Under what conditions can hydrogen be made to combine with

(a) nitrogen

(b) chlorine

(c) sulphur

(d) oxygen

Name the products in each case and write the equation for each reaction.

(a) Three volumes of hydrogen and one volume of nitrogen react at temperature 450-500°C, pressure 200-900 atm in the presence of a catalyst, finely divided iron, with molybdenum as a promoter to give ammonia.

$\text{N}$2 + 3\text{H}2 \xrightleftharpoons[\text{450-500 \degree C}]{\text{Fe}} \text{2NH}_3 + \Delta

(b) Equal volumes of hydrogen and chlorine react slowly in diffused sunlight but explosively in direct sunlight, to form hydrogen chloride.

$\text{H}$2 + \text{Cl}2 \xrightarrow{\text{sunlight}} 2\text{HCl}

(c) Hydrogen gas on passing through molten sulphur reacts to give hydrogen sulphide.

$\text{H}$2 + \underset{\text{molten sulphur}}{\text{S}} \longrightarrow \text{H}2\text{S}

(d) Hydrogen burns (in presence of electric spark) with a 'pop' sound in oxygen and with a blue flame forming water.

$2\text{H}$2 + \text{O}2 \xrightarrow{\text{electric spark}} 2\text{H}_2\text{O}