Question

In: Chemistry

It is known that at 300K the value of Kp for a certain reaction is 10^(12)....

It is known that at 300K the value of Kp for a certain reaction is 10^(12). For the reaction △H is 100kJ/mole.
a.Determine if this reaction is favorable at 800K and estimate Kp(800K). explain
b. The actual value of Kp (800) is 35. Explain any discrepancy from your estimate.

Solutions

Expert Solution

Given and

(a) It is given that the reaction is feasible at 300K. That is according to the Van't Hoff equation , at 300K

so that . With increasing T the becomes much more negative. Hencea t higher temperature, e.g. 800K, the above inequality must holds and the free energy change will negative at this temperature. Therefore at 800K the reaction is feasible.

The temperature dependency of equilibrium constant is given by Van't Hoff isobar

where is the equilibrium constant at temperature and is at temperature . Now it is given that

and .

Therefore

This is the value of the equilibrium constant at 800K.

(b) The actual value of the equilibrium constant is .

Therefore it is observed that, there is a huge difference between the actual value and the value calculated above. This is due to the fact that, in Van't Hoff isobar the enthalpy change is taken to be independent of temperature. In reality this independency does not work well for a huge change in temperature e.g. from 300K to 800K. Hence at 800K must be different from at 300K.

queen_honey_blossom answered 1 year ago

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