chapter 10

Question 1

rate of reaction=

Answer 1

change in conc/ time

mol dm-3/s= mol dm-3 s-1

Question 2

how does increasing the concentration affect ROR

Answer 2

• increase in conc increases the number of particles in the same volume, closer together- collide more frequently
• more effective collisions= faster ROR

Question 3

how does increasing the pressure of a gas affect ROR

Answer 3

the concentration of the gas molecules increases, closer together and collide more frequently, leading to more effective collisions

Question 4

catalyst

Answer 4

a substances that changes the ROR without undergoing any permanent change itself
-not used up
-may react with a reactant to form an intermediate or may provide a surface on which the reaction can take place
-at the end the catalyst is regenerated
provides an alternative reaction pathway of lower activation energy

Question 5

homogeneous catalysts

& 2 examples

Answer 5

has the same physical state as the reactants

• reacts with the reactants to from an intermediate. the intermediate then breaks down to give the product and regenerates the catalyst
• making esters with a sulfuric acid catalyst
• ozone depletion- cl radicals as catalyst

Question 6

heterogeneous catalysts

Answer 6

has a different physical state from the reactants, usually solid. reactant molecules are adsorbed onto the surface of the catalyst, after reaction the product molecules leave the surface of the catalyst by desorption

Question 7

examples of heterogeneous catalysts

3

Answer 7

• Fe in harbour process
• Ni in hydrogenation of alkenes
• vanadium oxide in the contact process

Question 8

features of the Boltzmann distribution

Answer 8

• curve starts at the origin- no molecules have zero energy
• the area under the curve is equal to the total number of molecules
• there is no maximum energy for a molecule- curve doesn’t meet the axis

Question 9

Boltzmann distribution and temperature

Answer 9

at higher temp:

• more molecules have an energy greater than or equal to the activation energy
• greater proportion of collisions will lead to a reaction increasing the ROR
• collisions more frequent- moving faster

Question 10

Boltzmann distribution and catalysts

Answer 10

a catalyst provides an alternative reaction route with a lower activation energy
- greater proportion of molecules have energy equal to or greater than the activation energy

Question 11

in dynamic equilibrium

Answer 11

• the rate of the forward reaction is equal to the rate of the reverse reaction
• the concentrations of reactants and products do not change

Question 12

le chatelier’s principal

Answer 12

states that when a system in equilibrium is subjected to an external change the system readjusts itself to minimise the effect of that change.

Question 13

effect of concentration on equilibrium

Answer 13

A + B C + D
increase conc of A or B, decrease conc of C or
-left

Question 14

effect of temp on equilibrium

Answer 14

• an increase in temperature shifts the equilibrium position in the endothermic direction
• decrease in temperature shifts the equilibrium position in the exothermic direction

Question 15

effect of pressure on equilibrium

Answer 15

increasing the pressure of the system will shift the position of equilibrium to the side with fewer molecules, reducing the pressure

Question 16

effect of catalyst on equilibrium

Answer 16

does not change position

speeds up rates of forward and reverse reactions equally so equilibrium will be reached faster

Question 17

Kc=

Answer 17

[C]c [D]d / [A]a [B]b

Question 18

what does Kc value mean

Answer 18

• 1 means the position of equilibrium is halfway between the reactants and products
• Kc > 1 indicates position is towards the products
• Kc < 1 position is towards the reactants