physical chem; chemical equilibria, le chatliers principle & Kc

Question 1

what is a reversible reaction?

Answer 1

it’s a reaction that allows products to react to reform their original reactants

Question 2

explain how the forward reaction is shown on the conc/time graph

Answer 2

initially reactants are used up quickly but then slow down as their conc drops

Question 3

explain how the backwards reaction is shown on the conc/time graph

Answer 3

initially reactants are reformed slowly but the speed up as the conc of products increases

Question 4

define dynamic equilibrium

Answer 4

the rate of the forward reaction is the same as the rate of the backwards reaction in a closed system & the conc of products & reactants are the same

Question 5

what is a closed system?

Answer 5

none of reactants/products escape from reaction mixture

Question 6

what is an open system?

Answer 6

matter & energy can be lost to the surroundings

Question 7

how can equilibrium be reached in a solution?

Answer 7

can be reached in an open flask as amounts of material can be lost through evaporation

Question 8

how can equilibrium be reached for gases?

Answer 8

only in a closed system

Question 9

what is le chatlier’s principle?

Answer 9

if a reaction at equilibrium is subjected to a change in pressure, temperature or concentration, the position of equilibrium will shifts to counteract that change

Question 10

what are the effects of changes on conc on the position of equilibrium?

Answer 10

increased conc of reactant = shifts to the right to use it up & reduce its conc (more product produced)

increased conc of products = shifts to the left to use it up & reduce the conc (more reactants produced)

Question 11

define homogeneous equilibria

Answer 11

this is where reactants & products in the same state

Question 12

what are the effects of changes in pressure on the position of equilibrium?

Answer 12

increased pressure = shifts to side with fewest no.of gas particles

decreased pressure = equilibrium will shift to the side with the most no.of moles

Question 13

what are the effects of changes in temperature on the position of equilibrium?

Answer 13

increased temp = shifts in the endo direction to reduce the temp

decreased temp = shifts in the exo direction to increase the temp

Question 14

state the effects of catalysts on the position of equilibrium

Answer 14

no effect as catalysts will speed up the rate of the forward & backward reaction equally

Question 15

what effect do catalysts have on yield?

Answer 15

none, a catalyst will speed up the rate at which equilibrium is reached & has no effect on yield

Question 16

what are the conditions for making ethanol?

Answer 16

pressure = 60 atmospheres
temp = 300°
catalyst = phosphoric acid (H₃PO₄)

Question 17

explain the process of making ethanol by adjusting the temperature, referring to le chatelier’s principle

Answer 17

forward reaction is exothermic so decreasing the temp means equilibrium shifts to the right producing more ethanol

Question 18

state the limitation of adjusting the temperature to produce more ethanol

Answer 18

as the temp is lowered the rate is lowered as well

Question 19

explain the process of making ethanol by adjusting the pressure, referring to le chatelier’s principle

Answer 19

high pressure increases rate
high pressure & fewer no.of moles on the right means equilibrium would shift to the right producing more ethanol

Question 20

state the limitation of adjusting the pressure to produce more ethanol

Answer 20

high pressure environments are expensive

Question 21

how does temperature affect Kc?

Answer 21

Kc is only valid for 1 temp
changing the temperature will change equilibrium concs so Kc will change too

Question 22

how does temperature change affect the value of Kc in an equilibrium?

Answer 22

if temp change causes equilibrium to shift right Kc will increase

if temp change causes equilibrium to shift left Kc will decrease

Question 23

how does concentration affect Kc?

Answer 23

value of Kc is unaffected by any changes in conc

Question 24

how do catalysts affect Kc?

Answer 24

no effect on the value of Kc as catalysts speed up the forward & backwards reaction equally