Quantitatively,
however, a chemical equation does not tell us what we have; the
coefficients are conditional statements regarding the proportion of chemical
substances involved.
For example, the
following equation
–2H2 (g) + O2 (g) ¾® 2H2O (g)
says if
two moles of hydrogen gas were combined with one mole of oxygen gas,
then two moles of steam will be produced.
Similarly,
–CaCO3 (s) ¾® CaO (s) + CO2 (g)
if 1 mole
of CaCO3 were heated, then one
mole each of CaO and CO2 would be produced.
And,
–2Mg (s) + O2 (s) ¾® 2MgO (s)