What is the destined extent of decomposition for molecules, given infinite time?

Imagining a vacuum-sealed chamber free of cosmic rays, temperature gradients, or other forms of energy input, what would be the destiny of a single molecule given infinite time to decay?

This could be any molecule, but most interesting are probably the kind of molecules which require input energy to break apart.

What would be the destiny of CO2, given 100 trillion years?

Neutrons supposedly decay into proton + electron + and electron anti-neutrino. So eventually we'd be left with some protons (assuming they don't decay), electrons, and anti-neutrinos.

What I'm interested in is this: what causes the various stages of decay to occur, and in what order?

Would the CO2 spontanously break into O2 and C, or would these building blocks themselves decay while in the CO2 formation?

And what would cause a neutron to spontaneously decay without energy input?