How would you describe the change of wood when it is burning

When wood is burning, it undergoes a complex series of physical and chemical transformations. Here’s a breakdown of the key changes that occur:

1. **Heating Phase**: Initially, as the wood is heated, it loses moisture. This process can produce steam and other volatile compounds. The temperature continues to rise as the wood is exposed to flame or high heat.

2. **Pyrolysis**: As temperatures increase (typically between 200°C and 300°C or 392°F and 572°F), the wood undergoes pyrolysis, a thermal decomposition process. This produces gases, tars, and charcoal as the cellulose, hemicellulose, and lignin within the wood break down. The gaseous products can include water vapor, carbon dioxide, carbon monoxide, and various volatile organic compounds.

3. **Combustion**: When the volatile gases released during pyrolysis ignite, they produce flames. The combustion process is a rapid chemical reaction with oxygen that generates heat, light, carbon dioxide, and water vapor. As the wood continues to burn, the solid structure is consumed.

4. **Char Formation**: After the volatile components are burned off, what remains is charcoal, which is primarily carbon. This char can continue to burn slowly if oxygen is available, producing heat but minimal light.

5. **Ash Formation**: Eventually, as the burning process progresses, the remaining inorganic materials in the wood (such as minerals) are left behind as ash. This ash consists of various compounds, often including calcium, potassium, magnesium, and phosphorus.

6. **Heat and Light Emission**: Throughout this process, significant heat and light are emitted, contributing to the warmth and illumination associated with fire.

In summary, as wood burns, it transitions from a solid state to gases, light, and ash, driven by processes of dehydration, pyrolysis, combustion, and finally, residual ash formation. Each stage is characterized by physical changes (like smoke and heat) and chemical changes (like the breakdown of organic compounds and combustion reactions).