Chemistry: why a reaction proceeds from left to right
The tutor explains why a reaction goes forward.
Consider, from my previous post, the following reaction:
C3H8 + 5O2→3CO2+4H20, ΔH=-2219 kJ/mol
This reaction proceeds from left to right because, by so doing, it follows nature’s two preferred trends:
- Entropy rises (for a definition of entropy, see my post here).
- Enthalpy falls (for a definition of enthalpy, see my post here).
At a glance, the rise in entropy can be noticed by the increase in molecules from left to right (6 to 7). The fall in enthalpy is indicated by the negative ΔH value.
A chemical transformation that produces, simultaneously, a rise in entropy and a fall in enthalpy, will be spontaneous: once started, it will self-sustain.
Source:
Mortimer, Charles E. Chemistry, 6th ed. Belmont: Wadsworth, 1986.
Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.
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