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Introduction to Reactions. Chemical Equation. Reactants Products Fe + O 2 Fe 2 O 3 A catalyst is a substance that speeds up the reaction but is not changed by it. It is neither a reactant or a product. Signs of a Reaction. Release of a gas
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Chemical Equation • Reactants Products • Fe + O2 Fe2O3 • A catalyst is a substance that speeds up the reaction but is not changed by it. • It is neither a reactant or a product.
Signs of a Reaction • Release of a gas • CO2 is released when acid is placed in a solution containing CO32- ions • Formation of a solid (precipitate) • A solution containing Ag+ ions mixed with a solution containing Cl- ions • Heat is produced or absorbed • Acid and base are mixed together • Color changes
Common Symbols Symbol Meaning forms, produces ↔ reversible reaction (s) Solid state (l) Liquid state; water only (g) Gaseous state (aq) aqueous state, all liquids besides water heat/energy is supplied to the reaction Catalyst is used, here platinum
Features of a Chemical Equation Products and reactants must be specified using chemical symbols Reactants – written on the left of arrow Products – written on the right – energy is needed Physical states are shown in parentheses
Writing Equations • 2H2 (g) + O2(g) 2H2O(g) Identify the substance involved • Coefficients - how many? • Chemical Formula – of what? • Physical State – in what state? • Remember Diatomic Elements • Magic Seven
Example • Two atoms of aluminum react with three units of aqueous copper (II) chloride to produce three atoms of copper and two units of aqueous aluminum chloride? • How many? • Of what? • What physical state?
Example • Two atoms of aluminum react with three units of aqueous copper (II) chloride to produce three atoms of copper and two units of aqueous aluminum chloride? • How many? • Of what? • What physical state? 2 Al(s) + 3 CuCl2(aq) 3 Cu(s) + 2AlCl3(aq)
Describing Equations • Describing Coefficients: • individual atom = “atom” • covalent substance = “molecule” • ionic substance = “unit” 3CO2 2Mg 4MgO
Describing Equations • Describing Coefficients: • individual atom = “atom” • covalent substance = “molecule” • ionic substance = “unit” 3CO2 2Mg 4MgO 3 molecules of carbon dioxide 2 atoms of magnesium 4 units of magnesium oxide
Describing Equations Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g) • How many? • Of what? • In what state?
Describing Equations Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g) One atom of solid zinc reacts with two units of aqueous hydrochloric acid to produce one unit of aqueous zinc chloride and one molecule of hydrogen gas • How many? • Of what? • In what state?
Balancing Reactions • Law of conservation of mass - matter cannot be created or destroyed • mass of the products = mass of the reactants • Coefficient: # of moles of products & reactants • 4Fe + 3O2 2Fe2O3 • Diatomic elements (The Magic 7) H2, N2, O2, F2, Cl2, Br2, I2
Balancing Coefficient- how many of that substance are in the reaction • The equation must be balanced • All the atoms of every reactant must also appear in the products • Number of Hg on left? 2 • on right 2 • Number of O on left? 2 • on right 2
Examine the Equation H2 + O2 H2O • Is the law of conservation of mass obeyed as written? • NO • You never change subscripts • WRONG: H2 + O2 H2O2
Steps in Equation Balancing H2 + O2 H2O The steps to balancing: Step 1. Count the number of moles of atoms of each element on both product and reactant sides ReactantsProducts 2 mol H 2 mol H 2 mol O 1 mol O
Step 2. Determine which elements are not balanced – Oxygen is not balanced Step 3. Balance one element at a time by changing the coefficients H2 + O2 2H2O • This balances oxygen, but is hydrogen still balanced? 2H2 + O2 2H2O Step 4. Make sure the law of conservation of mass is obeyed ReactantsProducts 4 mol H 4 mol H 2 mol O 2 mol O
