Principles of Reversible Reactions

Question 1

define reversible rxns

Answer 1

chemical rxn where reactants react to form products, which in turn react to form reactants again under suitable conditions

Question 2

define dynamic equilibrium

Answer 2

occurs when rate of forward rxn = rate of backward rxn for reversible rnx
as a result, no change in amnt/conc of reactants & products

Question 3

chatelier’s principle

Answer 3

if a system at equilibrium is subjected to a change which disturbs it, system responds to counteract effect of change
- occurs ONLY when reaction is in closed system

Question 3

conditions (4)

Answer 3

1. conc/amnt substance
2. temp
3. pressure (GASES ONLY)
4. addition of catalyst

Question 4

answering guidelines

Answer 4

1. forward/backward rxn favoured, reason, include temp if exo/endothermic
2. equilibrium shift left/right
3. to counteract effect of change

Question 4

conc.

Answer 4

always shift to side w/ lesser after change
- add right, shift left, forward rxn favoured, to decrease amnt right

Question 4

temp (of surroundings)

Answer 4

triangle h = forward rxn
- temp surroundings DOWN, exothermic to raise temp again, shift to increase temp, release energy into system

Question 5

pressure

Answer 5

ONLY FOR GASES!!! calc no. moles on each side
- increase pressure, shift to less moles to decrease pressure

Question 6

catalyst

Answer 6

DOES NOT CHANGE RATE EQUILIBRIUM, only speeds up rxns
- lowers Ea of forward/backward rxns by same extent, allow equilibrium reach faster

Question 7

Haber process (nh3 manufacture)

Answer 7

• n2 (g) + 3h2 (g) <-> 2nh3 (g) [EXOTHERMIC]
  reactants & sources:
• n2: frac distillation of liquid air
• h2: catalytic cracking of long-chain hydrocarbons from petroleum

Question 8

reasons for conditions of Haber process

Answer 8

high pressure
- shift equilibrium right, which has less moles of gas, UP yield
- expensive tho
moderate temp (cannot too high bc exothermic)
- UP rate of rxn
- higher temp causes particles to have more kinetic energy & move faster
- frequency of effective collisions UP between particles
catalyst
- UP rate of rxn
- powdered catalyst UP surface area volume ratio

Question 8

biological application

Answer 8

anaerobic respiration: o2 transport to cells, combine w/ glucose, metabolized to co2, moves back to lungs
- haemoglobin takes up o2, becomes loosely bound in complex oxyhaemoglobin
- o2 conc reduced by 50% at ends of capillaries delivering blood to tissues
- equilibrium shift LEFT, RELEASE O2 to diffuse into cells