# 2: Chemical Reactions

• 2.1: The Atomic Theory of Matter
This article explains the theories that Dalton used as a basis for his theory: (1) the Law of Conservation of Mass, (2) the Law of Constant Composition, (3) the Law of Multiple Proportions.
• 2.2: Masses of Atoms and Molecules
The atomic mass unit (u) is a unit that describes the masses of individual atoms and molecules. The atomic mass is the weighted average of the masses of all isotopes of an element. The molecular mass is the sum of the masses of the atoms in a molecule.
• 2.3: Stoichiometry
Quantities of substances can be related to each other using balanced chemical equations.
• 2.4: The Mole
The mole is a key unit in chemistry. The molar mass of a substance, in grams, is numerically equal to one atom's or molecule's mass in atomic mass units.
• 2.5: Mole-Mass and Mass-Mass Calculations
Mole quantities of one substance can be related to mass quantities using a balanced chemical equation. Mass quantities of one substance can be related to mass quantities using a balanced chemical equation. In all cases, quantities of a substance must be converted to moles before the balanced chemical equation can be used to convert to moles of another substance.
• 2.6: Chemical Equations
A chemical reaction is described by a chemical equation that gives the identities and quantities of the reactants and the products. In a chemical reaction, one or more substances are transformed to new substances. A chemical reaction is described by a chemical equation, an expression that gives the identities and quantities of the substances involved in a reaction. A chemical equation shows the starting compound(s)—the reactants—on the left and the final compound(s)—the products—on the right.
• 2.7: The Mole in Chemical Reactions
Balanced chemical reactions are balanced in terms of moles. A balanced chemical reaction gives equivalences in moles that allow stoichiometry calculations to be performed.
• 2.8: Activity: Balancing Chemical Equations
How do you know if a chemical equation is balanced? What can you change to balance an equation? Play a game to test your ideas!
• 2.9: Some Simple Patterns of Chemical Reactivity
By recognizing general patterns of chemical reactivity, you will be able to successfully predict the products formed by a given combination of reactants We can often predict a reaction if we have seen a similar reaction before.