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Peter Atkins says

In introductory chemistry, we meet the empirical rule of thumb known as Le Chatelier’s principle:

When a system at equilibrium is subjected to a disturbance, the composition of the system adjusts so as to tend to minimize the effect of the disturbance.

For instance, if a system is compressed, then the equilibrium position can be expected to shift in the direction that leads to a reduction in the number of molecules in the gas phase, for that tends to minimize the effect of compression.Le Chatelier’s principle, though, is only a rule of thumb, and to understand why reactions respond as they do, and to calculate the new equilibrium composition, we need to use thermodynamics.

That Le Chatelier’s principle, is only a rule of thumb, and thermodynamic calculations need to be done to determine new equilibria.

So are there any exceptions to this rule of thumb ??


marked as duplicate by Karsten Theis, Jon Custer, Buttonwood, Tyberius, Mithoron Jun 25 at 23:25

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    $\begingroup$ Metastable systems, where the 'disturbance' pushes it over the edge towards a global minimum energy, won't obey it particularly well. $\endgroup$ – Jon Custer Jun 25 at 13:39
  • $\begingroup$ I'll say if you find an exception to Le Chatelier, a closer look will show that you've had a wrong idea (i.e. not the whole picture) about what's actually happening. Very strong hint that you should have a closer look. $\endgroup$ – Karl Jun 25 at 22:02