A chemical reaction is a fundamental process where substances transform into new and different substances. This transformation involves a change in the chemical identity of the starting materials. Unlike physical changes, which alter a substance’s appearance but not its chemical makeup, chemical reactions result in entirely new substances with distinct properties.
From Reactants to Products
Chemical reactions begin with substances called reactants, which are the starting materials. These reactants undergo changes to form new substances known as products. For example, in the burning of methane gas, methane and oxygen are the reactants, while carbon dioxide and water are the products.
During a chemical reaction, the atoms within the reactants rearrange themselves. Existing chemical bonds between atoms in the reactants break, and new bonds form to create the products. This atomic rearrangement leads to the formation of substances with different chemical compositions and properties from the original materials. The process is not about creating or destroying atoms, but rather about reorganizing them into new molecular structures. This transformation is often represented by a chemical equation, where reactants are on the left side and products are on the right, separated by an arrow indicating the direction of the reaction.
The Rule of Conservation
A foundational concept in chemistry is the law of conservation of mass, which states that matter is neither created nor destroyed during a chemical reaction. This means that the total mass of the reactants before a reaction must be equal to the total mass of the products after the reaction. Atoms are simply rearranged, ensuring the same number and type of atoms are present before and after the reaction.
For instance, if 10 grams of reactants combine, they will yield 10 grams of products. This conservation of mass is why chemical equations must be balanced, ensuring that the number of atoms for each element is identical on both sides of the equation.
Products in Our Daily Lives
Chemical reactions and their products are evident in many everyday occurrences. Burning wood, for example, is a common chemical reaction where wood (composed of cellulose, hemicellulose, and lignin) reacts with oxygen. The products include carbon dioxide, water vapor, and ash, along with the release of heat and light.
Baking also involves numerous chemical reactions that transform raw ingredients into a finished product like a cake. When baking, ingredients like flour, eggs, sugar, and leavening agents such as baking soda or baking powder are the reactants. Baking soda reacts with acids in the batter to produce carbon dioxide gas, which creates bubbles and causes the dough to rise, resulting in a light and fluffy texture. The Maillard reaction, involving sugars and proteins, contributes to the browning of the crust and the development of complex flavors.
Another familiar example is the rusting of iron, which is an oxidation reaction. Iron reacts with oxygen in the presence of water to form hydrated iron(III) oxide, commonly known as rust. The reddish-brown, flaky substance of rust has properties entirely different from the original iron.