Halogen Displacement Reactions Flashcards

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What is a halogen displacement reaction?

It is a reaction where a more reactive halogen takes the place of a less reactive halogen from a solution of its salt.

How does reactivity change as you go down Group 7 (the halogens)?

Reactivity decreases down the group: chlorine is more reactive than bromine, and bromine is more reactive than iodine.

What is a halide ion? Give two examples.

A halide ion is a negative ion made from a halogen, for example chloride (Cl-), bromide (Br-) or iodide (I-).

State the rule for deciding if a displacement reaction will happen between two halogens.

A displacement reaction happens only if the halogen you add is more reactive than the halogen in the salt solution.

What are the products when chlorine water is added to potassium bromide solution, and what colour change is seen?

Chlorine displaces bromine to form potassium chloride and bromine; the colourless solution turns orange or brown.

What are the products when chlorine water is added to potassium iodide solution, and what colour change is seen?

Chlorine displaces iodine to form potassium chloride and iodine; the colourless solution turns brown.

What are the products when bromine water is added to potassium iodide solution, and what colour change is seen?

Bromine displaces iodine to form potassium bromide and iodine; the solution changes from orange to brown.

What happens when iodine solution is added to potassium chloride solution, and why?

No reaction happens and the colour does not change, because iodine is less reactive than chlorine and cannot displace it.

How can you use halogen displacement reactions to put chlorine, bromine and iodine in order of reactivity?

See which halogens can displace others from their salt solutions: the one that displaces the most is most reactive, and the one never displaced is least reactive.

Write a balanced symbol equation, with state symbols, for the reaction between chlorine water and potassium bromide solution.

Cl2(aq) + 2KBr(aq) → 2KCl(aq) + Br2(aq).

Why do halogens become less reactive as you go down Group 7?

Going down the group, atoms have more electron shells, so the outer shell is further from the nucleus and gains an extra electron less easily, making the halogen less reactive.

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