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Chemical Reactions Chapter 11

Today’s Objectives Be able to indicate when a chemical change has occurred. Understand the Law of Conservation of Mass

What is a chemical reaction? A change in which one or more reactants change into one or more products Characterized by the breaking of bonds in reactants and the formation of bonds in products A change that produces matter with a different composition than the original matter Taking one thing and making it something completely different!

Indicators of a Chemical Change Change in color Heat absorbed or released Formation of a gas Formation of a precipitate Odor given off

Balancing Equations Chemical Equation: an expression that represents a chemical reaction. Law of Conservation of Mass: No atoms are created or destroyed in chemical reactions. Atoms are just rearranged. Reactants  Products #atoms of each element in the reactants = # atoms of each element in the products

Chemical Reactions

4 Types of Chemical Reactions Synthesis Decomposition Single Replacement Double Replacement

Synthesis Two or more reactants combine to form a single product. 4Fe (s) + 3O2 (g)  2Fe2O3 (s) A + B  AB

Decomposition A single reactant forms two or more products. NH4NO3 (s)  N2O (g) + 2H2O (g) AB  A + B

Single-Replacement (Single Displacement) One element takes the place of another element in a compound. (“cutting in”) Cationic: Fe (s) + CuSO4 (aq)  FeSO4 (aq) + Cu (s) A + BC  AC + B Anionic: Cl2 (g) + 2NaBr (aq)  2NaCl (aq) + Br2 (l) A + BC  BA + C

Double-Replacement (Double Displacement) The positive ions of two ionic compounds switch places. (“switching partners”) At least one of the products is a precipitate, water, or a gas. Pb(NO3)2 (aq) + 2 KI (aq)  PbI2 (s) + 2 KNO3 (aq) AB + CD  AD + CB

Acid-Base (Double Replacement) An acid and base react to form water and a salt. HCl(aq) + NaOH(aq)  H2O(l) + NaCl (s) AB + CD  AD + CB acid + base  water + salt

Combustion Reaction 2 C2H2 (g) + 5 O2 (g)  4 CO2 (g) + 2 H2O (g) + energy What makes our engines run. Any time you burn an organic substance, you are creating a combustion reaction. Often a hydrocarbon fuel burning in oxygen to produce CO2 & H2O.

Predicting Products Use Reference Table to predict type of reaction. Guidelines for Predicting the Products of Selected Types of Chemical Reaction Key: M = Metal NM = Nonmetal Predicting Products

Practice Match each reaction to the best fitting reaction type. 1. ____ C3H8 + O2 -> H2O + CO2 2. ____ Mg + O2 -> MgO 3. ____ Ca + HCl -> CaCl2 + H2 4. ___ KClO3 -> KCl + O2 5. ___ HCl + NaOH -> NaCl + H2O 6. ___ NaNO3 + Ag -> AgNO3 + Na 7. ___ CH4 + O2 -> CO2 + H2O Reactions A. Synthesis B. Decomposition C. Combustion D.Single Displacement E. Double Displacement

Chemical Reactions Chapter 11

Warm Up for Tuesday, October 28 Match each reaction to the best fitting reaction type. 1. ____ C3H8 + O2 -> H2O + CO2 2. ____ Mg + O2 -> MgO 3. ____ Ca + HCl -> CaCl2 + H2 4. ___ CH4 + O2 -> CO2 + H2O 5. ___ Na + O2 -> Na2O 6. ___ H2SO4 + MgO -> H2O + MgSO4 7.___ H2O2 -> H2O + O2 Reactions A. Synthesis B. Decomposition C. Combustion D.Single Displacement E. Double Displacement

Writing Chemical Reactions Chemical Equation: an expression that represents a chemical reaction. A balanced chemical equation tells: What elements and/or compounds are involved The relative amounts of each substance involved Chemical equations MUST: Include the correct formula for the species involved Satisfy the Law of Conservation of atoms Tell the relative number of moles (quantity) of each species

Symbols you might see: Physical States: (g) – gas (l) – liquid (s) – solid or precipitate (aq) – substances dissolved in water  - reversible arrow reaction can go forward or backwards Δ – heat involved in the reaction MnO2 – catalyst Substance that speeds up the reaction but is not used up in the reaction

How to write a balanced chemical equation: 1. Decide which species are reactants & which are products 2. Write each species as a correct chemical formula. 3. Write the formulas for the reactants on the left side of the paper. 4. Place an arrow () after the reactants to indicate what is produced. 5. Write formulas for the products on the right side of the arrow. 6. Balance the chemical equation by adjusting the coefficients in front of the species to satisfy the Law of Conservation of Atoms. Same number of atoms of each element on both sides of the arrow Reactants Products Yields

Law of Conservation of Atoms During any chemical reaction, the mass of the products is always equal to the mass of the reactants. Matter cannot be created or destroyed. In any chemical reaction, mass is conserved. We use coefficients to balance chemical equations so that it obeys the Law of Conservation of Atoms!

Rules for Balancing an Equation: 1. Write out the numbers of each element for each side. 2. Add coefficients to balance elements ONE AT A TIME. Keep a running tally of the numbers of each element. Check each number after each coefficient added. Balance complicated compounds FIRST. Balance elements that appear alone or as diatomic molecules LAST. Save Oxygen & Hydrogen for LAST. 3. Reduce coefficients to simplest ratio, if necessary.

