5.0 Chemical Properties

Hydrogen is less reactive at room temperature because of high bond dissociation energy ($436\ kJ\ mol^{-1}$) due to smaller bond length.

1. It forms compounds with almost all elements (except noble gases $Fe$, $CO$ etc.) under suitable conditions.

$$2Na + {H_2}\mathop \to \limits^{537K} 2NaH$$$$2{H_2} + {O_2}\mathop \to \limits^{970K} 2{H_2}O$$$${H_2} + {F_2}\mathop \to \limits^{dark} 2HF\left( l \right)$$

2. Hydrogen reacts with $CO$ at $700\ K$ under pressure in the presence of catalyst to form methanol. $$CO + 2{H_2}\mathop \to \limits_{Zno/C{r_2}{O_3}}^{700K,200atm} C{H_3}OH$$

3. Hydrogen acts as a reducing agent. $$CuO + {H_2} \to Cu + {H_2}O$$

4. Unsaturated hydrocarbons add dihydrogen in presence of a catalyst to form hydrocarbons. $$C{H_2} = C{H_2} + {H_2} \to C{H_3} - C{H_3}$$

5. Reactions with metal ions and metal oxides: It reduces some metal ions in aqueous solution and oxides of metals (less active than iron) into corresponding metals. $${H_2}\left( g \right) + P{d^{2 + }}\left( {aq} \right) \to Pd\left( s \right) + 2{H^ + }$$