Which one of the following reactions is a combination reaction?

The correct answer is Mg(s) + Cl2(g) → Mgcl2(s).

Key Points

• Magnesium (Mg) combines with chlorine (Cl2) to form a new product as magnesium chloride (Mgcl2). Therefore its a combination reaction and the balanced equation can be written as:
  • Mg(s) + Cl2(g) → Mgcl2(s)​

Additional Information

• A combination reaction is a reaction where two or more elements or compounds combine to form a single compound. Such reactions are represented by equations of the following form: X + Y → XY.
• The combination of two or more elements to form one compound is called a combination reaction.
• Other types of Chemical Reactions:
  • Decomposition reaction: The opposite of a combination reaction, a complex molecule breaks down to make simpler ones. Such reactions are represented by equations of the following form: AB → A + B.
  • Precipitation reaction: Two solutions of soluble salts are mixed resulting in an insoluble solid (precipitate) forming. Such reactions are represented by equations of the following form: A + Soluble salt B  → Precipitate + soluble salt C.
  • Neutralization reaction: An acid and a base react with each other. Generally, the product of this reaction is a salt and water. Such reactions are represented by equations of the following form: Acid + Base → Salt + Water.
  • Combustion reaction: Oxygen combines with a compound to form carbon dioxide and water. These reactions are exothermic, meaning they give off heat. Such reactions are represented by equations of the following form: A + O2 → H2O + CO2.
  • Displacement reaction: One element takes place with another element in the compound. Such reactions are represented by equations of the following form: A + BC → AC + B.