Reactants are the substances present at the start of a chemical reaction. In crossword form, the clue “chemical reaction ingredients” most directly points to reactants, because reactants are the starting materials that rearrange their atoms to form products.
Reaction vocabulary
A chemical reaction is represented by a chemical equation. The substances written on the left side of the reaction arrow are reactants, and the substances written on the right side are products. The arrow separates what is present before the reaction from what is formed after the reaction.
For the formation of water, hydrogen gas and oxygen gas are the reactants, while water is the product:
Meaning of “ingredients” in chemistry
The word “ingredients” is informal, but its chemistry meaning is precise. Reactants are not merely mixed materials; they are the substances whose atoms are rearranged during the reaction. Chemical bonds in the reactants are broken, new bonds form, and the products contain the same atoms arranged in a different way.
Balanced-equation context
The balanced equation for water formation contains coefficients that preserve the number of each type of atom:
On the reactant side, \(2\text{H}_2\) contains \(4\) hydrogen atoms, and \(\text{O}_2\) contains \(2\) oxygen atoms. On the product side, \(2\text{H}_2\text{O}\) also contains \(4\) hydrogen atoms and \(2\) oxygen atoms:
The equation demonstrates the law of conservation of mass. Reactants are not lost; their atoms are reorganized into products.
Reactants and products
| Term | Position in equation | Chemical meaning | Example in water formation |
|---|---|---|---|
| Reactants | Left of the arrow | Starting substances consumed or transformed during the reaction | \(\text{H}_2\) and \(\text{O}_2\) |
| Products | Right of the arrow | Substances formed by rearrangement of atoms | \(\text{H}_2\text{O}\) |
| Coefficient | Before a formula | Number of formula units, molecules, or moles represented | \(2\) in \(2\text{H}_2\text{O}\) |
| Reaction arrow | Between reactants and products | Direction of chemical change | \(\longrightarrow\) |
Common crossword confusion
The answer is reactants, not reagents in the usual introductory chemistry sense. A reagent is a substance used to cause, test for, or participate in a chemical process, often in a laboratory context. A reactant is the broader equation term for a starting substance that appears before the reaction arrow.
Final answer: the chemical reaction ingredients are reactants.