free energy (if you get energy or put it in) can be used to
predict whether a process is spontaneous (favorable) or
nonspontaneous (not favorable)
Which one
would you
favor?
ΔG < 0
spontaneous
ΔG > 0
nonspontaneous
4
The
same principles can be applied to chemical
reactions to predict whether they are favorable or
not:
Α → B
Α → B
A
Free
Energy
ΔG > 0
ΔG < 0
spontaneous
(G)
Free
Energy
nonspontaneous
(G)
Β
Progress of
reaction
A
Progress of
reaction
5
Β
Just
because a reaction
is spontaneous, does not
mean that it will occur at
an observable rate.
Why can Beer’s
say diamonds
are forever?
Diamond and graphite are
two different forms of pure
carbon.
The reaction that converts
diamond to graphite is
actually a favorable one
Diamond → Graphite
Diamond
Free
Energy
ΔG < 0
spontaneous
(G)
Graphite
Progress of
reaction
6
There
is is a hill that for most reactions the reactants
must climb and go over to before they can go on to
become product.
Α → B
Free
Energy
A
(G)
Reactants
Products
Β
Progress of
reaction
7
The amount of energy you need to put is the
activation energy, Eact.
◦ The activation energy has no effect on the overall change
in the free energy for the reaction.
Energy you
put-in
Α → B
Free
Energy
(G)
Eact > 0
A
Reactants
ΔG < 0
Β
spontaneous
Products
Progress of
reaction
8
Energy you
get (gain)
So before we go calling DeBeers can you think of an
anwers to why the reaction that converts diamond to
graphite is actually a favorable one – but it doesn’t
happen often (or quickly)
Α → B
Free
Energy
(G)
Eact > 0
A
Reactants
ΔG < 0
Β
spontaneous
Products
Progress of
reaction
10
The
activation energy for the conversion of
diamond to graphite is very, very,very high.
Diamond → Graphite
Free
Energy
(G)
Eact > 0
Diamond
ΔG < 0
Graphite
spontaneous
Progress of
reaction
11
The
reaction rate (speed) of a reaction is
determined by the height of the hill.
◦ The higher the activation energy, the slower the reaction
rate.
But WHY, How is this connected to the Nature of the
reactants?
What takes energy to make and break?
12
We can estimate by: Counting the number of bonds
being broken and made
5C2O42- + 2MnO4- + 16H+ → 10CO2 + 2Mn2+ + 8H2O
Many bonds need to be broken and made =slow reaction.
Fe2+ + Ce4+ → Fe3+ + Ce3+
This is a fast reaction because no bonds are being
broken
( only 1 electron is being transferred)
Reactants with strong bonds = more Ea=slower reaction rate
Reactants with weak bonds =smaller Ea= faster reaction rate
13
We know two ways to speed up the reaction rate.
We just haven't thought about them as overcoming activation energies but now we
will.
◦ Increase the temperature of the reactant molecules.
• This increases the kinetic energy, which increases the motion of
the reactant molecules. This increases the frequency with which
they will collide with one another to react.
◦ Increase the concentration of the reactant molecules.
• This increases the number of reactant molecules. This also
increases the frequency with which they will collide with other
reactant molecules.
15
We
will dive into collision theory next class for now:
Increase the temperature of the reactant molecules.
• This increases the kinetic energy, which increases the motion
of the reactant molecules. This increases the frequency with
which they will collide with one another to react.
Increase the concentration of the reactant molecules.
• This increases the number of reactant molecules. This also
increases the frequency with which they will collide with other
reactant molecules.
16
There
is a third way to speed up the reaction rate
and that is to lower the height of the hill.
◦ This is done using catalysts, which provide an alternative
pathway over the hill for theΑ reactants.
→ B
Free
Energy
Eact > 0
without catalyst
with catalyst
A
(G)
ΔG < 0
Β
spontaneous
Progress of
reaction
17
Catalysts
speed up a reaction, by lowering the
activation energy but are not produced or consumed
in a reaction.
◦ In the reaction equation, their presence in indicated
above or below the reaction arrow.
They have not effect on the change in
free energy for the reaction, ΔG.
If the number
of bonds
broken/made
remains the
same how
might catalysts
do this?
They cannot be used to make an unfavorable reaction favorable.
18
In
biological systems, catalysts are called enzymes.
◦ Most enzymes are proteins.
◦ Nearly every reaction that takes place in a living cell has
an enzyme associated with.
◦ Enzymes bind the reactants, facilitate the reaction, and
then release the products.
We will revisit ENZYMES over and
over and over again!
They are fascinating!
ENZYMES can do what chemical
factories do with little /no effort!
Remember the Harper-Borsh
process for ammonia.
19