Chapter 5 - Chemical Kinetics

Question 1

what determines whether a reaction will occur without outside assistance?

Answer 1

the change in Gibb’s free energy

Question 2

if a reaction is spontaneous, does that mean it will run quickly?

Answer 2

no

Question 3

what is the mechanism of a reaction?

Answer 3

the steps a reaction takes to get from reactants to products

Question 4

what is the sum of the mechanism of a reaction?

Answer 4

the overall reaction (equation)

Question 5

what are intermediates of a reaction?

Answer 5

molecules formed in the middle of a mechanism but not present in the overall reaction, real molecule formed but may not be present for a long time

Question 6

what is the rate determining step?

Answer 6

slowest step in a proposed mechanism, acts like a kinetic bottleneck, prevents overall reaction from proceeding any faster than the slowest step

Question 7

what is the collision theory of chemical kinetics?

Answer 7

rate of reaction is proportional to the number of collisions per second between the reacting molecules

Question 8

what makes a collision effective for a reaction to occur?

Answer 8

molecules must collide together in the correct orientation and with sufficient energy to break their existing bonds and form new ones

Question 9

what is the activation energy?

Answer 9

minimum energy of a collision necessary for a reaction to take place

Question 10

what is the equation for the rate of a reaction?

Answer 10

k= Ae^Ea/RT 
A= frequency factor
Ea= activation energy
R=ideal gas constant
T= temp in kelvin

Question 11

what happens as frequency factor increases?

Answer 11

rate increases

Question 12

does reaction rate increases or decrease with an increase in temperature?

Answer 12

increase

Question 13

how can the frequency factor be increased?

Answer 13

by increasing the number of molecules in a vessel

Question 14

what is the transition state?

Answer 14

when molecules collide with energy greater than or equal to the activation state, they enter a state in which old bonds are weakened and the new bonds begin to form; will then dissociate into products, fully forming the new bonds, has greater energy than the products and reactants,
o Transition states are theoretical constructs that exist at the point of maximum energy, rather than distinct identities with finite lifetimes
o Can dissociate into products or revert back to reactants without any additional energy input
o Exist at peak of the energy diagram

Question 15

what is the free energy change of a reaction?

Answer 15

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

Question 16

what is an exergonic reaction?

Answer 16

negative change in Gibbs free energy

Question 17

what is an endergonic reaction?

Answer 17

positive change in Gibbs free energy

Question 18

what defines the activation energy?

Answer 18

Difference in free energy between the transition state and the reactants is the activation energy of the forward reaction, difference in free energy between the transition state and the products is the activation energy of the reverse reaction

Question 19

what happens as the concentration of reactants increases?

Answer 19

reaction rate increases

Question 20

what happens as temperature is increased

Answer 20

increases the reaction rate for nearly all reactions

Question 21

why does increasing the temperature increase the reaction rate?

Answer 21

increases the average kinetic energy of the molecules

Question 22

what will happen if the temperature is too high for a reaction?

Answer 22

catalyst may denature and then reaction rate will plummet

Question 23

are all reactions temperature dependent?

Answer 23

yes, all reactions have a temperature for optimal activity

Question 24

what properties of a medium can affect the reaction rate?

Answer 24

aqueous/nonaqueous, physical state (solid, liquid, gas), polar/nonpolar

Question 25

what is a catalyst?

Answer 25

substances that increase the rate of a reaction without themselves being consumed in the reaction; Interact with the reactants and stabilize them to reduce the activation energy

Question 26

what is a homogenous catalyst?

Answer 26

in same state (liquid, gas, solid) as the reactants

Question 27

what is a heterogenous catalyst?

Answer 27

in a different state (liquid, gas, solid) as the reactants

Question 28

do catalysts affect both the forward and reverse reactions?

Answer 28

yes, lowers activation energy for both

Question 29

do catalysts affect equilibrium?

Answer 29

no

Question 30

can catalysts affect spontaneity of a reaction?

Answer 30

no; No impact on the free energies of the reactants or the products of the difference between them ,Only make spontaneous reactions move more quickly towards equilibrium