# Reacting Quantities

## Definition

• Reacting quantities refer to the amounts of substances involved in a chemical reaction.
• This concept uses the ratio of moles of each substance, which can be determined from a chemical equation.
• It’s based on the principle that matter can neither be created nor destroyed (Law of Conservation of Mass).

## Key Points

• A balanced chemical equation provides the number of moles of reactants and products in a chemical reaction.
• The stoichiometric coefficients in the balanced equation give the molar ratio of the reactants to the products.
• For instance, in the equation 2H2 + O2 → 2H2O, 2 moles of hydrogen react with 1 mole of oxygen to produce 2 moles of water.
• The molar mass of a substance (measured in grams per mole) can be used to calculate the mass of a reactant or product if the number of moles is known, and vice versa.

## Calculation of Reacting Quantities

• The formula n = m/M can be used, where:
• n = number of moles
• m = mass of substance (grams)
• M = molar mass of substance (grams per mole).
• To find the mass of a substance required or produced, rearrange the equation to m = n*M.

## Understanding Limiting Reactants

• The limiting reactant is the substance that is completely used up in a chemical reaction.
• Determination of the limiting reactant is crucial as it determines the maximum amount of product that can be formed.
• Excess reactant(s) remain after the reaction has gone to completion.

## Importance

• Understanding reacting quantities is central to carrying out chemical calculations, planning industrial chemical processes, and conducting laboratory reactions.
• It is used in areas of scientific research and industry to predict the yield of a reaction to make it as effective and cost-efficient as possible.
• This understanding can also help avoid the production of unwanted or hazardous by-products.