Why heating of catalyst is discontinued the moment the oxidation of ${\mathrm{SO}}_2$ takes place?

What property of concentrated sulphuric acid is made use of in the following case? Give an equation for the reaction in each case.

Hydrogen sulphide gas is passes through concentrated sulphuric acid.

What property of concentrated sulphuric acid is made use of in the following case? Give an equation for the reaction in each case.

In the preparation of sulphur dioxide by warming a mixture of conc. Sulphuric acid and copper turnings.

What property of concentrated sulphuric acid is made use of in the following case? Give an equation for the reaction in each case.

As a source of hydrogen by diluting it and adding a strip of magnesium.

Complete the following equation:

$\mathrm{Cu} + {\mathrm{H}}_2{\mathrm{SO}}_4(\mathrm{Conc}.) \to$

Complete the following equation:

${\mathrm{H}}_2\mathrm{S} + {\mathrm{H}}_2{\mathrm{SO}}_{4 }\to$

Complete the following equation:

$\mathrm{S} + {\mathrm{H}}_2{\mathrm{SO}}_4 (\mathrm{conc}.) \to$

Complete the following equation:

${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}\stackrel{\mathrm{Conc}.{\mathrm{H}}_2{\mathrm{SO}}_4}{\to }$

Complete the following equation:

${\left(\mathrm{COOH}\right)}_2\stackrel{\mathrm{Conc}.{\mathrm{H}}_2{\mathrm{SO}}_4}{\to }$