Practice Equation Balancing Balance the following equations: 1. C2H2 + O2 CO2 + H2O 2. AgNO3 + FeCl3 Fe(NO3)3 + AgCl 3. C2H6 + O2 CO2 + H2O 4. N2 + H2 NH3
Practice Equation Balancing Balance the following equations: 1. 2C2H2 + 5O2 4CO2 + 2H2O 2. 3AgNO3 + FeCl3 Fe(NO3)3 + 3AgCl 3. 2C2H6 + 5O2 4CO2 + 6H2O 4. N2 + 3H2 2NH3
Combination Reactions • Synthesis reactions • The joining of two or more elements or compounds, producing a product of different composition Examples: • metal + nonmetal salt: 2Na(s) + Cl2(g) 2NaCl(s) • H + Cl HCl • MgO(s) + CO2(g) MgCO3(s) A + B AB
Decomposition Reactions • Produce two or more products from a single reactant • Reverse of a combination reaction Examples: • 2HgO(s) 2Hg(l) + O2(g) • CaCO3(s) CaO(s) + CO2(g) • Removal of water from a hydrated material AB A + B
Replacement Reactions Single-replacement • One atom replaces another in the compound producing a new compound Examples: • Cu(s)+2AgNO3(aq) 2Ag(s)+Cu(NO3)2(aq) • 2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g) A + BC B + AC
Single Replacement Rxn. • Activity Series – lists metals in order of decreasing reactivity (p.333) • Reactive metals will replace any metal listed below it in the activity series • If the metal is below, no reaction occurs • Halogen(7A) can replace other halogens that are below it in the periodic table
Single Replacement Rxn. • 2K(s) + 2H2O(l) • Zn(s) + Cu(NO3)2(aq) • Cu(s) + Al2O3(aq) • Br2(aq) + 2NaI(aq) • Br2(aq) + NaCl
Single Replacement Rxn. • 2K(s) + 2H2O(l) 2KOH(aq) + H2(g) • Zn(s) + Cu(NO3)2(aq) Cu(s) + Zn(NO3)2(aq) • Cu(s) + Al2O3(aq) No reaction • Br2(aq) + 2NaI(aq) 2NaBr(aq) + I2(aq) • Br2(aq) + NaCl No reaction
Double Replacement • Two compounds undergo a “change of partners” • Two compounds react by exchanging atoms to produce two new compounds AB + CD AD + CB
Double Replacement Rxn. • Double-displacement reaction • Exchange of positive ions • Occur in aqueous solution To occur: • One of the products is slightly soluble and a precipitates forms • One product is a gas • One of the products is a molecular compound, like water
Types of Double-Replacement • Acid + base water and salt HCl(aq)+NaOH(aq) NaCl(aq)+H2O(l) • Formation of solid lead chloride from lead nitrate and sodium chloride Pb(NO3)2(aq) + 2NaCl(aq) PbCl2(s) + 2NaNO3(aq) AB + CD AD + CB
Precipitation Reactions • Chemical change in a solution that results in one or more insoluble products Solubility Rules (p.344) 1. salts of alkali metals and ammonia soluble 2. nitrate salts and chlorate salts soluble 3. sulfate salts, except compounds with Pb, Ag, Hg, Ba, Sr, and Ca soluble 4. Chloride salts, except with Ag, Pb, and Hg soluble 5. carbonates, phosphates, chromates, sulfides, and hydroxides most are insoluble
Predicting Whether Precipitation Will Occur • Recombine the ionic compounds to have them exchange partners • Examine the new compounds formed and determine if any are insoluble • Any insoluble salt will be the precipitate • Pb(NO3)2(aq) + NaCl(aq) (s) PbCl2 (?) + NaNO3 ( ?) (aq)
Precipitates Predict Whether These Reactions Form Precipitates • Potassium chloride and silver nitrate • Potassium acetate and silver nitrate
Precipitates Predict Whether These Reactions Form Precipitates • Potassium chloride and silver nitrate • KCl(aq) + AgNO3(aq) KNO3(aq) + AgCl(s) • Potassium acetate and silver nitrate • KC2H3O2+ AgNO3(aq) KNO3(aq) + AgC2H3O2(s)
Reactions with Oxygen • Reactions with oxygen generally release energy in the form of light or heat Combustion • Reactants: Oxygen and a hydrocarbons • Products: CO2 and H2O • Combustion of natural gas • CH4+2O2CO2+2H2O • Rusting or corrosion of iron • 4Fe + 3O2 2Fe2O3