Equilibrium

Question 1

What does the reversibility of chemical reactions depend on?

Answer 1

the activation energies of the forward & reverse reactions have to be both low enough that sufficient particles have energy for a successful collisions

Question 2

Open systems

2

Answer 2

• energy & matter transfer
• substances can be added or lost

Question 3

Closed systems

2

Answer 3

• energy transfer but not matter transfer
• substances can neither enter nor leave system

Question 4

Equillibrium

2

Answer 4

• rate of forward and reverse reactions are equal
• **concentration of species is constant **(a.k.a. dynamic equilibrium/steady state)

Question 5

What system can equilibrium occur in

Answer 5

closed system

Question 6

Equilibrium vapour pressure

Answer 6

pressure exerted by vapour will be constant
rate of evaporation = rate of condensation

Question 7

Equilibrium in solution

Answer 7

rate of crystallisation = rate of dissolving

Question 8

Physical equilibrium

Answer 8

• equilibrium vapour pressure
• equilibrium in solution

Question 9

Equilibrium constant formula

Answer 9

K= [products] / [reactants]

Question 10

What do you omit in the K constant

2

Answer 10

• solids & liquids
  unless whole equation is
• omit states

Question 11

What is mainly present at equilibrium if K«1

Answer 11

mainly reactants

Question 12

What is mainly present at equilibrium if K»1

Answer 12

mainly products

Question 13

What is mainly present at equilibrium if K=1

Answer 13

both reactants & products are at similar concentrations

Question 14

Is K dependent on rr

Answer 14

No

Question 15

What changes K

and effect of increasing this change

Answer 15

• temp
  increase temp = increase K value of endo & decrease K value of exo

Question 16

If Q = K

Answer 16

reaction is at equilibrium

Question 17

What is Q

Answer 17

reactant quotient
Q = [products] / [reactants]

Question 18

If Q < K

Answer 18

less products, more reactants
forward favoured

Question 19

If Q > K

Answer 19

more products, less reactants
reverse favoured

Question 20

Very briefly explain equilibrium using rr & collision theory

initially, in the middle, at equilibrium

Answer 20

• firstly forward rr is high bc high [reactants], whilst reverse rr=0 bc no products present
• decrease [reactants] = decrease forward rr & increase [products] = increase reverse rr (although not as much as forward)
• eventually equilibrium reached where forward rr = reverse rr

Question 21

What is the equilibrium constant

2- not equation

Answer 21

• provides info on relative concentration of reactants & products
• nothing to do with rr

Question 22

How are changes to concentration made

Answer 22

selectively adding or removing substance from the system
possibly thru additional reactions

Question 23

How are changes to total pressure/volume in gaseous systems made

Answer 23

raising/lowering volume or inserting more gas particles

Question 24

How is temperature changed

Answer 24

Adding or removing heat

Question 25

Le Chatelier's principle

Answer 25

when the **concentration** of any one species in an equilibrium is **altered** by a **change imposed** on the system, a **new equilibrium will form** in such a way that **partially counteracts** this imposed change

Question 26

Adding or removing catalyst ## Footnote shift in equilibrium

Answer 26

- catalysts reduce Ea by equal amounts - no shift in equilibrium | only affects rr, not []

Question 27

Add inert gas | not on constant pressure ## Footnote shift in equilibrium

Answer 27

- **increases total pressure**, yet **concentration** of reactants and products are **unchanged** - no change in forward or reverse RR so no shift in equillibrium

Question 28

Add or remove a solid/liquid part of the system ## Footnote shift in equilibrium

Answer 28

- no change in [] - no change in forward or reverse RR - no shift in equilibrium

Question 29

Adding something | e.g. add reactant gas ## Footnote shift in equilibrium - explain using RR

Answer 29

- increase [] - increase frequency of collisions between reactants - increase in initial forward RR (no effect on initial RR) - *equilibrium reestablishes at a higher rr*

Question 30

Removing something | e.g. removing a product gas ## Footnote explain using rr

Answer 30

- decrease [] = decrease frequency of collisions... - decrease rate of initial R rr & no effect on initial F rr

Question 31

Decrease volume ## Footnote shift in equilibrium - explain using rr

Answer 31

- increase [all gaseous species] (number of particles per unit volume) - increase initial F & R rr - whichever one has more moles of gaseous species is favoured (increase in concentration is more profound)

Question 32

Increase volume ## Footnote shift in equilibrium - explain using rr

Answer 32

- decrease [all gaseous species] (number of particles per unit volume) - decrease both intitial F & R rr - whichever one has a less significant decrease is favoured

Question 33

Decrease volume ## Footnote LCP

Answer 33

- increase concentration of gaseous species - side with **less gas is favoured** to counteract the imposed change

Question 34

Increase volume ## Footnote LCP

Answer 34

- decrease concentration of gaseous species - side with **more gas is favoured** to counteract imposed change

Question 35

Adding water ## Footnote shift in equilibrium - rr

Answer 35

- decreased [all aqueous species] - decrease in initial F & R rr - whichever decrease is less profound is favoured

Question 36

Increase temp ## Footnote shift in equilibrium - rr

Answer 36

- increase Ek.... increase rate in initial forward & reverse reactions - increase in endo is more profound than exo (bc **endo has a higher Ea**) - net endo favoured

Question 37

Decreasing temp ## Footnote shift in equilibrium - rr

Answer 37

- decrease Ek... decrease initial exo & endo rr - decrease in endo is more profound - **net exo favoured**

Question 38

One spike on graph

Answer 38

adding or removing something

Question 39

All spikes on graph

Answer 39

changing volume

Question 40

No spike on graph

Answer 40

Changing temp

Question 41

Effect on decreasing volume on pressure

Answer 41

increases pressure

Question 42

Final phrase miss adds to explanations

Answer 42

after some time, a new equilibrium is reached where the forward and reverse xn rates are equal and **higher/lower** than before the change

Question 43

Haber process equation

Answer 43

N2 + 3H2 ⇌ 2NH3 | all gases

Question 44

Is Haber process endo or exo

Answer 44

exo

Question 45

Haber process conditions | 3

Answer 45

moderate temp (350-550ºC) high pressure (15-35 MPa) catalyst (Fe/Fe2O3 and many more)

Question 46

Haber process economical concern

Answer 46

high temp & pressures significantly increase **energy** & **maintenance costs** to ensure reaction is carried out **safely** *adding catalyst allows reaction to proceed at decent rate at lower t & p conditions*

Question 47

Contact process

Answer 47

produce concentrated sulfuric acid

Question 48

contact process | 3 conditions + equation (for step 2)

Answer 48

2SO2 + O2 ⇌ 2SO3 exo all gas - mod temp (450ºC) - catalist (vandium oxide) - low pressure (1-2atm) - bc expensive and unsafe

Question 49

Model rr explanation | 4

Answer 49

- change in conc - how it affects collisions - how it affects rates of initial forward & reverse - new equilibrium being established

Question 50

What words not to include in rr

Answer 50

- shift - favours | USE IN LCP

Question 51

Is sublimation of iodine crystals open or closed system

Answer 51

open iodine vapour escaping

Question 52

Concerns with haber process | 2

Answer 52

- economics - safety

Question 53

Simple ways to favour forward in haber process

Answer 53

- high conc of N2 & H2 gas - removing NH3 product