Kinetics/ Equilibrium

Question 1

Law of relative rates

Answer 1

A way to determine the rate of a reaction by using appearance or disappearance of reactants or products during the course of a reaction.

( stoichiometric coefficient) x (( change in reactant or product)/ ( change in time)) = rate

• Positive or negative sign applied to equation depending on whether the reactant or products is getting consumed or produced*

Question 2

What are the 4 factors that effect the rate of a reaction?

Answer 2

• Medium - conditions where reaction is taking place.
• Temperature- increase temperature increases rate constant.
• Concentrations of reactants- more reactants increase rate due to more collisions happening.
• Catalysts- substances that decrease the activation barrier and therefore increases the reaction rate. Increases rate constant.

Question 3

Rate laws

Answer 3

Laws that describes the rate of a SPECIFIC reaction. In the form of:

Rate = K [A]^m [B]^y

• M and Y are reaction orders and represent the effect reactant concentrations has on the reaction rate. Overall reaction order is the sum of these values.

Question 4

Method of initial rates

Answer 4

Method to determine the rate from experimental data.
Steps:
1. Pick trial where one reactant is changing and the other is constant.
2. divide the reactant concentration picked and the corresponding rates.
3. Plug values into following equation and solve for the reaction order ( Rate= [A]^y
4. Repeat to find the other reaction order.
5. Choose any trial and plug in values to find the rate constant, K.

Question 5

Collision theory

Answer 5

States how reactions progress and states that reactants must collide in the correct orientation and with the right speed to form the activated complex ( transition state) which is a state of high energy.

Question 6

Activation Energy ( Ea)

Answer 6

Amount of energy reactants must overcome to become products or the reverse.
- If the K.E. of the reactants is less the the Ea the reaction proceeds slowly.
- If the K.E. of the reactants is more than the Ea the reaction proceeds quickly.

Question 7

Arrhenius Equation

Answer 7

Equation that mathematically represents collision theory.

Question 8

Reaction Mechanisms

Answer 8

They show each of the individual steps of a reaction.
- Intermediates are compounds that are made and quickly used and so they cancel.
- Each step of the mechanism is an elementary reaction.

Question 9

How to determine the reaction orders?

Answer 9

For elementary reactions it’s their stoichiometric coefficients. For non- elementary reactions it must be determined experimentally ( initial rates method).

Question 10

Zero- order reaction

Answer 10

Reaction rate depends not on reactant concentrations only on the rate constant which can only be changed by changing the temperature or adding an catalyst.

Question 11

1st order reaction

Answer 11

Rate is proportional to the change of one reactant.
Rate = K [A]

Question 12

2nd order reaction

Answer 12

The rate is proportional to the change in concentrations of either two reactants with 1 orders or one reactant with second order.

Question 13

How to determine order reaction graphs?

Answer 13

By determining the overall reaction orders.

Question 14

Mixed order

Answer 14

Reaction happens over the course of a reaction

Question 15

Broken order

Answer 15

reaction order is a fraction.

Question 16

When is a reaction at equilibrium?

Answer 16

When the rate of the forward reaction is equal to the rate of the reverse reaction. Therefore the concentrations of the reactants and the products remain constants during equilibrium ( not equal).

Question 17

Reaction quotient

Answer 17

(Qc) Tells us the extent by which the reaction is towards equilibrium.

If Qc< Kc, rxn moves in forward direction towards equilibrium.

If Qc > Kc, rxn moves in the reverse direction to reach equilibrium.

If Qc= Kc, reaction is in equilibrium.

Question 18

What happens when the equilibrium constant is greater than one? Less then one?

Answer 18

There are more products than reactants at equilibrium.

More reactants than products at equilibrium when Kc is less than one.

Question 19

What states must be excluded from the equilibrium expression?

Answer 19

Pure solids and liquids.

Question 20

How can you change Kc?

Answer 20

By changing the temperature or adding a catalyst

Question 21

Larger the Kc…
Smaller the Kc…

Answer 21

Larger the Kc = more towards the products the equilibrium lye
Smaller the Kc = more towards the reactants the equilibrium lye.

Question 22

What’s the equilibrium constant for the other direction if it’s Kc for one direction?

Answer 22

The inverse of the Kc ( 1/Kc).

Question 23

Why are solids, liquids, and solvents not in the equilibrium expression?

Answer 23

No, they’re emitted because their concentration is much greater and so is constant.