joule per mole

The joule per mole is the size of the gas constant, and that is where a reader actually meets it: $R = 8.314$ J/(mol·K), so RT at 25 °C is about 2478 J/mol. Thermodynamics keeps wanting that product, in Boltzmann factors, in the Nernst equation, in the barometric formula, and J/mol is the scale on which RT stays a comfortable four-digit number. The Arrhenius and Gibbs solvers on this site take their energies in this unit's kilo-multiple, and the factor of 1000 between the two is the working conversion.

Bare J/mol, without the kilo, is the right size only for the feeblest interactions chemistry knows. The benchmark is the helium dimer, the weakest bound molecule ever observed: its well depth is about 90 J/mol, a small fraction of room-temperature RT, which is why the molecule survives only in beams cooled to well below a kelvin. Anything a chemist would call a bond is a thousand times bigger, and that gap is the whole reason the kilojoule per mole took over everyday reporting.

The trap is the split convention that follows. Enthalpies arrive in kJ/mol while entropies stay in J/(mol·K), so the TΔS term of a Gibbs calculation emerges in J/mol and must lose three zeros before it meets ΔH. Missed, the mismatch flips a reaction's predicted direction, which is why this catalog warns about it on more than one page.