How does pH affect the spontaneity of biochemical processes? A decrease in $\mathrm{pH}$ increases the hydrogen ion concentration, thereby decreasing $Q,$ and decreasing Gibbs free energy as mathematically expressed:
$$\mathrm dG =\mathrm dG^\circ + RT\ln Q$$
This means that the more acidic the environment is, the more spontaneous the reaction is. But don't biochemical processes operate at approximately neutral $\mathrm{pH} = 7,$ so enzymes function optimally (does not denature)? But why does the equation favor spontaneity at (for example) $\mathrm{pH} = 3$ than $\mathrm{pH} = 7?$
For specific case, such as the biological oxidation of ethanol? Does it mean that it will thrive at acidic environment based on the equation? But how can we explain for the specificity of biological reaction operating at their optimal pH ranges?
For example, in the stomach it requires an acidic environment so the equation holds true. But what about for other biochemical processes that operate at neutral pH (the equation cannot explain it)? Or is there actually another equation to utilize to explain how spontaneous biochemical reactions can be?
Note that pH effect is reaction specific.
If a reaction is e.g. $\ce{A + B + H+ &lt;=&gt; C + D+}$ , or $\ce{A + B- &lt;=&gt; C + D + OH−}$,
then lowering pH supports the spontaneity.
If OTOH, the reaction is $\ce{A + B + OH-  &lt;=&gt; C + D−}$ , or $\ce{A + B+ &lt;=&gt; C + D + H+}$,
then lowering pH goes against the spontaneity.
It can be generalized by applying the Le Chatelier's principle, saying systems adapts to external changes by such equilibrium shifts that partially decreases the system chage caused by the external factor.
Lowering pH supports spontaneity of reactions consuming H+ and vice versa.
Increasing temperature prefers endothermic reactions consuming heat and vice versa.
Increasing pressure prefers reactions decreasing the total molar amount of gaseous components and vice versa.

Note that biological systems are much more complex than chemical systems.
Lowering pH may support thermodynamic spontaneity of some particular reaction. But an enzyme catalyzing its kinetic rate may start loosing its activity, get denatured, cells may stop producing the enzym, cells may stop overall life functions, or may die.