Chapter five

Question 1

Gibbs free energy

Answer 1

This change in G indicates whether a reaction can occur by itself. In other words, is it spontaneous.

Question 2

Intermediate

Answer 2

This is a compound (or a step) that does not appear in the overall reaction. It is only visible when determining the steps, or the mechanism of the reaction.

Question 3

Rate-determining step

Answer 3

The slowest step in the reaction. It determines the rate of the whole reaction.

Question 4

Rate of reaction

Answer 4

Proportional to the number of collisions per second between reacting molecules.

= (Z)(f)

where Z = total number of collisions per second
where f = the fraction of collisions that are effective

Question 5

Effective collision

Answer 5

A collision that forms new products. This only occurs if the molecules collide in the correct orientation and with enough energy to break old bonds/form new ones.

Question 6

Activation energy (Ea) or energy barrier

Answer 6

The minimum energy necessary for a reaction to proceed.

Question 7

Transition state

Answer 7

When molecules collide with energy equal to (or greater than) the activation energy, they form a transition state in which old bonds are broken and new bonds are formed.

This has the highest energy.

Can either dissociate into products OR revert back.

Question 8

Free energy change

Answer 8

The difference between the free energy of reactants and the free energy of products.

Positive = endergonic = energy is absorbed
Negative = exergonic = energy is lost

Question 9

Impact of concentration on rate of reaction

Answer 9

Greater concentration of reactions = more collisions

This leads to an increase in the frequency factor (A) and thus, an increased rate!

Question 10

Impact of temperature on rate of reaction

Answer 10

Reaction rate will increase with a higher temperature because it increases the kinetic energy.

Occasionally, the reaction rate with DOUBLE for every increase by 10 degrees. But, this is not for all reactions. There is an optimal temperature depending on the reaction.

Question 11

Impact of medium on rate of reaction

Answer 11

Some molecules are more likely to collide in (aq) or not (aq) environments.

Generally, polar solvents are preferred because their molecule dipole polarizes the bond of reactants, lengthening and weakening the bonds, thus increasing rate.

Question 12

Catalysts

Answer 12

Function to increase rate without being consumed in the reaction. They interact with the reactants, either to absorb them or introduce intermediates. Catalysts reduce activation energy.

Question 13

Homogenous v. heterogenous catalysts

Answer 13

Homogenous catalysts = same phase as the compound they are acting on (s, l, g)

Heterogenous catalysts = independent phase

Question 14

Rate law

Answer 14

= k[A]^x[B]^y

k = rate constant
x and y = orders of the reaction, not the same as the coefficients

Question 15

Two cases in which coefficients equal the order

Answer 15

1. Single step, reflective of the entire process
2. When the complete reaction mechanism is given and the rate-determining step is indicated

Question 16

Zero-order reaction

Answer 16

Rate of reaction is independent of changes in A and B

Rate = k[A]^0[B]^0
where k = M/s

Temperature and the addition of a catalyst are the only things that can change the rate.

On a time v. concentration graph, the slope is linear.

Question 17

First-order reaction

Answer 17

Rate of reaction is proportional to one reactant, such that doubling the concentration of one reactant results in doubling of rate.

Rate = k[B]^1 or Rate = k[A]^1
where k = s-1

Reaction begins when the molecule undergoes a change by itself (e.g., radioactive decay)

On a time v. concentration graph, the slope is non-linear. On a time vs. ln(concentration) graph, the slope is linear.

Question 18

Second-order reaction

Answer 18

Rate of reaction is proportional to the concentration of two reactants OR the square concentration of one reactant.

Rate = k[A]^1[B]^1 or Rate = k[A]^2 or Rate = k[B]^2
where k = m-1s-1

Often suggests a physical collision

On a time v. concentration graph, the slope is non-linear. On a time vs. [1/concentration] graph, the slope is linear.

Question 19

Mixed-order reactions

Answer 19

Refers to rate orders that vary over the course of the reaction.