1.6 equilibria and redox reactions

Question 1

what is dynamic equilibrium?
when does it occur?

Answer 1

when the forward and backward rate are equal and the conc of reactants and products isn’t changing.
closed system at constant temp

Question 2

what is Le Chatelier’s principle?

Answer 2

if a reaction at equilibrium is subjected to a change in conc, pressure or temp, position of equilibrium shifts to counteract the change.

Question 3

what happens if you increase the conc of a reactant in a reaction at equilibrium?

Answer 3

equilibrium tries to get rid of the extra reactant by making more product so equilibrium shifts right. vice versa for increasing conc of product or for decreasing them.

Question 4

what happens if you increase the pressure of a reaction at equilibrium?

Answer 4

only affects equilibria including gases
equilibrium shifts to side with fewer gas molecules to reduce the pressure. vice versa for decreasing pressure

Question 5

what happens if you increase the temperature of a reaction at equilibrium?

Answer 5

equilibrium shifts in endothermic direction (positive delta H) to absorb this heat. vice versa for decreasing temp (moves in exo direction to replace heat.

Question 6

example of reversible reactions

Answer 6

page 127 and 128 of text book

Question 7

what are the conditions of making ethanol from ethene and steam? why are they like this?

Answer 7

high pressure so forward reaction is favored (less molecules on left) but expensive so 60 atm is a compromise of max yield and min cost
low temp as forward is exo and lower temp shifts it in exo direction but that means slow ror so 300 as compromise of yield and ror
phosphoric acid catalyst
small bit of ethene reacts each time so reused

Question 8

conditions of making methanol from carbon monoxide and hydrogen
why?

Answer 8

50-100 atm
250 degrees c
catalyst of mixture of copper, zinc oxide, aluminium oxide
compromise between high yield and low cost

Question 9

What is Kc? what is the equation of the reaction and Kc?

Answer 9

the equilibrium constant (at that specific temp)
it is a ratio worked out from all concs of reactants and products once equilibrium is reached
aA + bB = dD + eE (reversible arrow)
Kc = [D]^d x [E]^e / [A]^a x [B]^b

Question 10

what does [A] mean?
what does a mean?

Answer 10

the conc of A in moldm-3
the number of moles of a

Question 11

how to find equilibrium conc?

Answer 11

ICE method
initial moles, change in moles, end moles (at equilibrium) (use ratio to work out change in moles)
divide all end moles by volume to find conc

Question 12

why might is not matter if you arent given volume in Kc question?

Answer 12

if there are no units then the volumes would all cancel in the equation for Kc

Question 13

how to find units for Kc?

Answer 13

put units into Kc instead of numbers and simplify

Question 14

how can you find equilibrium conc from Kc?

Answer 14

put all values in and rearrange to solve

Question 15

what factors affect equilibrium position?

Answer 15

concentration, pressure, temperature

Question 16

why does a catalyst not affect the equilibrium position?

Answer 16

it increases the rate of the forward and backward reactions by the same amount

Question 17

does temperature affect value of Kc?

Answer 17

yes.
if the change results in more product formed, Kc will rise
if it means less product is formed, Kc will fall
this is why Kc is at a given temperature

Question 18

does concentration affect value of Kc?

Answer 18

no

Question 19

does pressure affect value of Kc?

Answer 19

no

Question 20

does adding a catalyst affect value of Kc?

Answer 20

no

Question 21

what is a redox reaction?

Answer 21

reduction and oxidation happen simultaniously

Question 22

what is an oxidising agent?
what is a reducing agent?

Answer 22

oxidising- accepts electrons and gets reduced
reducing- donates electrons and gets oxidised

Question 23

what is the oxidation state of an element?

Answer 23

total number of electrons an element has donated or accepted

Question 24

what is the oxidation state of uncombined elements and elements bonded to just an identical atom?

Answer 24

0

Question 25

what is the oxidation state of a monoatomic ion?

Answer 25

the same as its charge

Question 26

what is the oxidation state of compounds or compound ions?

Answer 26

the sum of oxidation states of all the atoms- also equal to the charge of the compound

Question 27

what are the oxidation states usually of the following/ what are the exceptions?
group 1 metals
group 2 metals
flourine
(hydrogen, oxygen, chlorine and exeptions)

Answer 27

group 1 metals- +1
group 2 metals- +2
flourine- -1
hydrogen +1 unless in metal hydrides
oxygen -2 unless in peroxides/ compounds with F
chlorine -1 unless in compounds with O or F

Question 28

how do you find oxidation state from systematic names?

Answer 28

shown as roman numerals in brackets following element they correspond with eg iron(II) sulphate and iron (III) sulphate

Question 29

what is a half equation?

Answer 29

equation showing electrons to balance charges

Question 30

what is a redox equation?

Answer 30

equation showing oxidation and reduction

Question 31

how do you work out redox equations?

Answer 31

combine the oxidation and reduction half equations making sure they both have same number of electrons (can multiply whole equation by a common factor) then cancel out electrons

Question 32

how to write half equations

Answer 32

check if element being oxidised is balanced
add water molecules to balance oxygen atoms in the equation
add hydrogen ions to balance the hydrogen atoms in the equation
add electrons to conserve the charge
use oxidation states/ gain or loss of electrons to see if oxidation/ reduction occured