Stoichiometry deals with the calculation of the mass and volume of reactants and products in chemical reactions. The term stoichiometry was first introduced by the German chemist Jeremias Benjamin Richter (1762-1807) in the late 19th century. It relates to the relative amounts of reactants and products in a chemical reaction. His calculations are based on the fact that atoms cannot be created or destroyed. The number and types of atoms before and after the reaction are always the same.
There are several steps that must be taken when performing calculations using stoichiometry or a stoichiometric worksheet. First, write down the equivalent chemical equation. Second, substances whose mass/volume have been stated or determined in the calculation are marked or underlined.
Third, the atomic weight/mol/molar volume of the substance that is underlined is written depending on the problem or question. Then, the actual amount of the substance that has been underlined is written down. Finally, substances whose mass/volume must be calculated are marked with a question mark.
The calculations in the stoichiometric worksheet provide quantitative information and solve problems related to three categories, namely the mass-mass relationship (w / w), the mass-volume relationship (w / V), and the volume-volume relationship (V / V). In the mass-mass relationship, the mass of one of the reactants or products is known, while the mass of some of the other reactants or products must be calculated.
In the mass-volume relationship, the mass/volume of one reactant or product is given and the mass/volume of the other must be calculated. Meanwhile, in the volume-volume relationship, the volume of one of the reactants or products is given and the volume of the other must be calculated.
Use Limiting Reagents
In stoichiometry, Stoichiometric calculations also use limiting reagents. Limiting reagents are the reactants or reagents that are used up and limit the number of products formed (with the completion of the reaction) in a chemical reaction.
The empirical formula is the simplest integer ratio of the number of moles of each element in a compound. The molecular formula is the actual number of moles of each element in 1 mole of the compound. The molecular formula can be identical to the empirical formula or it is an integer multiple of the empirical formula. For example, phosphoric acid (H3PO4) has identical molecular and empirical formulas. Glucose has the molecular formula C6H12O6 which is a multiple of 6 times the empirical formula, CH2O.
molecular formula ≡ (empirical formula) n} molecular formula = n ×} empirical formula, n = 1, 2, 3,…
Basic Stoichiometric Solutions
The term “concentration” of solution expresses the amount of solute dissolved in a specified amount of solvent or a specified amount of solution. The concentration of a solution can be expressed in terms of molarity. Molarity (M) is defined as the number of moles of solute per liter of solution.
Basic Ideal Gas Stoichiometry
In stoichiometry, The molar volume, Vm, is defined as the volume of 1 mole of the entity (atom, ion, molecule, unit formula) of matter. The unit of molar volume (Vm) is L / mol.
Avogadro’s law states that at a certain and constant pressure and temperature, the volume of a gas is directly proportional to the amount of gas. In the STP state (P = 1 atm, T = 273 K), Vm of the ideal gas = 22.414 L / mol. In the RTP / ATP state (P = 1 atm, T = 298 K), Vm of the ideal gas = 24 L / mol
Under certain circumstances, the ideal gas law applies: where R is the gas constant, R = 0.08206 L ∙ atm/mol ∙ K = 8.314 J / mol ∙ K
Writing and Balancing Chemical Reaction Equations
A chemical reaction equation is a statement written with a molecular formula that provides information on the identity and quantity of substances involved in a chemical or physical change. All the substances that react, called reagents/reactants, are placed to the left of the arrow, where the arrow to the right points to the product, that is, all the substances that are produced from the reaction.
In a reaction equation, there is a reaction coefficient, which is the number to the left of the molecular formula for multiplying all the atoms in the molecular formula. The ratio of reaction coefficients can be interpreted as the mole ratio of the substances in the reaction. For each reactant and product, the substance (s (solid), l (liquid), g (gas), or aq (water-solvent solution)) is written in parentheses to the right of the respective molecular formula.