1.3: Stoichiometry of Chemical Reactions


This chapter will describe how to symbolize chemical reactions using chemical equations, how to classify some common chemical reactions by identifying patterns of reactivity, and how to determine the quantitative relations between the amounts of substances involved in chemical reactions—that is, the reaction stoichiometry.

• 1.3.0: Writing and Balancing Chemical Equations
Chemical equations are symbolic representations of chemical and physical changes. Formulas for the substances undergoing the change (reactants) and substances generated by the change (products) are separated by an arrow and preceded by integer coefficients indicating their relative numbers. Balanced equations are those whose coefficients result in equal numbers of atoms for each element in the reactants and products.
• 1.3.1: Formula Mass and the Mole Concept
The formula mass of a substance is the sum of the average atomic masses of each atom represented in the chemical formula and is expressed in atomic mass units. The formula mass of a covalent compound is also called the molecular mass. A convenient amount unit for expressing very large numbers of atoms or molecules is the mole. Experimental measurements have determined the number of entities composing 1 mole of substance to be $$6.022 \times 10^{23}$$, a quantity called Avogadro’s number.
• 1.3.2: Types of Reactions
Chemical reactions are classified according to similar patterns of behavior. This section will help you to differentiate between the different types of reactions which we commonly see in CHE 101 and to write balanced chemical equations for replacement reactions.
• 1.3.3: Reaction Stoichiometry
A balanced chemical equation may be used to describe a reaction’s stoichiometry (the relationships between amounts of reactants and products). Coefficients from the equation are used to derive stoichiometric factors that subsequently may be used for computations relating reactant and product masses, molar amounts, and other quantitative properties.
• 1.3.4: Reaction Yields
When reactions are carried out using less-than-stoichiometric quantities of reactants, the amount of product generated will be determined by the limiting reactant. The amount of product generated by a chemical reaction is its actual yield, which is often less than the amount of product predicted by the stoichiometry of the balanced chemical equation representing the reaction (theoretical yield). The extent to which a reaction generates the theoretical amount is expressed as its percent yield.
• 1.3.5: Exothermic and Endothermic Reactions
Differentiate between exothermic and endothermic reactions and graph the energy change in each.