IIT JEE , AIEEE Forum - Chemistry , Physical Chemistry - Kc for a reaction increases with increase in temprature but not for thIS REACTION

Kailash_chandra

2NO + O2= 2NO2

WHY?

priyesh

hi

value of equilibrium constant does not always increase with increase in temp

value of equilibrium constant increases with increase in temp only when reaction is endothermic

& it will decrease with increase in temp if the reaction is exothermic

now ur reaction

i.e

2NO + O2= 2NO2is exothermic & hence with increase in temp the equilibrium constant decreases.

catch_arnnie

the only reason i can think of is that the reaction might be endothermic in the backward direction so, Kc does not increase on increase in temperature...

plz correct me if i'm wrong...

iitkgp_bipin

Relationship between equilibrium constant K, standard heat of reaction

H₀ and temperature T is :

ln(K₂/K₁) = (-

H₀/R)(1/T₂ - 1/T₁)

If the reaction is endothermic

H₀ > 0, hence K increases with the increase in temperature.

If the reaction is exothermic,

H₀ < 0, hence K decreases with the increase in temperature.

priyesh

hey bipin sir the equation u have written is wrong(as u have got an extra - sign) & thus the result u have obtined is also wrong(just the opposite to actual)

see

ln(K2/K1) = -

H(1/T2 - 1/T1)

now taking - sign out from

(1/T2 - 1/T1) the two - sign get canceled & we get

ln(K2/K1) = H(1/T1 - 1/T2)

ln(K2/K1) =

H((T2 - T1)/T1T2)

hence if reaction is endothermic then increase in temp will increase the equilibrium constant

& if reaction is exothermic the equilibrium constant decreases with increase in temp

Cheers

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