reversible reaction

reversible reaction

Chemical reaction that proceeds in both directions at the same time, as the product decomposes back into reactants as it is being produced. Such reactions do not run to completion, provided that no substance leaves the system. Examples include the manufacture of ammonia from hydrogen and nitrogen, and the oxidation of sulphur dioxide to sulphur trioxide.

N2 + 3H2 ⇌ 2NH3

2SO2 + O2 ⇌ 2SO3

The term is also applied to those reactions that can be made to go in the opposite direction by changing the conditions, but these run to completion because some of the substances escape from the reaction. Examples are the decomposition of calcium hydrogencarbonate on heating and the loss of water of crystallization by copper(II) sulphate pentahydrate.

Ca(HCO3)2(aq) → CaCO3(s) + CO2(g) + H2O(l)

CuSO4.5H2O(s) → CuSO4(s) + 5H2O(g)