Example: Ammonium chloride reacts with calcium hydroxide to produce calcium chloride, ammonia, and water. 2 NH4Cl + Ca(OH)2 CaCl2 + 2 NH3 + 2 H2O N : H : Cl : Ca : O : 1 2 N : H : Cl : Ca : O : 1 2 6 10 5 8 10 1 2 2 1 1 2 1 2

Practice: Write the chemical equation & balance: Sodium hydrogen carbonate decomposes into sodium carbonate, carbon dioxide, and water. NaHCO3  Na2CO3 + CO2 + H2O 2 Na 1 H 1 C 1 O 3 ---- 2 ---- 6 Na 2 H 2 C 2 O 6

Practice 1) ____ NaCl + ____ F2  ____ NaF + ____ Cl2   2) ____ H2 + ____ O2  ____ H2O 3) ____ Pb(OH)2 + ____ HCl  ____ H2O + ____ PbCl2

Today’s Objective Predict Products for Reactions using Reference Table Understand the rules governing Single-Replacement Reactions Complete the Reactivity of Metals Lab

Predicting Products using Reference Table If you are two different elements as reactants SYNTHESIS If you have only one reactant DECOMPOSITION If you have an element (exculding O2) & a compound SINGLE-REPLACEMENT If you have two aqueous compounds DOUBLE-REPLACMENT If you have a hydrocarbon & O2 COMBUSTION

Use Reference Table to Decide which rule to use! Example: Mg + O2 -> Mg + N2 -> Mg+ O2 Mg3N2 Practice Predicting Products: Ca + Cl2 -> ZnCl2 -> Li2O -> K + S ->

Single Replacement Reactions Use Activity Series to Determine if a Reaction Will Occur. A lone element will replace an element in a compound if it is MORE REACTIVE (higher on chart). The element that is by itself MUST be higher on the chart than the one in the compound!

Decide if the reaction will occur: Fe (s) + Pb(NO3)2 (aq)  Ni (s) + MgCl2 (aq)  Cl2 (aq) + NaI (aq)  Ca (s) + CuBr2 (aq)  K (s) + Al(NO3)3 (aq)  I2 (s) + MnBr2 (aq)  Mg (s) + AgNO3 (aq)  Cl2 (s) + SrF2 (aq)  YES NO

Predict the Products Ca (s) + CuBr2 (aq)  K (s) + Al(NO3)3 (aq)  I2 (s) + MnBr2 (aq)  Mg (s) + AgNO3 (aq)  Cl2 (s) + SrF2 (aq) 

Double Replacement Reactions Reminder: At least one product is a precipitate, water, or a gas. Use solubility rules to determine which product is the precipitate. Precipitate = solid (insoluble) Both reactants are AQUEOUS. Only ONE product can be AQUEOUS. The other must be SOLID, LIQUID, or GAS.

Solubility Rules Must know the NAME of the compound before determining its solubility!

Predicting Products Single Replacement Double Replacement Use ACTIVITY SERIES The element that is by itself MUST be higher on the chart than the element in the compound for the reaction to occur Metal replace Metals Nonmetals replace Nonmetals Double Replacement Use SOLUBILITY RULES One product MUST be INSOLUBLE Do NOT check solubility of reactants!

PbNO3(aq) + AgI(s) RbI (aq) + AgNO3 (aq)  Na3PO4 (aq) + MnCl2 (aq)  Li2CO3 (aq) + MoBr6 (aq)  Ca(NO3)2 (aq) + Al(OH)3 (aq)  CuCl2 (aq) + Na2CO3 (aq)  BaCl2 (aq) + K2SO4 (aq)  NaCl(aq) + Mn3(PO4)2(s) LiBr(aq) + Mo(CO3)3(s) Ca(OH)2(s) + Al(NO3)3(aq) NaCl(aq) + CuCO3 (s) KCl(aq) + BaSO4 (s)

Reactions in Aqueous Solution Ionic compounds dissociate into ions in water! Overall equation: AgNO3(aq) + NaCl(aq) AgCl(s)+ NaNO3(aq) Ionic Equation: Ag+(aq) +NO3- (aq) +Na+ (aq) +Cl- (aq) AgCl (s) +Na+ (aq) +NO3 (aq) Shows dissolved ionic compounds as dissociated free ions Only separate AQUEOUS compounds into ions!

Ag+(aq) +NO3- (aq) +Na+ (aq) +Cl- (aq) AgCl (s) +Na+ (aq) +NO3 (aq) Net Ionic Equations Ag+(aq) +NO3- (aq) +Na+ (aq) +Cl- (aq) AgCl (s) +Na+ (aq) +NO3 (aq) Spectator ions: Ions that do not participate in the reaction: Na+, NO3- Net ionic equation: Shows only ions that are active in the reaction: Ag+ (aq) + Cl- (aq)  AgCl (s) Balancing Net Ionic Equations: must be balanced with respect to both mass (atoms) and charge.

Practice: Write the balanced net ionic equation. Pb (s) + AgNO3 (aq)  Ag (s) + Pb(NO3)2 (aq) FeCl3 (aq) + KOH (aq)  Fe(OH)3 (s) + KCl (aq)