Chem2 - Kinetics and Equilibria

Question 0

What is the activation energy on an enthalpy profile diagram?

Answer 0

It is the height of the peak between reactants and products

Question 1

What is needed for a reaction to take place?

Answer 1

• collide in the right direction

- collide with equal to or above the activation energy

Question 2

What is a Maxwell-Boltzmann distribution curve?

Answer 2

Its a curve which shows the different energies of the molecules within a sample of a gas, only so many have equal to or above the Ea

Question 3

How does an increase in temperature affect a Maxwell-Boltzmann curve?

Answer 3

• shifts to the right
• peak a bit lower/flatter as same n# of molecules
• therefore more molecules have equal to or above Ea

Question 4

How does an increase in pressure affect Maxwell-Boltzmann distribution curve?

Answer 4

• same curve but higher all over

- as more particles in sample

Question 5

How does an increase in concentration affect Maxwell-Boltzmann distribution curve?

Answer 5

• same as increased pressure
• same as curve but higher all over
• more molecules in sample

Question 6

Where is the average kinetic energy of a molecule on a Maxwell-Boltzmann curve?

Answer 6

Slightly to the right of the peak

Question 7

What does a catalyst do?

Answer 7

It speeds up the rate of a reaction without itself being consumed or chemically changed

Question 8

How does a catalyst have it’s effect?

Answer 8

It offers an alternative reaction pathway with a lower activation energy

Question 9

How does a catalyst affect an enthalpy profile diagram?

Answer 9

It makes the height of the peak between reactants and products smaller

Question 10

How does a catalyst affect a Maxwell-Boltzmann curve?

Answer 10

Moves activation energy to the left, so more molecules have equal to or higher than Ea

Question 11

p51

Answer 11

p51

Question 12

What is the most probable energy of a molecule on a Maxwell-Boltzmann distribution curve?

Answer 12

Enthalpy at the peak

Question 13

What is the rate equation of a reaction with reactants A and B, order of reaction 1 wrt A and 2 wrt B (1)

Answer 13

Rate of reaction = [A][B]^2

Question 14

Define the term rate of reaction (1)

Answer 14

Change in concentration of reactants per unit time

Question 15

How do you find out the order of each in the rate equation (when its not given)? (2)

Answer 15

Have no rate equation therefore can only work out using table of results!
~see how changing its concentration changes the rate of reaction
~if you x2 its conc and the rate doubles it has an order of 1, if x2 conc and rate quadruples it has order 2 (2^2 = 4), if x3 conc and rate multiplies by 9 then it has order 3 (3^2 = 9) etc

Question 16

How do you work out the total order of reaction? (1)

Answer 16

~add up all the orders of reaction for the reactants in the rate of reaction equation

Question 17

How do these factors affect k?

• > increase temperature
• > increase pressure (all gases)
• > increasing concentration of one of the reactants
• > adding a catalyst (4)

Answer 17

~temp increase, k increases
~pressure increase, k unchanged
~concentration increases, k unchanged
~k increases unless catalyst in rate equation in which case k is unchanged