Which of the following reactions is endothermic?

Question

1. Burning coal.
2. Magnesium reacting with hydrochloric acid.
3. Thermal decomposition of calcium carbonate.
Combustion of methane.

Answer 1

The endothermic reaction is the thermal decomposition of calcium carbonate. This is because energy is required to break the bonds between the calcium, carbon, and oxygen atoms in the compound, which absorbs heat from the surroundings. The other reactions listed are exothermic, meaning they release heat into the surroundings.