Question

Consider the reaction, Ag₂CO₃(s) ↔ Ag₂O(s) + CO₂(g), for which the following data have been reported for the equilibrium constant (K_eq) measured at four different temperatures:

   T =          350 K                 400 K                 450 K                   500 K

    K_eq =      3.98 x 10^-4         1.41 x 10^-2        1.86 x 10^-1           1.48

(a). Does this data indicate that the reaction is endothermic or exothermic? Give a rationale for your answer.

(b). Can this data be used to calculate a value for the ∆_rH^o of the reaction? If you answer Yes, explain how you would go about doing that.

Answer 1

a)

First, analyse the trend as T increases... this implies the system gets more ENERGY

As T increases, Keq increases as well

this implies:

Keq = [Products] / [reactants]

now, as K increases, this implies  [Products] /increases and [reactants] decreases

therefore, this must be ENDOTHERMIC

that is, as we add more energy, the equilibrium favours the products

b)

Yes, this could be done, we must apply vant Hoff equation

it relates:

ln(K) = -H/R*(1/T) + S/R

in which we can fit many data as follows:

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