From moles to reactions

0.50 mol contains 3.01107038 × 10^23 specified entities because the Avogadro constant is exact.

For 2 H2 + O2 → 2 H2O, two moles of hydrogen react with one mole of oxygen in the balanced ideal ratio.

Combustion releases energy to the surroundings; at constant pressure this is described by a negative enthalpy change.