Question

What are the basic reaction types? Explain each with an example.

Answer 1

There are four basic types of reactions. They are:

• Synthesis reaction
• Decomposition reaction
• Simple displacement reaction
• Double displacement reaction

Synthesis reaction:

• The combination or synthesis reaction occurs when two or more elements or compounds combine chemically to form a new product.
• The general representation for this reaction is:

X + Y → XY

• Synthesis reaction could be explained with the following example:

Nitrogen and hydrogen combine to form ammonia.

$\underset{\mathrm{nitrogen}}{{\mathrm{N}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{hydrogen}}{3{\mathrm{H}}_2\left(\mathrm{g}\right)}\to \underset{\mathrm{ammonia}}{2{\mathrm{NH}}_3\left(\mathrm{g}\right)}$

Here, two different elements, nitrogen, and hydrogen combine chemicals, and a new, single product with different properties than the reactants is formed i.e, ammonia.

Decomposition reaction:

• In a decomposition reaction, one chemical substance is decomposed into one or more products.

$\underset{\mathrm{copper}\mathrm{carbonate}}{{\mathrm{CuCO}}_3\left(\mathrm{s}\right)}\to \underset{\mathrm{copper}\mathrm{oxide}}{\mathrm{CuO}\left(\mathrm{s}\right)}+\underset{\mathrm{carbon}\mathrm{dioxide}}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}$

• In the given reaction, copper carbonate(CuCO₃) when heated is decomposed into copper oxide(CuO) and carbon dioxide(CO₂).

Single displacement reaction:

• According to the reactivity series, the metals that come first are more reactive than the ones that are below them.
• More reactive metals can displace less reactive metals from their compounds.
• Single displacement reactions take the form:
  AB + C → A + CB
• Example:

$\underset{\mathrm{zinc}}{\mathrm{Zn}\left(\mathrm{S}\right)}+\underset{\mathrm{copper}\mathrm{sulfate}}{{\mathrm{CuSO}}_4\left(\mathrm{aq}\right)}\to \underset{\mathrm{copper}}{\mathrm{Cu}\left(\mathrm{s}\right)}+\underset{\mathrm{zinc}\mathrm{sulfate}}{{\mathrm{ZnSO}}_4\left(\mathrm{aq}\right)}$

• According to the reactivity series, zinc(Zn) is more reactive than copper(Cu) as zinc comes first in the series.
• When zinc is added to copper sulfate (CuSO₄₎ solution, copper is replaced by zinc and forms zinc sulfate (ZnSO₄).
• The color of the solution changes from blue to colorless during the reaction.

Double displacement reaction:

• A double displacement reaction is a type of reaction in which two reactants exchange ions to form two new compounds.
• Double displacement reactions take the form:
  AB + CD → AD + CB
• Example:

$\underset{\mathrm{Barium}\mathrm{chloride}}{{\mathrm{BaCl}}_2\left(\mathrm{aq}\right)}+\underset{\mathrm{Sodium}\mathrm{sulfate}}{{\mathrm{Na}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)}\to \underset{\mathrm{Barium}\mathrm{sulfate}}{{\mathrm{BaSO}}_4\left(\mathrm{s}\right)}+\underset{\mathrm{Sodium}\mathrm{chloride}}{2\mathrm{NaCl}\left(\mathrm{aq}\right)}$

In the given reaction, chloride ion is acquired by sodium from barium chloride and sulfate ion is taken by barium from sodium chloride.