topic 10+ 11: eqm 1 + 2

Question 1

what is dynamic equilibrium

Answer 1

• forwards and backwards reactinos occur at equal rates
• concentrations of reactants and products remain constant

Question 2

le chatelier’s principle

Answer 2

if a change happens the equilibrium will shift to try to reverse it

Question 3

increase in temp effect on eqm?

Answer 3

• shifts equilibrium in the ENDOTHERMIC direction

Question 4

difficulty with temp equilibrium

Answer 4

• low temperatures can give higher yield
• but slower rate
• so use a compromise temperature, OR LOW TEMP AND CATALYST

Question 5

Effect of pressure on equilibrium

Answer 5

• causes equilibrium to shift to the side with FEWER MOLES OF gas

Question 6

in industry, high temperatures and pressures are…

Answer 6

• EXPENSIVE (equipment and energy costs)

Question 7

effect of concentration on equilibrium

Answer 7

• increase in concentration of one thing means the POE will shift in the opposite direction on this

Question 8

effect of catalysts on equilibirum

Answer 8

NO EFFECT
- as speeds up rate of forwards and backwards reactions by same amount
- only speeds up rate at which equilibrium is achieved

Question 9

advantage of using a catalyst?

Answer 9

• speeds up rate
• SO CAN USE LOWER TEMP AND PRESSURES
• lower energy costs
• lower equipment costs

Question 10

strange way to increase yield?

Answer 10

• reversible reactions
• so recycle unreacted reactants

Question 11

Kc expression
eg
A + 2B = 3C

Answer 11

Kc = [C]^3 / [A][B]^2

Question 12

HOMOGENEOUS equilibirum

Answer 12

reactants and products all in same phase

Question 13

heterogeneous equilibrium

Answer 13

reactants and products not all in same phase

Question 14

in heterogeneous equilibrium, which do you include in Kc

Answer 14

GASES
- no solids or liquids

Question 15

when do you include water in Kc

Answer 15

• when water is a REACTANT, not a solvent
• otherwise its concentration remains constant so isnt included

Question 16

what can change Kc

Answer 16

ONLY THE TEMPERATURE!!!!!!!!

Question 17

What does it mean in terms of products and reactants if Kc is large

Answer 17

• more products than reactants
• eqm lies very far to the right

Question 18

which concentrations do you use in Kc

Answer 18

• the EQUILIBRIUM CONCENTRATIONS!!!!!!!

Question 19

when calculating equilibrium concentration, which volume do you use

Answer 19

TOTAL REACTION MIXTURE volume

Question 20

catalyst for preparing an ester with carboxylic acid and alcohol

Answer 20

dilute sulfuric acid

Question 21

method for Kc experiment making an ester

Answer 21

• use burettes to measure amounts and mix together carboxylic acid, alcohol, dilute sulfuric acid catalyst. LEAVE FOR A WEEK TO REACH EQUILIBIRUM
• Rinse volumteric flask with water
• transfer reaction mixture in through funnel, rinse w distilled water and transfer washings in. make up to the mark. stopper, invert and shake
• use pipete to put 25cm3 of this into conical flask, and add indicator
• burette with alkali
• titrate
• SODIUM HYDROXIDE WILL REACT WITH THE CATALYST AND ANY UNREACTED CARBOXYLIC ACID

Question 22

partial pressure of gas

Answer 22

mole fraction * total pressure

Question 23

Kp only applies for

Answer 23

GASES

Question 24

Value of K where reaction doesnt go

Answer 24

smaller than 10^10

Question 25

reaction goes to ocmpleteion K

Answer 25

k > 10^10

Question 26

delta S total

Answer 26

- entropy change of system + entropy change surrounding - = RlnK

Question 27

in industry is equilibirum ever reached?

Answer 27

NO - products are removes as they are formed - so not a CLOSED SYSTEM;

Question 28

give 3 reasons why product may be removed before equilibrium is reached

Answer 28

1. shifts POE to the right 2. decreases rate of backwards reaction 3. unreacted reactants can be recycled

Question 29

2 ways to improve yeild industrially (2)

Answer 29

- recycle unreacted products - remove product as its formed

Question 30

state and expain one benefit to the environment resulting from use of catalysts in industry (2)

Answer 30

- lower temp needed - less combustion of fuels, so fewer harmful emissions eg co2 ghgs

Question 31

if titre the same , what feature of equilibrium displayed?

Answer 31

- forwards and backwards reactions at same rate - conc products and reactants remain constant

Question 32

suggest why test tubes are sealed

Answer 32

- prevent evaporation

Question 33

why no need to have volume for this calc? (2)

Answer 33

- equal moles products and reactants - VOLUMES CANCEL

Question 34

why might a mixture lef tto sit go acidic?

Answer 34

absorbs CO2 from atmosphere

Question 35

how would you confirm a week is long enough to reach equilibiru ? (2)

Answer 35

- repeat exp and leave LONGER THAN A WEAK - titrate, titre should be the same

Question 36

haxard of hydrogen

Answer 36

flammable

Question 37

why not include solid in Kc

Answer 37

conc is constant

Question 38

why not include solid in Kp

Answer 38

solid doesnt exert pressure / presure is constant

Question 39

why might increasing pressure NOT affect rate(catalyst ) (2)

Answer 39

- reaction occurs on surface of catalyst - active sites saturated with reactants

Question 40

delta s total =

Answer 40

RlnK