Introduction:
Basically, the stoichiometry may be regarded as the branch of chemistry and chemical engineering which deals with the quantities of substances which enter into and are produced by chemical reactions. Stoichiometry gives the quantitative relationship between reactants and products in a chemical reaction. It can be utilized in microbial technology also.
Stoichiometry can be classified into two main categories:
1. Composition Stoichiometry:
Deals with mass relationships of elements in compounds
2. Reaction Stoichiometry:
Involves mass relationships between reactants and products in a chemical reaction
In ideal Stoichiometry – All reactants are converted into products.
Common Methods for solving all Stoichiometry Problems:
Mass-Mass Problems:
1. Start with a known mass of reactant or product and find an unknown mass of another reactant or product.
2. All other stoichiometry problems are derivations (shortened versions) of this larger solution:
Steps for solving problems:
1. Start with a correctly balanced chemical equation.
2. Use key words in the problem statement to identify substances as either reactants or products.
3. Determine what units you’ve been given and what you are being asked to find.
4. Label each step with the correct units the units from the numerator of the first step become the units in the denominator of the next step, and so forth.
5. Stop when you have an answer with the units that you are searching for.
Limiting Reactant:
The reactant that limits the amount of the other reactants that can combine and the amount of product that can be formed in a chemical reaction.
Excess Reactant:
It is the substance that is not used up completely in a reaction.
Identifying the Limiting Reactant:
1. Convert grams of each reactant to moles if the problem has not already been worked out.
2. Use molar ratios from the balance chemical equation to determine which reactant is limiting, and which reactant is in excess.
Stoichiometry with Limiting Reactants:
All calculations should start with the amount of the limiting reactant, not the excess reactant.
Calculating Percent Yield:
The ratio of the actual yield to the theoretical yield, multiplied by 100
