Topic 10

Question 1

What is the purpose of potential energy surface plots?

Answer 1

visualize the energy changes as a reaction proceeds
Make predictions about likely pathways and reaction success

Question 2

What are some variables you can find on a potential energy surface plot?

Answer 2

equilibrium bond lengths, bond lengths at transition states, and minimum activation enegry

Question 3

What does the dashed line represent on a potential energy surface plot?

Answer 3

The lowest energy pathway from start to finish (minimum energy pathway

Question 4

If the end point is lower in energy than the starting point, is the reaction endo/exothermic?

Answer 4

exothermic

Question 5

What is the saddle point on a potential energy surface plot?

Answer 5

The transition state/activation energy
unhappy here because it had to increase in energy

Question 6

What letter is enthalpy?

Answer 6

H

Question 7

What letter is entropy?

Answer 7

S

Question 8

What does the units on gibbs free energy have to be?

Answer 8

au (hartrees)

Question 9

How many kJ/mol is in a hartree?

Answer 9

2625.5kJ/mol=1au

Question 10

What is the Eyring-Polanyi equation formula?

Answer 10

k_rxn=(kappak_BT/h)*e^(-deltaG dagger/RT)

Question 11

What does the Eyring-Polanyi equation tell us?

Answer 11

predicts the rate constant

Question 12

What is the equation for Gibbs free energy?

Answer 12

deltaG=deltaH-TdeltaS

Question 13

Where do you find detaG dagger on a reaction coordinate diagram?

Answer 13

from reactant line to the top of the hill

Question 14

Where do you find deltaGrxn on a reaction coordinate diagram?

Answer 14

from product line to reactant line

Question 15

Where is the transition state on a reaction coordinate diagram?

Answer 15

The top of the peak

Question 16

What does it mean when a reaction coordinate diagram has a large ‘hill’?

Answer 16

a big hill makes a slow reaction rate and a small rate constant

Question 17

If reactants are higher than products, is the reaction ender/exergonic?

Answer 17

exergonic

Question 18

What is the Y axis on a reaction coordinate diagram?

Answer 18

G

Question 19

What is is X axis on a reaction coordinate diagram?

Answer 19

rxn coordinates

Question 20

What does delta G dagger mean?

Answer 20

activation energy

Question 21

Explain spontaneity.

Answer 21

It does not mean that a reaction is going to happen, it just means that the products are lower thermodynamically/more stable than the reactants
It does not guarantee that the reaction is fast

Question 22

If gibbs free energy decreases, is the reaction ender/exergonic and is it spontaneous or not?

Answer 22

exergonic and spontaneous

Question 23

How is the transition state on a reaction coordinate diagram also a ‘saddle point’?

Answer 23

It is unhappy but could have been more unhappy
It is the least unhappy point of the options
The most stable intermediate of a rxn
It is the highest in one respect but the lowest in another