# Knowing the mole ratio of a reactant and product relationship

### Limiting Reactant and Theoretical Yield - Chemistry LibreTexts

Calculate how much product will be produced from the limiting reagent. More often, however, reactants are present in mole ratios that are not . will see shortly that knowing the final mass of product can be useful. The balanced equation provides the relationship of 2 mol Mg to 1 mol O2 to 2 mol MgO. Understanding this is essential to solving stoichiometric problems. This is the mole ratio between two factors in a chemical reaction found through the . Molarity (moles/L) establishes a relationship between moles and liters. The relationship between the products and reactants in a balanced chemical equation Molar ratios, or conversion factors, identify the number of moles of each.

No, and this is normally the case with chemical reactions. There is often excess of one of the reactants. The limiting reagent, the one that runs out first, prevents the reaction from continuing and determines the maximum amount of product that can be formed. Example 3 What is the limiting reagent in this example? Aside from just looking at the problem, the problem can be solved using stoichiometric factors. Types of Reactions There are 6 basic types of reactions.

Combination is the addition of 2 or more simple reactants to form a complex product.

Determining the Mole Ratio

Decomposition is when complex reactants are broken down into simpler products. Single displacement is when an element from on reactant switches with an element of the other to form two new reactants. Double displacement is when two elements from on reactants switched with two elements of the other to form two new reactants. Acid- base reactions are when two reactants form salts and water. Molar Mass Before applying stoichiometric factors to chemical equations, you need to understand molar mass.

Molar mass is a useful chemical ratio between mass and moles. The atomic mass of each individual element as listed in the periodic table established this relationship for atoms or ions.

Since there is a ratio of 4: Variation in Stoichiometric Equations Almost every quantitative relationship can be converted into a ratio that can be useful in data analysis.

### Stoichiometric Calculations: Amounts of Reactants and Products - Chemistry LibreTexts

This ratio can be useful in determining the volume of a solution, given the mass or useful in finding the mass given the volume.

In the latter case, the inverse relationship would be used. A percent mass states how many grams of a mixture are of a certain element or molecule.

This is useful in determining mass of a desired substance in a molecule. If the total mass of the substance is 10 grams, what is the mass of carbon in the sample?

How many moles of carbon are there?

Given volume and molarity, it is possible to calculate mole or use moles and molarity to calculate volume. Hydrogen, therefore, is present in excess, and chlorine is the limiting reactant. Reaction of all the provided chlorine 2 mol will consume 2 mol of the 3 mol of hydrogen provided, leaving 1 mol of hydrogen nonreacted.

## 3.9 Stoichiometric Calculations: Amounts of Reactants and Products

An alternative approach to identifying the limiting reactant involves comparing the amount of product expected for the complete reaction of each reactant. The reactant yielding the lesser amount of product is the limiting reactant. Since enough hydrogen was provided to yield 6 moles of HCl, there will be non-reacted hydrogen remaining once this reaction is complete.

When H2 and Cl2 are combined in nonstoichiometric amounts, one of these reactants will limit the amount of HCl that can be produced. This illustration shows a reaction in which hydrogen is present in excess and chlorine is the limiting reactant.

A similar situation exists for many chemical reactions: The reactant you run out of is called the limiting reactant; the other reactant or reactants are considered to be in excess. One method is to find and compare the mole ratio of the reactants used in the reaction Approach 1. Another way is to calculate the grams of products produced from the given quantities of reactants; the reactant that produces the smallest amount of product is the limiting reagent Approach 2.

This section will focus more on the second method. Find the limiting reagent by looking at the number of moles of each reactant. Determine the balanced chemical equation for the chemical reaction.

Convert all given information into moles most likely, through the use of molar mass as a conversion factor. Calculate the mole ratio from the given information. Compare the calculated ratio to the actual ratio. Use the amount of limiting reactant to calculate the amount of product produced.

If necessary, calculate how much is left in excess of the non-limiting reactant. Find the limiting reagent by calculating and comparing the amount of product each reactant will produce.

Balance the chemical equation for the chemical reaction. Convert the given information into moles. Use stoichiometry for each individual reactant to find the mass of product produced. The reactant that produces a larger amount of product is the excess reactant.

To find the amount of remaining excess reactant, subtract the mass of excess reactant consumed from the total mass of excess reagent given. The key to recognizing which reactant is the limiting reagent is based on a mole-mass or mass-mass calculation: What we need to do is determine an amount of one product either moles or mass assuming all of each reactant reacts.

• 8.5: Limiting Reactant and Theoretical Yield
• Stoichiometry

Whichever reactant gives the least amount of that particular product is the limiting reagent. It does not matter which product we use, as long as we use the same one each time. It does not matter whether we determine the number of moles or grams of that product; however, we will see shortly that knowing the final mass of product can be useful.