How are chemical formulae of different compounds represented?

Jun 12, 2017

Is that all you want? We could be here for days!

Explanation:

Chemical symbols, $H$, $H e$, $C$, $N$, $O$ $e t c .$ describe the 100 or so known elements, which, as far as chemists know, constitute all matter. The elements are systematically grouped in the Periodic Table.

Chemical formulae represent the combinations of atoms to give molecules and compounds of different elements, e.g. ${H}_{2}$, $C {H}_{4}$, $C {O}_{2}$, ${C}_{6} {H}_{12} {O}_{6}$.

And chemical equations are a simple shorthand means to represent how elements and compounds chemically interact to form new compounds and materials. A typical chemical reaction is the combustion of methane gas with dioxygen, the which underlies our industrial civilization:

$C {H}_{4} \left(g\right) + 2 {O}_{2} \left(g\right) \rightarrow C {O}_{2} \left(g\right) + 2 {H}_{2} O \left(l\right) + \Delta$

Using the known masses of (given quantities) of elements we can thus use the given equation to represent mass and energy transfer: i.e. $16 \cdot g$ $\text{methane}$ is combusted by $64 \cdot g$ of $\text{dioxygen}$ to give $44 \cdot g$ $\text{carbon dioxide}$ and $36 \cdot g$ of water. Such a combustion also results in a measurable energy transfer, and such energy (here represented by the symbol $\Delta$) can be used to do useful work. Both mass and energy may thus be quantitatively assessed by such chemical equations.

All known chemical reactions CONSERVE mass and CONSERVE energy. What does this mean in the given context?