How to calculate limiting reactant
In chemical reactions, reactants are often present in unequal amounts. The limiting reactant is the substance that will be completely consumed during the reaction, ultimately determining the maximum amount of product that can be formed. Properly identifying and calculating the limiting reactant is essential in both lab experiments and a variety of industrial applications. In this article, we discuss the steps to help you find and calculate the limiting reactant in a chemical reaction.
Step 1: Identify the Balanced Chemical Equation
First, you need to write down the balanced chemical equation for the reaction. This equation shows the stoichiometric relation between all reactants and products involved in the reaction. Balancing a chemical equation requires adjusting coefficients to ensure that there are equal numbers of each element on both sides of the equation.
Step 2: Determine Moles of each Reactant
To determine which reactant is limiting, it’s essential to convert each reactant’s mass into moles using their
respective molar masses found on a periodic table. Moles are calculated using this formula:
Moles = mass / molar mass
Moles describe a substance’s quantity in terms of its particles (atoms or molecules).
Step 3: Find Mole Ratios
Based on the stoichiometry of your balanced chemical equation, calculate and compare mole ratios for each reactant. Mole ratios can be determined by dividing the number of moles of one reactant by the number of moles required for a complete reaction according to stoichiometry.
Mole Ratio = moles of reactant / stoichiometric ratio
In most cases, you will need one mole ratio for reactant A versus B and another one for A versus C.
Step 4: Identify Limiting Reactant
The limiting reactant has the lowest value among all mole ratios calculated in step 3. This indicates that this reactant will be consumed first, making it the limiting factor controlling the amount of product formed. Take note that there are cases wherein all reactants are present in a stoichiometric balance and none would be a limiting factor.
Step 5: Calculate Expected Product Amounts
Finally, using the moles of the limiting reactant, you can calculate the expected amount of products formed in the reaction. Apply stoichiometry to relate moles of limiting reactant to moles of product and convert back to mass if necessary by multiplying with product’s molar mass.
Calculating limiting reactant is a vital skill for students in chemistry courses and crucial for professionals in industrial applications. Following these steps, properly balanced chemical equations, and accurate calculations ensure you’re accurately identifying the limiting reactant and predicting the maximum quantity of products that can be formed during a reaction.