Question

How do we address mass and charge in a `"single displacement reaction"`?

Answer 1

You account for them.....

Explanation:

All chemical equations are balanced with respect to (i) mass, and (ii) charge....

And so in a `"single-displacement reaction"` a reactive element typically displaces a less reactive element, which we could represent by the reaction........

`A + B-X rarr A-X + B`

And so for an actual reaction, CHARGE is conserved......neutral reactants give neutral products......and charged reactants give products of equal charge........

`Fe+Cu^(2+)rarrFe^(2+) + Cu`

In the given reaction, which of course is a redox reaction, of course the cations are present as the counterions of some anion that gives soluble salts, but this is the province of experiment.

And so charge is conserved as well as mass. Is it conserved in the iron/copper couple?

Note that when I say `"account for them"` with reference to electric charge, I mean precisely that. If you work in accounting or finance, there is an old saying that goes......

`"....for every credit, there must be a corresponding debit"` or `"Rob Peter, pay Paul"`.

So if you credit one account, you must DEBIT another. At the end of the day when an accountant (so-calls) reconciles his/her account, if the debits DO NOT MATCH the credits precisely, SOMEONE, the client or the bank, is out of pocket.

Chemistry follows the same principle, which of course is the principle of stoichiometry, `"garbage in equals garbage out"`. Of course chemists deal with vaster greater numerically sums and use `"Avogadro's number"` in their accounts.