Lecture 5 – Reaction Rates and Chemical Equilibrium & Acids
and Bases
1 – Reaction Rates and Chemical Equilibrium
Rates of reactions
Chemical kinetics is the study of reaction rates, how reaction rates change under varying
conditions, and what molecular events occur during the overall reaction.
For a reaction to take place, the molecules of the reactants must come into contact.
Collision theory => a reaction takes place only when molecules collide with the proper
orientation and sufficient energy. Many collisions can happen, but only a few lead to the
formation of a product.
Activation energy
Even when the collision has the proper orientation, sufficient energy is needed to break the
bonds between the atoms of the reactants.
Activation energy = the minimum amount of energy required to break the bonds between
atoms of the reactants
,A collision must provide enough energy to
push the reactants to the top of the energy
hill. Then the reactants may be converted to
products.
Reaction rates
The rate of reaction is determined by measuring the amount of a reactant used up OR the
amount of a product formed in a certain period of time
Pizza: You want to determine the rate at which pizza is eaten.
Assume 4 slices are eaten every 8 minutes. That gives a rate of 0.5 slices per minute.
After 16 minutes, all 8 slices are gone
,Factors that affect the rate of a reaction
All reactions are affected by changes in temperature, changes in the concentration of
reactants, and by the addition of catalysts
TEMPERATURE
At higher temperatures → reactant molecules have more kinetic energy → they move faster
→ they collide more often and with a greater energy
If you want your food to cook faster, you can increase the heat
CONCENTRATION OF REACTANTS
Concentration of the reactants increases → rate of the reaction increases
If there are more reacting molecules, more collisions that form products can
occur, and the reaction goes faster
Struggle with breathing? Then you’re given more oxygen, because
this increases the number of O molecules, and that increases the rate
at which oxygen combines with haemoglobin
CATALYSTS
A catalyst speeds up a reaction by lowering the energy of activation (= minimum energy
needed to break apart the bonds of the reacting molecules).
When the activation level is lowered, more collisions provide sufficient energy for reactants
to form a product.
A catalyst is a substance that increases
the rate of a chemical reaction without
itself undergoing any permanent
chemical change
A catalyst modifies the mechanism of the
reaction, but NEVER changes the
equilibrium state
, Chemical equilibrium
Forward reaction = all reactants are converted into products
But most often, reactants are not completely converted to products because of a reverse
reaction taking place where products collide to form the reactants.
When a reaction goes in both forward and reverse directions, it is reversible.
Going to the grocery store (you always come back); melting and freezing; money in
the bank, and out
Reversible chemical reactions
A reversible reaction proceeds in both the forward and reverse directions.
So, there are two reaction rates: one rate for the forward reaction and one rate for the
reverse reaction.
When molecules begin to react, the rate of the forward reaction is faster.
As reactants are consumed and products accumulate, the rate of the
forward reaction decreases, and the rate of the reverse reaction
increases
and Bases
1 – Reaction Rates and Chemical Equilibrium
Rates of reactions
Chemical kinetics is the study of reaction rates, how reaction rates change under varying
conditions, and what molecular events occur during the overall reaction.
For a reaction to take place, the molecules of the reactants must come into contact.
Collision theory => a reaction takes place only when molecules collide with the proper
orientation and sufficient energy. Many collisions can happen, but only a few lead to the
formation of a product.
Activation energy
Even when the collision has the proper orientation, sufficient energy is needed to break the
bonds between the atoms of the reactants.
Activation energy = the minimum amount of energy required to break the bonds between
atoms of the reactants
,A collision must provide enough energy to
push the reactants to the top of the energy
hill. Then the reactants may be converted to
products.
Reaction rates
The rate of reaction is determined by measuring the amount of a reactant used up OR the
amount of a product formed in a certain period of time
Pizza: You want to determine the rate at which pizza is eaten.
Assume 4 slices are eaten every 8 minutes. That gives a rate of 0.5 slices per minute.
After 16 minutes, all 8 slices are gone
,Factors that affect the rate of a reaction
All reactions are affected by changes in temperature, changes in the concentration of
reactants, and by the addition of catalysts
TEMPERATURE
At higher temperatures → reactant molecules have more kinetic energy → they move faster
→ they collide more often and with a greater energy
If you want your food to cook faster, you can increase the heat
CONCENTRATION OF REACTANTS
Concentration of the reactants increases → rate of the reaction increases
If there are more reacting molecules, more collisions that form products can
occur, and the reaction goes faster
Struggle with breathing? Then you’re given more oxygen, because
this increases the number of O molecules, and that increases the rate
at which oxygen combines with haemoglobin
CATALYSTS
A catalyst speeds up a reaction by lowering the energy of activation (= minimum energy
needed to break apart the bonds of the reacting molecules).
When the activation level is lowered, more collisions provide sufficient energy for reactants
to form a product.
A catalyst is a substance that increases
the rate of a chemical reaction without
itself undergoing any permanent
chemical change
A catalyst modifies the mechanism of the
reaction, but NEVER changes the
equilibrium state
, Chemical equilibrium
Forward reaction = all reactants are converted into products
But most often, reactants are not completely converted to products because of a reverse
reaction taking place where products collide to form the reactants.
When a reaction goes in both forward and reverse directions, it is reversible.
Going to the grocery store (you always come back); melting and freezing; money in
the bank, and out
Reversible chemical reactions
A reversible reaction proceeds in both the forward and reverse directions.
So, there are two reaction rates: one rate for the forward reaction and one rate for the
reverse reaction.
When molecules begin to react, the rate of the forward reaction is faster.
As reactants are consumed and products accumulate, the rate of the
forward reaction decreases, and the rate of the reverse reaction
increases
