A small change in ΔG makes a big difference in K
المؤلف:
Jonathan Clayden , Nick Greeves , Stuart Warren
المصدر:
ORGANIC CHEMISTRY
الجزء والصفحة:
ص244
2025-05-15
604
The tiny difference in energy between the hydrate and the aldehyde (1.7 kJ mol−1 is small: the strength of a typical C–C bond is about 350 kJ mol−1) gave an appreciable difference in the equilibrium composition. This is because of the logarithm term in the equation ΔG = –RTlnK: relatively small energy differences have a very large effect on K. The table below shows the equilibrium constants, K, that correspond to energy differences, ΔG, between 0 and 50 kJ mol−1. These are relatively small energy differences, but the equilibrium constants change by enormous amounts.
In a typical chemical reaction, ‘driving an equilibrium over to products might mean getting, say, 98% of the products and only 2% of starting materials. You can see in the table that this requires an equilibrium constant of just over 50 and an energy difference of only 10 kJ mol−1. This small energy difference is quite enough—after all, a yield of 98% is rather good!
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