Reactants are the inputs in a chemical reaction. A chemical reaction is a process of transformation where one set of substances changes into a different set of substances. These starting materials are chemically altered as their constituent atoms are rearranged. The process converts these initial inputs into new chemical outputs, which possess distinct chemical and physical properties.
Defining Reactants and Products
Reactants are the starting materials present before a chemical change begins. These substances are the inputs consumed during the reaction. For a reaction to occur, the chemical bonds within the reactant molecules must first be broken down.
The atoms from the broken bonds then rearrange and form new, stable chemical bonds. This rearrangement leads to the formation of products, which are the new substances generated by the reaction. Products always have different molecular structures and properties compared to the original reactants.
The Anatomy of a Chemical Equation
The relationship between the chemical inputs and outputs is formally represented by a chemical equation. In this standardized notation, the reactants are always written on the left side of the equation. This placement signifies their role as the starting ingredients for the process.
The products are always placed on the right side of the equation. An arrow separates the reactants from the products, and is read aloud as “yields” or “produces.” This arrow indicates the direction of the chemical transformation, showing the flow from input to output substances. A properly written equation also adheres to the law of conservation of mass, meaning the total number of atoms for each element is identical on both sides.
Basic Examples of Chemical Reactions
A common illustration of this input-output flow is the formation of water. In this reaction, hydrogen gas (\(\text{H}_2\)) and oxygen gas (\(\text{O}_2\)) serve as the reactants, or inputs. These two must combine for the process to occur.
The atoms from these reactant molecules rearrange to produce liquid water (\(\text{H}_2\text{O}\)), the product, or output. The balanced equation, \(2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}\), shows two distinct inputs yielding a single output. Another example is the combustion of methane (\(\text{CH}_4\)), where methane and oxygen (\(\text{O}_2\)) transform into the outputs of carbon dioxide (\(\text{CO}_2\)) and water (\(\text{H}_2\text{O}\)).