Question: are all reactions reversible?

Alexander Henderson answered on 11 Mar 2015:

Technically, yes; in reality, no. Let’s consider the combustion of methane (CH4). CH4 + 2 O2 -> 2 H2O + CO2. The products are far lower in energy than the starting materials and the “equilibrium” lies far on the right hand side. Theoretically, if you could apply the energy to reduce CO2 with H2O you could perform the reverse reaction, however the relative energies required are massive. Reactions where there is a large energy difference between reactants and products we can essentially think of being irreversible.