Lecture Notes on Stoichiometry, Mole Concept, and Balancing Equations

Flashcards on Stoichiometry

Stoichiometry

Deals with the mole concept, balancing equations, and stoichiometric coefficients in chemical reactions.

Balancing Equations Tip

Balance everything that's not oxygen and hydrogen first. Leave oxygen and hydrogen until the end.

Mole (mol)

A unit of measurement of amount. One mole contains 6.022 x 10^23 entities (Avogadro's number).

Chemical Reactions Ratio

Reactants react in a certain ratio, just like ingredients in a recipe. The stoichiometry dictates this ratio.

Combustion Reaction

A reaction of a hydrocarbon in oxygen, producing heat and typically carbon dioxide and water.

Stoichiometric Coefficient

The number in front of a chemical formula in a balanced equation, representing the number of moles of that species involved in the reaction.

Stoichiometric Ratio (Molar Ratio)

The ratio in which reactants combine and products are formed in a chemical reaction, based on the stoichiometric coefficients.

Butane

A hydrocarbon (C4H10) that combusts in the presence of oxygen to produce carbon dioxide and water.

The Law of Conservation of Mass

Mass cannot be created or destroyed, so the amount of each element must be the same on both sides of a balanced chemical equation.

Balancing Equations – Step 1

Write the unbalanced equation using molecular formulas for reactants and products.

Polyatomic Ions

Ions consisting of two or more covalently bonded atoms that appear unchanged on both sides of the chemical equation arrow should be balanced as a group.

Importance of Moles

Moles are used to describe amounts of a substance in chemistry. One mole of substance A does not weigh the same as one mole of substance B.

Empirical Formula

The simplest whole number ratio of elements in a compound.

Molecular Formula

Shows the actual number of atoms of each element in a molecule.

Percent Composition

Expresses the relative amount of each element in a compound as a percentage.

Formula for Percent Composition

Percentage of element = (mass of element in compound / mass of entire sample) x 100%

Empirical Formula Determination

Assume a 100g sample, convert percentages to masses, convert masses to moles, and find the simplest whole number mole ratio.

Molecular Formula Determination

Determine the empirical formula first and use the molecular formula mass in order to determine the multiplier to apply to generate the molecular formula.

Process Chemistry

Knowledge of limiting reagents, stoichiometry or percentage yields may be used during pharmaceutical or other industrial chemical production to streamline costs.

Solving Stoichiometry Problems

Balance the chemical equation; convert masses to moles; relate moles of given compound to moles of desired compound (product); calculate grams if needed.

Moles of Carbon

Number of moles of carbon = six / 12 = 0.5.

Limiting Reagent

The reagent that limits how much product can be made. Example: Carbon for core chemical reactant.

Balanced equation for Sodium Reaction

Two moles of sodium react with two moles of water to react to produce two moles of sodium hydroxide and one mole of hydrogen.

Determining the Limiting Reagent

To determine the limiting reagent the numbers must be compared so that they are per mole by dividing the number of moles of each by each molecule's stoichiometric coefficient.