Coal gasification chemistry: For the reaction C + H2O → CO + H2 (steam–carbon reaction), classify the thermal nature of this gasification step.

Introduction / Context:
The steam–carbon reaction (also called the “water–gas reaction”) is a key step in coal gasification and coke/char gasification. It produces synthesis gas components (CO and H2) that are foundational for fuels and chemicals.

Given Data / Assumptions:

• Reaction: C (solid) + H2O (steam) → CO + H2.
• Occurs at elevated temperatures (typically > 800°C) to achieve practical rates.
• No external oxygen is included in this specific step.

Concept / Approach:

The reaction is thermodynamically endothermic; it consumes heat. In industrial gasifiers, heat can be supplied by partial oxidation (exothermic C + O2 → CO2/CO) or by external heating. Heat balance determines temperature profiles and product composition.

Step-by-Step Solution:

Verification / Alternative check:

Process models and enthalpy data show positive heat of reaction for the water–gas reaction; temperatures drop if heat is not supplied.

Why Other Options Are Wrong:

Exothermic: Opposite of the actual heat effect. Catalytic/autocatalytic: Catalysts may enhance rates in some systems, but the intrinsic thermal effect remains endothermic.

Common Pitfalls:

Confusing this reaction with the exothermic water–gas shift (CO + H2O → CO2 + H2) or with partial oxidation reactions.

Final Answer:

Endothermic