Group VII Displacement Reactions | Chemistry for Grade 11 (IGCSE) PDF Download

Group VII Displacement Reactions

• A halogen displacement reaction occurs when a more reactive halogen displaces a less reactive halogen from an aqueous solution of its halide. This means that a halogen higher in the reactivity series can displace a halogen lower in the series from a solution of its salt. For instance, chlorine can displace bromine from a solution of sodium bromide:
• The reactivity of Group VII non-metals increases as you move up the group. This means that elements higher in Group VII are more reactive than those lower in the group. For example, chlorine is more reactive than bromine or iodine.
• Out of the three commonly used halogens, chlorine, bromine, and iodine, chlorine is the most reactive, while iodine is the least reactive. This reactivity trend is important to consider in various chemical reactions and applications.

Colour of Halogens in Aqueous Solutions

Halogen displacement reactions

• Mixing chlorine solution with a clear potassium bromide solution results in the solution turning orange due to the formation of bromine.
• Chlorine, positioned above bromine in Group VII, exhibits greater reactivity.
• Consequently, chlorine displaces bromine from an aqueous solution of the bromide metal.
• The halogen with the lower reactivity level typically ends up in its elemental state.
  potassium bromide + chlorine  →  potassium chloride + bromine
  2KBr (aq) + Cl₂ (aq) → 2KCl (aq) + Br₂ (aq)

Bromine and Iodine

• Bromine, positioned higher than iodine in Group VII, displays higher reactivity.
• Consequently, bromine displaces iodine from an aqueous solution of metal iodide.
• The solution changes color to brown as iodine is produced.
  magnesium iodide bromine → magnesium bromide iodine
  MgI₂ (aq) Br₂ (aq) → MgBr₂ (aq) I₂ (aq)

Summary table of displacement reactions