Sciencemadness Discussion Board

How to determine which way will it go?

Sulaiman - 25-5-2015 at 02:12

In the thread 'KCL from KNO3' blogfast 25 made the statement;
'The equilibrium for HCl + HNO3 === > NOCl lies much to the left.'

How do I look at a chemical equation and work out which paths are most favourable?

blogfast25 - 25-5-2015 at 05:33

Quote: Originally posted by Sulaiman  
In the thread 'KCL from KNO3' blogfast 25 made the statement;
'The equilibrium for HCl + HNO3 === > NOCl lies much to the left.'

How do I look at a chemical equation and work out which paths are most favourable?


It's not really a question of 'which path'.

Take a simple, generic case:

A < === > B

This is an equilibrium reaction, once equilibrium is achieved A is converted to B and B is also converted back to B, simultaneously. At equilibrium the following condition applies:

K = [B]/[A] with K the equilibrium constant and [A]/[B] the ratio of concentrations of A and B.

If [A] is small and [B] large, then K is large and the equilibrium is said to be left leaning.

If [A] is large and [B] is small then K is small and the equilibrium is said to be right leaning.

The constant K is calculated from ΔG (for A === > B) and Nernst's Derivation.



[Edited on 25-5-2015 by blogfast25]