Question

$\text{Zn + }{{\text{H}}_{2}}\text{S}{{\text{O}}_{4}}(\text{dil})\,\to \text{ ZnS}{{\text{O}}_{4}}\ \text{+ }{{\text{H}}_{2}}\uparrow $
Above reaction is:
A. decomposition reaction
B. displacement reaction
C. combination reaction
D. synthesis reaction

Answer 1

Hint: For this problem we should know about the types of reaction so that the correct option can be selected. Also, we have to study the reactivity series so that the ability of the element to reduce can be determined.

Complete Step-by-Step answer:
- In the given question, we have to choose the correct type of reaction among the given options.
- As we know that any change in the colour, structure or formation of precipitate confirms that the chemical reaction has taken place.
- So, there are many types of reaction depending on the product formed by the reactant.
- Decomposition reactions are those reactions in which the breakdown of the compound takes place into a simpler compound.
- For example, breakdown of hydrogen peroxide into water and oxygen i.e. $\text{2}{{\text{H}}_{2}}{{\text{O}}_{2}}\,\to \text{ 2}{{\text{H}}_{2}}\text{O + }{{\text{O}}_{2}}$.
- Whereas combination reaction is a reaction in which the two simpler molecules combine to form a complex large molecule.
- For example, hydrogen and chlorine combine to form hydrochloric acid i.e. ${{\text{H}}_{2}}\text{ + }\text{C}{{\text{l}}_{2}}\text{ }\to \text{ 2HCl}$
- Synthesis reaction is also a type of combination reaction because in it the synthesis of a compound takes place by the combination of two or more reactants.
- For example, synthesis of calcium hydroxide takes place when calcium oxide and water react with each other i.e.
$\text{2CaO + 2}{{\text{H}}_{2}}\text{O }\to \text{ 2Ca(OH}{{\text{)}}_{2}}$
- Now, the displacement reactions are reactions in which one element displaces the other element if it has more reducing power than it.
- For example, $\text{Zn + }{{\text{H}}_{2}}\text{S}{{\text{O}}_{4}}(\text{dil})\,\to \text{ ZnS}{{\text{O}}_{4}}\ \text{+ }{{\text{H}}_{2}}$ in it, the zinc has more reducing power than the hydrogen that's why it displaces it and forms zinc sulphate.

Therefore, option B is the correct answer.

Note: To compare the reducing power of the different elements, a reactivity is prepared in which the elements present above the hydrogen have most reducing power whereas those which are present below the hydrogen have less reducing power.