Characteristic reactions of halogens

CHARACTERISTIC REACTIONS OF HALOGENS

With hydrogen:

All the halogens combine directly with hydrogen under different conditions to give hydrogen halides. The reaction with F2 is quite vigorous, Cl2 reacts only in the presence of light, Br2 reacts readily iodine reacts reversibly.
\[H_{2}\; + \;X_{2}\; \rightarrow \; 2HX\]
\[H_{2}\; + \;I_{2}\; \rightarrow \; 2HI\]

With other elements:

• Some elements ignite spontaneously in gaseous F2 at room temperature i.e ( K, B, Si, P, S, I)
• Cl2 reacts with both metals and non-metals except carbon, N2, and O2.
• Br2 is a very reactive element it combines with alkali metals and reacts spontaneously with P, As, Sb.
• I2 is less reactive than Br2 it combines directly with many elements e.g. Ag, Au, Al forming iodides.

Consider the following reactions of halogens with metals.
\[2Fe\; + \;3F_{2}\; \rightarrow \; 2FeF_{3}\]
\[2Fe\; + \;3Cl_{2}\; \rightarrow \; 2FeCl_{3}\]
\[Fe\; + \;Cl_{2}\; \rightarrow \; FeCl_{2}\]

Reaction with water:

F2 has strong affinity for water and decompose water to give HF due to high hydration energy.
\[F_{2}\; + \;2H_{2}O\; \rightarrow \; 4HF\; +\; O_{2}\]
\[3F_{2}\; + \;3H_{2}O\; \rightarrow \; 6HF\; +\; O_{3}\]

Cl2 and to a lesser extent Br2 reacts with H2O to give a mixture of acids.
\[Cl_{2}\; + \;H_{2}O\; \rightarrow \; HCl\; +\; HClO\]
\[2Br_{2}\; + \;H_{2}O\; \rightarrow \; 4HBr\; +\; O_{2}\]

I2 does not react with water due to high lattice energy.

Disproportional Reactions:

Those reaction in which same compound is oxidized and reduced called as disproportional reaction.

Cl2, Br2, I2 form a number of oxyacids in aqueous solutions. The halogen disproportional reactions to form hydrochloric acid and hypohalous acids in water.
\[X_{2}\; + \; H_{2}O\; \rightarrow \; HX^{-1}\; +\; HOX^{+1}\]
\[Cl_{2}\; + \; H_{2}O\; \rightarrow \; HCl^{-1}\; +\; HOCl^{+1}\]
\[Cl_{2}\; + \; 2OH^{-1}\; \rightarrow \; Cl^{-1}\; +\; ClO^{-1}\; +\; H_{2}O\]

Reactions with alkalides:

\[2F_{2}\; + \; 4NaOH\; \rightarrow \; 2NaF\; +\; OF_{2}\; +\; H_{2}O\]
But with more concentrated Alkali
\[2F_{2}\; + \; 4NaOH\; \rightarrow \; 4NaF\; +\; 2H_{2}O \; + \; O_{2}\]

In cold state:-

\[X_{2}\; + \; 2NaOH\; \rightarrow \; NaX\; +\; NaXO \; + \; H_{2}O\]
In hot state:-

\[X_{2}\; + \; 6NaOH\; \rightarrow \; 5NaX\; +\; NaXO_{3} \; + \; 3H_{2}O\]

Reaction with Hydrogen sulphide:

\[X_{2}\; + \; H_{2}S\; \rightarrow \; 2HX\; +\; S\]
With all X2 (Halogens)
\[Cl_{2}\; + \; H_{2}S\; \rightarrow \; 2HCl\; +\; S\]