5.1 Qualitative understanding of equilibrium

Question 1

a reaction “goes to completion” when:

Answer 1

one reactant is used up completely

Question 2

static equilibrium

Answer 2

(1) reaction goes to completion
(2) zero velocity (no net movement of P and R)

Question 3

dynamic equilibrium

Answer 3

(1) reaction does not go to completion
(2) constant velocity (P and R still participating in reaction)

Question 4

conditions for dynamic equilibrium

Answer 4

1. A reversible reaction
2. A closed system
3. Macroscopic properties stay the same
4. Concentrations of substances are constant

Question 5

formation reaction slowing to equilibrium

Answer 5

concentration of reactants decrease > successful collisions decrease > rate of products produced decreases eventually to equilibrium

Question 6

dissolution reaction slowing to equilibrium

Answer 6

• products reverse into reactants BUT:
  (less reactants available) > reverse reaction slows to equilibrium

Question 7

non-equilibrium systems

Answer 7

1. Products are no longer in the system e.g. an open system.
2. Products do not react with each other due to their highly stable nature.
3. Forward reaction has a negative enthalpy change and positive entropy change.

Question 8

2 examples of non-equilibrium systems

Answer 8

combustion and photosynthesis

Question 9

4 stresses/factors

Answer 9

(1) concentration
(2) partial pressure (gas),
(3) total gas pressure (change in volume) or
(4) temperature

Question 10

in terms of collision theory, the number of successful collision between the reactants to produce products, and between products to produce reactants are…

Answer 10

equal at equilibrium

Question 11

effect of a catalyst on equilibrium

Answer 11

decreases time to reach equilibrium

Question 12

increasing concentration of a reactant shifts the equilibrium…

Answer 12

right to make more products

Question 13

Le Chatelier’s principle

Answer 13

a system responds to counteract a disruption to the system by establishing a new equilibrium

Question 14

collision theory for increasing concentration of reactants

Answer 14

increased concentration = increased frequency of collisions = increased forward rate, then equilibrium

Question 15

effect of dilution on equilibrium

Answer 15

decreased concentration = system favours the side with more moles

Question 16

increasing pressure is the same as:

Answer 16

increasing concentration

Question 17

relationship between pressure and volume

Answer 17

inversely proportional (Boyle’s law)

Question 18

increased P = decreased V = shift to…

Answer 18

side with LESS gas moles

Question 19

decreased P = increased V = shift to…

Answer 19

side with MORE gas moles

Question 20

increasing T = shift to…

Answer 20

endothermic side (to absorb the T)

Question 21

decreasing T = shift to…

Answer 21

exothermic side (to produce more T)

Question 22

the only 2 stresses that affect can rate of reaction

Answer 22

temperature and catalysts

Question 23

scientific way to say “all molecules/atoms/ions in an equation”

Answer 23

all chemical species involved

Question 24

scientific way to say “where the equilibrium shifts to”

Answer 24

“the position of equilibrium”

Question 25

if 1 mol of reactant shifts 2 moles up on a graph, then 1 mol of product will…

Answer 25

shift 2 moles down

Question 26

cobalt chloride equilibrium equation and colours

Answer 26

hydrated cobalt solution + chloride ⇌ cobalt chloride + water
Co(H2O)6 +2(aq) + 4Cl-(aq) ⇌ CoCl4 -2(aq) + 6H2O(l)

hydrated cobalt is pink
cobalt chloride is blue

Question 27

formation of cobalt chloride is exo or endo?

Answer 27

endothermic

Question 28

nitrogen dioxide equilibrium equation and colours

Answer 28

dinitrogen tetroxide ⇌ nitrogen dioxide
N2O4(g) ⇌ 2 NO2(g)

LHS colourless
RHS brown

Question 29

formation of nitrogen dioxide is exo or endo?

Answer 29

endothermic