Studied by 2 people
Do all things have the same reaction rate?
No, they are varied
Activation Energy
The minimum amount of energy needed to convert the colliding molecules into products
What are the conditions for a reaction to occur?
Collision: Reactants must collide
Orientation: The reactants must align properly (side-by-side) to break and form bonds
Energy: The collision provides sufficient energy for activation
Is proper orientation all that is needed to form products?
No, even when a collision has the proper orientation there still must be sufficient energy to break the bonds between the atom of the reactants
Rate of Reaction
The rate or speed of a reaction
What is the Rate of Reaction calculated by?
Reactant used up in a certain period of time
OR
Product formed in a certain period of time
What is the formula for Rate of Reaction?
Change in concentration of reactant or product/change in time
What factors affect the Rate of Reaction?
Any reaction
Temperature changes
Changes in reactant concentration
Adding a catalyst
Surface area (needed for a lab we’ll do)
Rate of Reaction: Temperature
At higher temperatures, the increase in kinetic energy causes reactant molecules to
Move faster
Collide more
Collide with more energy
What is the rate of change in Rate of Reaction: Temperature?
For every 10° increase, most reaction rates approximately double
Rate of Reaction: Reactant Concentration
When there are more reacting molecules, more collisions that form products can occur and the reaction goes faster
More opportunities for collisions
Rate of Reaction: Catalysts
Adding a catalyst speeds up the rate of reaction by providing an alternate pathway that has a lower activation energy
When activation energy is lowered, more collisions provide sufficient energy for reactants to form products
During reactions, do catalysts get changed or consumed?
No, they do not
Reversible Reactions
When a reaction proceeds in both a forward and reverse direction
Both the forward and reverse directions occur at the same time
Do reversible reactions have the same rate at equilibrium?
Yes
Before equilibrium, however, they have two rates
Do reversible reactions have the same concentrations at equilibrium?
No, not necessarily
Rate of reversible reactions
As the reaction progresses, the rate of the forward reaction decreases and the rate of the reverse reaction increases.
At equilibrium, the rates of the forward and reverse reactions are equal
Concentration of reversible reactions
Equillibrium
Equilibrium is reached when there are no further changes in the concentrations of the reactant and products
When is a reversible reaction at equilibrium?
The rate of the forward reaction is equal to the rate of the reverse reaction
The forward and reverse reactions continue at the same rate
Equilibrium Expression
Multiplies the products together and divides by the concentration of the reactants. Also raises the concentration (moles/L) of each species to a power that is equal to its coefficient in the balanced chemical equation
Equilibrium Constant
Kc, a numerical value obtained by substituting experimentally measured molar concentrations at equilibrium into the expression
What is equilibrium expression
Kc = [C]^c x [D]^d/[A]^a x [B]^b
What phases work with equilibrium expressions and which do not?
Gas and Aqueous WORK
Liquid and Solid DO NOT WORK
What do the brackets mean in an equilibrium expression?
Moles per liter
When will Kc stay the same?
For the same chemical reaction
When the temperature stays constant
What is the unit for Kc
There are none
What can the values of Kc be? What causes them?
They can be large or small depending on whether equilibrium is reached with
More product than reactant
OR
More reactant than product
Small Kc Value
Little reaction occurred
Low concentration of product, higher concentration of reactants
Produced from the reverse reaction
Large Kc Value
Reaction essentially complete
Low concentration of reactants, higher concentration of products
Produced from the forward reaction
Kc Value ≈ 1
Reactants and products are in a similar concentration
What happens when conditions of a reaction at equilibrium are changed?
The forward and reverse reactions will no longer be equal
Le Châtelier’s Principle
When stress is placed on a reaction at equilibrium, the system responds by changing the rate of the forward or reverse reaction in the direction that relieves the stress.
Tries to become equal again
What items are considered to be stress on equilibrium? What isn’t?
Concentration
Volume/Pressure (They’re related = Boyle’s Law)
Temperature
NOT catalysts
Stress on Equilibrium: Adding Reactant
The rate of the forward reaction increase to form more product until the system is again at equilibrium
Shifts toward the products
Stress on Equilibrium: Removing Reactant
The rate of the reverse reaction increase to form more reactant until the system is again at equilibrium
Shifts toward the reactants
In A + B ⇌ C + D, what would these shift to?
↑D
↓C
↑A
↓B
↑D = reactants
↓C = products
↑A = products
↓B = reactants
When determining what will happen when changing volume changes on equilibrium, what must you always do?
Count the moles
What will occur if you change the volume at equilibrium?
The concentration of gasses in the mixture will change
Stress on Equilibrium: Decrease Volume
Decreasing the volume increases the concentration of gasses, and the system shifts in the direction of the smaller number of moles to compensate
Stress on Equilibrium: Increase Volume
Increasing the volume decreases the concentration of gasses, and the system shifts in the direction of the larger number of moles to compensate
Stress on Equilibrium: Pressure
Increase and Decrease
Think of it like volume and do the opposite :D
Yes, I’m too lazy to write it but anyway
In A(g) + B(g) ⇌ C(g), where does the reaction shift?
Decrease Pressure
Increase Pressure
Increase Volume
Decrease Volume
Decrease Pressure = reactants
Increase Pressure = products
Increase Volume = reactants
Decrease Volume = products
Where is the heat in an endothermic reaction vs an exothermic reaction?
In the equation
Endothermic: Reactant Side
Exothermic: Product Side
Stress on Equilibrium: Decreasing Temperature
Exothermic
Causes the system to respond by shifting the reaction toward more heat
Shifts toward products, increasing heat in the system
Stress on Equilibrium: Increasing Temperature
Exothermic
Causes the system to respond by shifting the reaction toward removing heat
Shifts toward reactants, decreasing heat in the system
Stress on Equilibrium: Decreasing Temperature
Endothermic
Causes the system to respond by shifting the reaction toward more heat
Shifts toward reactants, increasing heat in the system
Stress on Equilibrium: Increasing Temperature
Endothermic
Causes the system to respond by shifting the reaction toward removing heat
Shifts toward products, using up the heat
Note 
Flashcard (31)