CHEMICAL EQUILIBRIUM
reversible reaction: forward & reverse reaction under same condition (forward reaction: reactants > products, reverse reaction: products > reactants)
dynamic equilibrium: state reached by reversible reaction when forward reaction rate equals reverse reaction rate
for reversible reaction-
reactants form products > rate of forward reaction decreases (conc of reactant decrease) (same w/ products)
forward reaction: aA + bB >k₁> cC +dD     rate = k₁[A]^a[B]^b
reverse reaction: cC +dD >k _-1> aA + bB     rate = k _-1[C]^c[D]^d
[both forward & reverse reaction assumed single-stepped reactions]
finally stable state where forward reaction rate = reverse reaction rate > no change in conc > dynamic equilibrium
at dynamic equilbm:     k₁[A]^a_eq [B]^b_eq = k _-1[C]^c_eq [D]^d_eq     [ ]_eq = molar conc at eqbm
Equilibrium constant
-in terms of equilbm molar conc, K_C
aA + bB >k₁> cC +dD
aA + bB <k _-1< cC +dD     [states: (l), (g), (aq)]
at dynamic eqbm: rate of forward reaction = rate of reverse reaction
k₁[A]^a_eq[B]^b_eq = k _-1[C]^c_eq[D]^d_eq
k₁/k _-1 = K_C = [C]^c_eq[D]^d_eq/[A]^a_eq[B]^b_eq
K_C: const w/ const temp
solid reactant not included as [solid] is constant as density of solid is const
K_C: does not indicate rate of reaction
-in terms of equilbm partial pressure, K_P
only (g) reactants / products considered
pV = nRT => p = nRT/V => p n/V at const temp
pressure [molar conc] => p_eq [molar conc]_eq (equilbm partial pressure of gas equilbm molar conc of gas)
aA(g) + bB(g) + … <> rR(g) + sS(g) +…
at dynamic eqbm:       K_P = [p_R]^r_eq[p_S]^s_eq / [p_A]^a_eq[p_B]^b_eq

Factors affecting position of equilbm
-molar conc, -pressure, -temp
Le Chatelier's Principle: when a reversible reaction is in dynamic equilibm and if a factor affecting equilbm is changed, the equilbm position will shift in such a way to oppose/cancel the change
(1)concentration
conc of product increase > equilbm shifts to reduce product conc > reverse reaction favoured > more reactants
-rate equilbm reached affected (rate conc)
-K_c / K_p unaffected
-equilbm composition changed
(2)pressure
temp, vol: const
pV = nRT => p n
pressure increase > increase # of moles
pressure increased > equilbm shifts to reduce pressure > reaction w/ less moles of formed favoured (less moles => less pressure)
-rate equilbm reached affected (rate pressure)
-K_c / K_p unaffected
-equilbm composition changed (unless total # of moles on each side are equal, eg 2HI <> H₂ + I₂)
(3)temperature
temp increase > equilbm shifts to favour endothermic reaction (heat used up)
-rate equilbm reached affected (rate temp)
-K_c / K_p affected
-equilbm composition changed (unless reaction has no heat change)
Positive catalyst: increases rate of forward and reverse reactions by same rate
-rate equilbm reached affected (rate temp)
-K_c / K_p unaffected
-equilbm composition unchanged

Haber process
N₂(g) + 3H₂(g) <> 2NH₃(g) H = -92 kJ/mol
pressure: high > more ammonia produced & equilbm obtained faster
high pressure > more expensive maintenence (thicker walls, stronger pipes)
temperature: lower temp > more ammonia produced but slower rate of attaining equilbm
temp high enough to obtain equilbm at a reasonable rate
compromised conditions;
temp: 450°C
pressure: 250 atm
conc: 1 mol N₂ to 3 mol H₂
catalyst: finely divided reduced Fe
15% of reactants converted

Contact process
2SO₂(g) + O₂ <> 2SO₃(g) H = -197 kJ/mol
pressure: high > more SO₃ produced & equilbm obtained faster
higher pressure: -increase cost of maintenance, -SO₂ & SO₃ liquefy (due to non-ideal F of attraction)
temperature: lower temp > more sulphure trioxide produced but slower rate of attaining equilbm
temp high enough to obtain equilbm at a reasonable rate
compromised conditions;
temp: 450°C
pressure: 2 atm (higher pressure doesn't increase yeild much)
conc: excess O₂ to convert as much sulphur dioxide to sulphur trioxide
catalyst: V₂O₅ (vanadium (V) oxide)
95% of reactants converted


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