Effect of changes Flashcards
(16 cards)
H2(g) + I2(g) ->-< 2HI(g)?
- 1:1 ratio
- 573K
- closed container
- H2 & I2 start to react when heated to form HI
- w increasing time - concs. H2 & I2 decrease so - rate of forward reaction decreases
- w increasing time - conc. HI increases so - rate of backward increases
- eventually rates of forward & backward reactions become equal & no further change in concs.
- now in dynamic equilibrium
Dynamic equilibrium conditions?
- reaction must be reversible
- reaction mix must be in closed container
Features that define Dynamic equilibrium?
- both forward & backward reactions r continuously occurring
- rate of forward reaction equal to rate of backward
- concs. reactants & products remain constant
(f & b reactions same time & same rate)
Effect of change in concentration?
- increase conc. reactant - eq pos shifts to right
- decrease conc. reactant - eq pos shifts to left
- increase conc. product - eq pos shifts to left
- decrease conc. product - eq pos shifts to right
(increase conc. reactants - rate of forward reaction increases - more product will form - conc. product increases - rate of backward r increase - new eq established - pos has moved to right)
Effect of increase in pressure?
- more moles of reactants - eq pos shifts to right
- fewer moles of reactants - eq pos shifts to lefts
- same moles - no change
Effect if change in temperature?
forward reaction is exothermic:
- increase temp - pos of eq shifts to left
- decrease temp - eq pos shifts to right
- favours endothermic reaction
- increase in rate of endo greater than exo as - reactions w high Ea (aka endo) more sensitive to temp changes than those w low Ea
Effect of addition of catalyst?
- rate of both forward & backward reactions increase
- increase in rate same for both
- pos of eq not altered
- adv of adding at start: reduces time required to establish eq
Industrial processes: for maximum profits, reactants into products must happen?
- as quickly as poss
- as completely as poss
Haber process?
- N2(g) + 3H2(g) -><- 2NH3
- 450 degrees Celsius
- 200 atm
- catalyst inefficient at low temps
- but very high temp uneconomical- may also reselt in decreased yield as - increase in rate of backward reaction>forward
- so compromise of 450
- higher the press, larger energy costs
- the lower the press, lower yield
- so compromise of 200
Homogeneous v heterogeneous systems?
homo - all components r in the same phase
hetero - atl 2 diff phases r present
The equilibrium constant, Kc (Homogeneous)?
e.g. H2(g) + I2(g) -><- 2HI(g)
Kc = [HI(g)]^2 /
[H2(g)] [I2(g)]
- concs. of RHS of eq on numerator (products)
- concs. LHS on denominator (reactants)
- molar values in front of each species r powers
Homogeneous systems - Kc?
- if eq flipped so 2HI on RHS K’c = reciprocal of Kc
- if no. moles on eq changes e.g. halved (so - no ^2) - K’‘c = square root of Kc
Heterogeneous systems - Kc?
solid & pure liquids not included in kc expression
Effect of catalyst on Kc?
- no effect on value
- speeds up forward & reverse reaction
- speeds up rate at which equilibrium established
The contact process?
- manufacture of sulfuric acid
SO2 (g) + 1/2 O2 (g) –> SO3(g) - involves reaction between sulfur dioxide & O2 at surface of solid vanadium(V) oxide (V2O5) catalyst
- forward reaction exo so - low temp favour high yield
- but catalyst ineffective at low temps so moderately high 450 used
- higher press increase yield as fewer moles on RHS so - 2atm
(unnecessary for press higher than ts as yield alr very high)
Mechanism:
SO2 + V2O5(s) -><- SO3 + V2O4 (s)
V2O4(s) + 1/2 O2 -><- V2O5(s)
Only thing that changes equilibrium constant?
temperature
