A starting substance that is consumed and chemically transformed during a chemical reaction, appearing on the left side of a chemical equation before the reaction. Identifying reactants is the first step in understanding any reaction.
This concept is covered in depth in our complete chemistry definitions reference, with worked examples, practice problems, and common mistakes.
Definition
A starting substance that is consumed and chemically transformed during a chemical reaction, appearing on the left side of a chemical equation before the reaction.
💡 Intuition
What you start with — the ingredients that get used up to make something new.
🎯 Core Idea
Reactants appear on the left side of a chemical equation and are used up in the reaction.
Example
Notation
Reactants are written to the left of the reaction arrow (\to). The + sign separates multiple reactants. Coefficients before formulas indicate mole ratios.
🌟 Why It Matters
Identifying reactants is the first step in understanding any reaction. In industry, knowing which reactants to use and in what amounts determines manufacturing cost, safety, and efficiency of chemical production.
💭 Hint When Stuck
When identifying reactants in a problem, look at the left side of the arrow. First read the equation and list everything before the \to symbol. Then check that each substance is actually consumed (not a catalyst or solvent). Finally, note the coefficients — they tell you the mole ratios needed.
Formal View
Related Concepts
🚧 Common Stuck Point
Catalysts help reactions but aren't reactants—they're not consumed.
⚠️ Common Mistakes
- Including catalysts as reactants — catalysts speed up the reaction but are not consumed and do not appear in the net equation
- Confusing the solvent with a reactant — water in aqueous reactions is often just the medium, not a reactant
- Ignoring state symbols — (s), (l), (g), (aq) tell you important information about each reactant's physical form
Frequently Asked Questions
What is Reactant in Chemistry?
A starting substance that is consumed and chemically transformed during a chemical reaction, appearing on the left side of a chemical equation before the reaction.
When do you use Reactant?
When identifying reactants in a problem, look at the left side of the arrow. First read the equation and list everything before the \to symbol. Then check that each substance is actually consumed (not a catalyst or solvent). Finally, note the coefficients — they tell you the mole ratios needed.
What do students usually get wrong about Reactant?
Catalysts help reactions but aren't reactants—they're not consumed.
Prerequisites
Next Steps
How Reactant Connects to Other Ideas
To understand reactant, you should first be comfortable with chemical reaction. Once you have a solid grasp of reactant, you can move on to product and limiting reactant.
Want the Full Guide?
This concept is explained step by step in our complete guide:
Chemistry Terms and Definitions: Product, Reactant, Solution, Base, Molecule →Learn More
Visualization
StaticVisual representation of Reactant