Question

Do either of the following reactions go to completion? If so, what factor(s) cause(s) each to do so?

1. ${\mathrm{MgSO}}_3\left(\mathrm{s}\right)+2\mathrm{HCI}\left(\mathrm{aq}\right)\to {\mathrm{MgCI}}_2\left(\mathrm{aq}\right)+{\mathrm{SO}}_2\left(\mathrm{g}\right)+{\mathrm{H}}_2\mathrm{O}$
2. $3\mathrm{Ba}{\left(\mathrm{OH}\right)}_2\left(\mathrm{aq}\right)+2{\mathrm{H}}_3{\mathrm{PO}}_4\left(\mathrm{aq}\right)\to {\mathrm{Ba}}_3{\left({\mathrm{PO}}_4\right)}_2\left(\mathrm{s}\right)+6{\mathrm{H}}_2\mathrm{O}\left(\mathrm{I}\right)$

Short answer

Answer

(a) ${\mathrm{MgSO}}_3\left(\mathrm{s}\right)+2\mathrm{HCI}\left(\mathrm{aq}\right)\to {\mathrm{MgCI}}_2\left(\mathrm{aq}\right)+{\mathrm{SO}}_2\left(\mathrm{g}\right)+{\mathrm{H}}_2\mathrm{O}$

This reaction goes to completion.

(b) $3\mathrm{Ba}{\left(\mathrm{OH}\right)}_2\left(\mathrm{aq}\right)+2{\mathrm{H}}_3{\mathrm{PO}}_4\left(\mathrm{aq}\right)\to {\mathrm{Ba}}_3{\left({\mathrm{PO}}_4\right)}_2\left(\mathrm{s}\right)+6{\mathrm{H}}_2\mathrm{O}\left(\mathrm{I}\right)$

This reaction goes to completion

Step-by-step solution

Determine the situation of the completion of the reaction

If the reaction is irreversible and all the reactants are consumed in the reaction then the reaction becomes complete.

Determine factors which causes completion of the reaction

${\mathrm{MgSO}}_3\left(\mathrm{s}\right)+2\mathrm{HCI}\left(\mathrm{aq}\right)\to {\mathrm{MgCI}}_2\left(\mathrm{aq}\right)+{\mathrm{SO}}_2\left(\mathrm{g}\right)+{\mathrm{H}}_2\mathrm{O}$

In the above reaction, sulphur dioxide ${\mathrm{SO}}_2$ is formed which can escape from the system and water is formed. Hence the reaction is irreversible which means the reaction goes to completion.

(b)The formation of a precipitate makes the backward reaction impossible. Apart from that water is also formed which is a non -electrolyte. Therefore, the reaction cannot go to completion.