2A Reaction Rate And Mechanisms

Question 1

Activation energy and rate of reaction relationship

Answer 1

The lower the activation energy/barrier, the rate of reaction will be higher

Question 2

1. Do reaction rates change with temperature
2. What is Arrhenius law
3. Explain each part

Answer 2

1. Yes, reaction rates generally change with temperature
2. K=A * e^(-Ea/RT)
3. Ea is Activation energy, R=8.314 J/K mol, T is absolute temperature, A is pre=exponential factor

Question 3

Very few reactions occur the way they are ____.

Answer 3

Written

Question 4

1. Elementary steps/Elementary reactions
2. Reaction mechanism
3. Rate determining (rate limiting)

Answer 4

1. The overall progress of a chemical reaction can be represented at the molecular level by a series of steps/reactions
2. The sequence of elementary steps that leads to product formation
3. The slowest step

Question 5

Intermediates (Definition, when is it formed, lifespan)

Answer 5

• Species that appear in a reaction mechanism but NOT in the overall balanced equation.
• It is FORMED in an early elementary step and consumed later.
• Intermediates are usually short life or have small lifetimes

Question 6

Molecularity

Answer 6

Number of reactants in an elementary step
1. Unimolecular-1 reactant
2. Bimolecular- 2 reactants
3. Termolecular- elementary step with 3 reactants

Question 7

How do you determine reaction order for elementary reactions

Answer 7

They are equal to the corresponding stoichiometric coefficients

Question 8

Is this a unimolecular or biomolecular: k[A]^2

Answer 8

BIMOLECULAR

Question 9

For a unimolecular reaction what is the rate equal to (in words and equation)

Answer 9

The total # of A molecules ([A]) x the probability for a A to react (k). Rate=k[A]

Question 10

What is the rate equal to for a bimolecular reaction (in words and numerical)

Answer 10

1. Rate is the total # of collisions between A and B molecules x the probability for a A+B to react (k)
2. Rate=k[A][B] or rate=[A]^2

Question 11

How do you find the toal number of collsions in a bimolecular reaction between A and B

Answer 11

[A] x [B]

Question 12

What is the rate for a termolecular reaction (number and words)

Answer 12

Total # of triple collisions (A colliding with a B-C complex)
Rate=k[A][B][C]

Question 13

For a termolecular reaction, How do you find:
1. The # of B-C complexes
2. The # of collisions for a given molecules A with any B-C complex

Answer 13

1. [B][C]
2. [B][C]

Question 14

1. Catalyst Definition
2. How do they work
3. Effect on Ea and k

Answer 14

1. A substance that increases the rate of a chemical reaction without itself being consumed
2. They work by reducing the reaction’s activation energy
3. With catalyst: Ea decreases, k increases

Question 15

What are enzymes and how do they work

Answer 15

Enzymes are efficient catalysts and catalyze biological reactions by forming a complex with substrate which has a lower reaction activation energy