Final answer:
The number 2 before HCl in the equation H₂ + Cl₂ = 2HCl signifies the number of hydrogen chloride molecules formed and is used to balance the chemical equation. A coefficient indicates the amount of molecules or formula units represented in the reaction.
Step-by-step explanation:
In the chemical equation H₂ + Cl₂ = 2HCl, we write the number 2 before HCl to signify that two molecules of hydrogen chloride are formed in the reaction. This is necessary to balance the equation, ensuring that the number of atoms of each element is the same on both sides of the equation.
The number 2 in front of HCl indicates that for every molecule of hydrogen (H₂) and every molecule of chlorine (Cl₂) that react, two molecules of hydrogen chloride (HCl) are produced. Chemical equations use chemical formulas and coefficients to represent the reactants and products. A coefficient, such as the 2 in front of HCl, is a small whole number placed in front of a formula in an equation to indicate the number of molecules or formula units involved in the reaction.
The balanced equation H₂ + Cl₂ = 2HCl shows a reaction where one molecule of hydrogen gas reacts with one molecule of chlorine gas to produce two molecules of hydrogen chloride gas. It is crucial that chemical equations are balanced to follow the Law of Conservation of Mass, which states that matter cannot be created or destroyed in a chemical reaction.