Chapter 11 Chemical Reactions

Hindenburg Ship Hydrogen gas combined with Oxygen which caused the ship to catch fire

Chemical reactions Take place after you eat

Photosynthesis

In a Chemical reaction One or more substances change into one or more new substances

Writing chemical equations Word Equations Reactants Products Iron + Oxygen Iron(III) Oxide Hydrogen Peroxide Dihydrogen monoxide + Oxygen Methane + oxygen Carbon dioxide + Dihydrogen monoxide

Chemical Equations Skeleton Equations - Equation that does not show the amounts of the reactants and the products Fe + O2 Fe2O3 Unbalanced equation !!!!!

One can add more information to the skeleton equations: To indicate if the reactants and products are liquids, solids or gases you use parentheses Fe(s) + O2(g) Fe2O3 (s) To indicate a catalyst (a substance that speeds up the reaction but is not used in the reaction) you place the catalyst over the arrow MnO2 H2O2 (aq) H2O (l) + O2 (g)

Used to separate two reactants or two products “yields” Symbol Explanation + Used to separate two reactants or two products “yields” Reaction is reversible (s) Solid state (l) Liquid state (g) Gaseous state (aq) Aqueous solution, dissolved in water Heat is applied to reaction Catalyst used in reaction heat catalyst

Balancing Equations Reactants Products Frame + wheel + hanlebar + pedal Bicycle F + 2 W + 1 H + 2 P FW2HP2

Balanced!! Calcium + Oxygen Calcium Oxide First write the skeleton equation Ca + O2 CaO Now balance Balanced!! 2 Ca + O2 2 CaO 2 1 Ca 2 1 Ca 2O 2 1 O

Balanced!! Hydrogen + oxygen Dihydrogen monoxide First write the skeleton equation H2 + O2 H2O Now balance 4 2 H 2 H 4 2 O 2 1 O Balanced!! 2 H2 + O2 2 H2O

Types of Chemical Reactions combination decomposition Single-replacement Double-replacement combustion

Combination Reactions (Synthesis) Chemical change in which two or more substances react to form a single new substance 2 Mg(s) + O2(g) 2 MgO(s) Metal + nonmetal 2 K(s) + Cl2(g) 2 KCl(s) SO2 (g) S (s) + O2(g) Two nonmetals two possibilities 2 S (s) + 3 O2(g) SO3 (g)

**Requires heat or electricity Decomposition Reactions Chemical change in which a single compound breaks down into two or more simpler products **Requires heat or electricity 2 HgO(s) heat 2 Hg(l) + O2(g) 2 H2O(l) electricity 2 H2(g) + O2(g)

Single-replacement Reactions Chemical change in which one element replaces a second element in a compound Zn(s) + H2SO4(aq) ZnSO4(aq) + H2(g) Cl2(g) + 2 NaBr(aq) 2NaCl(aq) + Br2(aq)

Double-replacement Reactions Chemical change involving an exchange of positive ions between two compounds 2 NaCN(aq) + H2SO4(aq) 2 HCN(aq) + Na2SO4(aq) NaOH(aq) + Fe(NO3)3 (aq) Fe(OH)3(s) + 3 NaNO3(aq) **Solution containing two ionic compounds

Combustion Reactions Chemical change in which an element or compound reacts with oxygen often producing energy in the form of heat or light CH4 (g) + 2 O2(g) CO2 (g) + 2 H2O(l) 2HCOOH (aq) + O2(g) 2CO2 (g) + 2 H2O(l) hydrocarbon + oxygen  carbon dioxide + water

** The number of elements and/or compounds reacting is a good indicator of possible reaction types and possible products- you can make predictions

Check what you know!! What are the five different types of reactions? What type of reaction are the following? C3H6 + O2 → CO2 + H2O Li + O2 → Li2O Zn + AgNO3 → Ag + Zn(NO3)2 Combination, decomposition, single-replacement, double-replacement, combustion Combustion Combination Single-replacement

Predict the type of reaction that will occur? An aqueous solution of two ionic compounds. Reactant is a single compound. The reactants are two elements. The reactants are oxygen and a compound of carbon and hydrogen. Double-replacement Decomposition Combination Combustion

Many important reactions take place in water Reactions in Aqueous Solution Net Ionic Equations Many important reactions take place in water Net ionic equations are different that the equations we are used to writing. We used to write equations like this: AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq)

Complete Ionic Equations Shows the dissolved ionic compound as separate ions Ag+(aq) + NO3-(aq) + Na+(aq) + Cl-(aq) AgCl(s) + Na+(aq) + NO3- (aq) Spectator ions - Ion that appears on both sides of the equation but is not involved in the reaction Net Ionic Equations Equation that shows only the particles that are directly involved in the reaction Ag+(aq) + Cl-(aq) AgCl(s)

Predicting the formation of a precipitate Compounds Solubility Salts of alkali metals and ammonia Soluble Nitrate salts and chlorate salts Sulfate salts, except compounds with Pb, Ag, Hg, Ba, Sr, Ca Chloride salts except compounds with Ag, Pb, Hg Carbonates, phosphates, chromates, sulfides and hydroxides Insoluble

First write the complete ionic equation Check what you know!!! Write a balanced net ionic equation. Pb(NO3)2(aq) + H2SO4(aq) → PbSO4(s) + HNO3(aq) First write the complete ionic equation Pb2+(aq) + NO3- (aq) + H+(g) + SO42-(aq) PbSO4(s) + H+(g) + NO3- (aq) Then find the spectator ions and cross them out Finally, write the net ionic equations Pb2+(aq) + SO42-(aq) PbSO4(s)