When wood burns, the mass of the ash is less than the mass of the original wood. Yet the law of conservation of matter says that mass cannot be created or destroyed in a chemical reaction. How do you reconcile the result of burning with this law?

When you strike a match or light a candle, what you're witnessing is a combustion reaction. Combustion is a high-temperature exothermic reaction between a fuel, like wood or gasoline, and an oxidant, often atmospheric oxygen (\( O_2 \)). This type of chemical reaction releases energy in the form of heat and sometimes light, making it a cornerstone in generating power for human use.

Typical Combustion in Daily Life

Everyday examples of combustion include burning wood in a fireplace, igniting fuel in an engine, or cooking with a gas stove. The process always leads to the creation of new substances, termed as the combustion products—which for most organic materials, primarily include carbon dioxide (\( CO_2 \)) and water (\( H_2O \)).

In the specific case of burning wood, the chemical compounds cellulose and lignin react with oxygen, transforming into new compounds while releasing energy. It's a natural misconception to think that matter is lost when we see the wood disappearing into a small pile of ash, but the laws of chemistry explain this seemingly mysterious occurrence.

A chemical reaction is a rearranging of atoms in substances to form different substances. It's like a dance where partners (atoms) switch to create new dancing pairs (molecules). In a chemical reaction, the substances you start with are called reactants, and the new substances formed are called products.

As with any dance, there are certain rules. One of these rules is the law of conservation of matter, which states that in an isolated system, matter is neither created nor destroyed by chemical reactions or physical transformations. Simply put, the number of atoms you have at the beginning is the same number you end up with—they've just been rearranged into different patterns to make new substances.

The conservation of mass is a fundamental concept in chemistry that reflects the efficiency and predictability of the natural world. French chemist Antoine Lavoisier articulated this law, stating that the mass of a closed system must remain constant over time. This principle provides the foundation for balancing chemical equations—ensuring the number of atoms of each element is equal on both sides of the reaction.

When burning wood, we're tempted to think mass has vanished when we observe less ash than the original amount of wood. However, if we could capture and weigh all the combustion products—including the invisible gases like carbon dioxide and water vapor—we would find the total mass to remain unchanged. This emphasizes that the substance of the wood hasn’t been lost; it has transformed and dispersed.

The end result of a combustion reaction are the combustion products. In the burning of wood, the cellulose and lignin that make up most of the wood's structure combine with oxygen to form new products: ash, carbon dioxide, and water vapor. While ash is the visible residue that remains after a fire, it’s easy to overlook the other combustion products because they are gases that disperse into the atmosphere.

The massive trees that once stood are reduced to small amounts of ash because most of their mass has been converted into gas during the combustion process. These gaseous products rise and mix with the atmosphere, which may seem like a loss, but they are simply in a form our eyes can’t see. Understanding the production and role of these gases is critical not only for grasping chemical concepts but also for evaluating environmental impacts, such as greenhouse gas emissions from burning fossil fuels.