Question

Hi Friends ....
Good Morning....

can you please answer this question :-

For the reaction H2(g) + I2 (g) <-------> 2HI (g)
Equilibrium constant , Kc = 49 . What would be the value of the equilibrium constant for
1/2 H2 (g) + 1/2 I2 (g) <--------> HI(g) . UUnder the same conditions ?

Thank You ,
^_^

Answer 1

Hello Anaida^_^

You could solve this problem by writing down the rate expression...or the easier way is to have an idea on some general points...Which i'll mention below.

First Let's get into the answer...

1) For any given reaction...If any reaction is multiplied by a factor n then the value of equilibrium constant becomes (Kc)^n ..

And in this case...Reaction is multiplied by 1/2...So the equilibrium constant becomes (49)^1/2 which means sqaure root of 49 which is equal to 7.

So the answer of this question is 7.

Anaida...Now let's have a look into some general points apart from the one we solved just now.....So that.. We could  easily solve similar types of questions..

2) if the reaction is reversed....the value of equilibrium constant is reciprocated..Which means it become 1/ Kc...Taking " Kc" is the equilibrium constant before the reaction is reversed.

A+B -------> C +D ...For this...Let Equilibrium constant be " Kc"

So..For C+D -------> A+ B...After reversing...Equilibrium constant becomes 1/Kc...(We take the reciprocal)

And now taking another example...Using  Our first point which we used to solve the question..

A+ B  ------->2C.....Let equilibrium constant be " Kc"

Then For 2A + 2B -------> 4C....Equilibrium constant becomes "2 *Kc"...

As here the reaction is multiplied by 2 we'll do the same with the equilibrium constant too..

3)If a reaction is completed in more than one steps....And if K1, K2, K3, Etc....are equilibrium constants of each step.....Then the equilibrium constant of overall reaction is the product of equilibrium constant of each step....So for overall reaction Equilibrium constant Kc would be eqaul to K1 x  K2 x K3 x K4.x....

4)Keep in mind that While calculating Kc we don't consider solids and liquids...We only do consider gases.

So using the above points...We could solve majority of these types of questions