What is the chemical process called when heat causes wood molecules to change during combustion?

The correct answer is pyrolysis, which is the chemical process that occurs when heat is applied to wood, causing it to decompose in the absence of oxygen. During pyrolysis, complex organic molecules in the wood break down into simpler compounds, releasing volatile gases, water vapor, and leaving behind char. This transformation is essential for combustion because it prepares the wood for burning by converting it into flammable gases.

Pyrolysis is a critical step that occurs before the actual combustion process, as it generates the combustibles that will later undergo oxidation in the presence of oxygen to produce flames and heat. Understanding pyrolysis is vital in the context of fireplace and wood-burning technology, as it influences how efficiently a fire burns and the types of emissions produced.

In contrast, carbonization refers to the decomposition of organic material through heat, but it specifically results in a solid residue that is primarily carbon, like charcoal, and is not the direct process occurring in the initial stages of wood combustion. Oxidation is the chemical reaction that occurs during the burning of the gases produced from pyrolysis, while fermentation is a biological process involving the breakdown of sugars by microorganisms and does not relate directly to wood combustion.