Types of Chemical Reactions: Quick Revision

A brief note on Types of Chemical Reactions. Read it before a test. Try each question at the end before you open its answer.

Four types

Decomposition needs heat, light or electricity.

The reactivity series

K, Na, Ca, Mg, Al, Zn, Fe, Pb, (H), Cu, Hg, Ag, Au. A metal displaces only the metals below it.

Oxidation and reduction

• Oxidation: gain of oxygen or loss of hydrogen. Reduction: loss of oxygen or gain of hydrogen.
• They happen together, in a redox reaction.
• The oxidising agent is itself reduced; the reducing agent is itself oxidised.

A worked example

Zinc is put in silver nitrate solution: $\text{Zn} + 2\text{AgNO}_3 \rightarrow \text{Zn(NO}_3)_2 + 2\text{Ag}$. Name the type, and find the silver from $6.5\ \text{g}$ of zinc. Use $\text{Zn} = 65$ and $\text{Ag} = 108$.

1. Type. Zinc is above silver, so it displaces it: a displacement.
2. Moles of zinc. $\dfrac{6.5\ \text{g}}{65\ \text{g/mol}} = 0.1\ \text{mol}$.
3. Silver. The ratio is $1 : 2$, so $0.2\ \text{mol} \times 108\ \text{g/mol} = 21.6\ \text{g}$.

Practice with new numbers

A program to try

The program checks four pairs of metals against the reactivity series.

Mistakes to avoid

• Calling every swap a displacement. If two compounds swap partners, it is a double displacement.
• Reading the reactivity series upside down. The higher metal displaces the lower one.
• Mixing up the agent and what happens to it. The oxidising agent is reduced.
• Forgetting that oxidation and reduction go together.

Check yourself

1. What type of reaction has the pattern $\text{AB} + \text{CD} \rightarrow \text{AD} + \text{CB}$?

2. Will copper displace silver from silver nitrate solution?

3. In $\text{CuO} + \text{CO} \rightarrow \text{Cu} + \text{CO}_2$, which substance is the reducing agent?

4. Name a decomposition that is caused by heat.