Question

Limestone does NOT decompose when heated to 900K because at 900K, ΔH is:

a. Positive
b. Negative
c. Zero
d. Exothermic

Answer 1

The decomposition of limestone (calcium carbonate) is an endothermic process, requiring the absorption of energy, resulting in a positive ΔH when heated to 900K.

Step-by-step explanation:

The student's question refers to the decomposition of limestone when heated to 900K and what the sign of the ΔH would be. It is known that during an endothermic reaction, energy is absorbed from the surroundings, and the heat of reaction (ΔH) is written as positive because the reaction requires the input of heat to proceed. This can be observed in the thermal decomposition of calcium carbonate (limestone).

For limestone, the decomposition reaction is as follows:

CaCO3 (s) +177.8 kJ → CaO (s) + CO₂(g)

Here, 177.8 kJ is written as a reactant, indicating that it is absorbed by the system. Thus, the ΔH for the decomposition of limestone at 900K would be positive, as it is an endothermic process.