Question

Which of the following reactions are endothermic?

A. CaCO3 --> CaO + CO2 ΔH=+178kJΔH=+178kJ
B. Mg + O2 --> MgO ΔH=−602kJΔH=−602kJ
C. AgCl(s) + Heat --> Ag+(aq) + Cl- (aq)
D. CH4 + 2O2 --> CO2 + 2H2O + Heat

Answer 1

Reaction A (CaCO3 decomposition) and Reaction C (AgCl dissolution with heat) are endothermic, while Reaction B (Magnesium oxidation) and Reaction D (Methane combustion) are exothermic.

Step-by-step explanation:

The question pertains to identifying which of the listed chemical reactions are endothermic reactions. An endothermic reaction is characterized by the absorption of energy from the surroundings, which is indicated by a positive enthalpy change (ΔH). Based on the provided reactions:

• Reaction A (CaCO3 --> CaO + CO2 ΔH=+178kJ) is endothermic since it absorbs energy (ΔH is positive).
• Reaction C (AgCl(s) + Heat --> Ag+(aq) + Cl- (aq)) is also endothermic because it requires the addition of heat as a reactant to proceed.

On the contrary:

• Reaction B (Mg + O2 --> MgO ΔH=−602kJ) and Reaction D (CH4 + 2O2 --> CO2 + 2H2O + Heat) are both exothermic, as they release energy (ΔH is negative).