Combustion basics — heat effects of oxidation The reaction between oxygen and typical organic materials (combustion/oxidation) is generally classified as which type of thermal reaction?

Introduction / Context:
Combustion of organic matter (hydrocarbons, biomass) with oxygen releases energy that is harnessed in furnaces, engines, and power plants. Understanding the sign of heat of reaction is fundamental to reactor design and safety.

Given Data / Assumptions:

• Complete or partial oxidation of organic compounds by O2 is considered.
• Standard enthalpies of formation for CO2 and H2O are highly negative compared to reactants.

Concept / Approach:
Oxidation of reduced carbon and hydrogen to CO2 and H2O lowers chemical potential energy and liberates heat. Therefore, the process is exothermic (ΔH < 0). Even partial oxidation (to CO) is exothermic, though less so than complete combustion.

Step-by-Step Solution:
Compare product vs reactant enthalpies of formation → products are more stable.Hence ΔHreaction is negative, meaning heat release.Classify reaction type as exothermic.

Verification / Alternative check:
Practical observation: flames and hot flue gases accompany combustion; furnaces deliver thermal duty from released heat.

Why Other Options Are Wrong:

• Endothermic: opposite sign; does not describe combustion.
• Biochemical/Photochemical: categories of mechanism/activation source, not the heat effect for ordinary burning.

Common Pitfalls:

• Confusing special oxidative processes (e.g., catalytic partial oxidation) with the general heat effect, which remains exothermic.

Final Answer:
Exothermic