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I appreciate Professor Logan calling attention to
his well-crafted article of several years ago. Had I
been aware of it, I would have cited it in my paper. I
welcome the opportunity to reiterate my case against overuse
of the Delta symbol.
Logan and I both find utility in graphs of
G, the free energy of a system, versus x, the extent of a reaction
occurring in the system. The slope of the graph at any
point can be calculated from DGo +
RT lnQ. It determines if the reaction is at equilibrium or if it will proceed in
the forward or backward direction. But, what shall we
call this slope? The mathematically correct symbol is
dG/dx. For students not versed in calculus we can simply
refer to it as "the slope of the tangent" or "the rate of
change of free energy with respect to advancement of the
reaction". It can even be symbolized
Delta G/Delta x. I believe the current practice of simply calling it
Delta G misleads the student. The Delta G symbol should be limited to differences between initial and final states. Instructors who
want to avoid the entire issue can continue to determine
the reaction direction by comparing Q with the
equilibrium constant, K.
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