Chapter 8 Chemical Reactions Chemistry by Addison - Wesley

8.1 Describing Chemical Change Word Equations In a chemical reaction, one or more substances change into one or more new substances Reactants Products Important to note that in a chemical reaction the atoms are neither created or destroyed; just rearranged

Chemical Equations Chemical equation is similar to a word equation only chemical symbols represent substances Skeleton equation represents the compounds without a quantity State of matter can also be added to a skeleton equation H2 (g) + O2 (g) H2O (l)

Balancing Equations Rules for Balancing Equations Determine the correct formulas for the reaction Write the formula with the reactants on the left and the products on the right Count the number of atoms of each element on each side Balance the elements one at a time using coefficients Check each atom to make sure that it is balanced Make sure the coefficients are in the lowest possible ratio

8.2 Types of Chemical Reactions Classifying reactions Five Categories Synthesis Decomposition Single-displacement Double-displacement Combustion

Synthesis Reactions In a synthesis reaction, two or more substances combine to form a single substance Two or more reactants One product H2 + O2 -> H2O

Decomposition Reactions In a decomposition reaction, one substance breaks down into two or more substances One Reactant Two or more products H2O -> H2 + O2 Often require heat or some sort of energy source to break down bonds in the compound

Single-Displacement Reactions In a single-displacement reaction, one element replace another in a compound Two reactants Two products Na + HCl -> H2 + NaCl Normally, the replacement occurs at the cation spot

Double-Displacement Reactions In a double-displacement reactions, two compounds exchange cations Two reactants Two products NaOH + HCl -> H(OH) + NaCl In most cases, one of the following will occur in a double-replacement reaction: 1) a precipitate forms, 2) a gas forms, or 3) a molecular compound forms

Combustion Reactions In combustion reactions, a compound reacts with oxygen often to produce heat or light One of the reactants will always be oxygen A hydrocarbon is often the other reactant Combustion of a hydrocarbon will produce H2O and CO2 C2H6 + O2 -> H2O + CO2 + heat

8.3 Reactions in Aqueous Solutions Net Ionic Equation In an aqueous solution, compounds ionize into solution Ions that are on both sides of the equation are called spectator ions These ions cancel out of the equation

Predicting the Formation of a Precipitate Solubility Rules for Ionic Compounds Salts of alkali metals and ammonia - soluble (exceptions some lithium compounds) Nitrate salts and chlorate salts - soluble (few exceptions) Sulfate salts - soluble (Compounds of Pb, Ag, Hg, Ba, Sr, and Ca are exceptions) Chloride salts - soluble (Ag and some Hg and Pb are exceptions) Carbonates, phosphates, chromates, sulfides, and hydroxides - insoluble (Alkali metals and ammonia)