Transcript Chapter 9
Chemical Equations Ch.9 (9-1) Chemical Rxn • Substances changed into something different • Reactants Products – Same type & # of atoms on each side, just rearranged differently Evidence of Chemical Change 1. 2. 3. 4. Heat, light, or sound Gas Precipitate (ppt) Color change Physical Change • Same composition before & after rxn • Ex: melting, boiling H2O(s) H2O(l) Energy • Chemical rxns absorb or release E • Exothermic: release E – Reactants Products + E • Endothermic: absorb E – Reactants + E Products Activation E • Particles must collide for a chemical rxn to occur & enough E must be present • Spontaneous rxn: occurs naturally w/out extra E • Nonspontaneous: needs more E to start (9-2) Chemical Equations • Describes type & # of atoms that are rearranged during a rxn • Word eq.: – Ethanol + oxygen carbon dioxide + water • Formula eq.: – C2H5OH + O2 CO2 + H2O Coefficients 2 K + Cl2 2 KCl • 2 K tells how many atoms react • The 2 applies to everything that follows it – 2 KCl = 2 K & 2 Cl • If the coef. is followed by a subscript they are multiplied – 2 H 2O = 4 H & 2 O Subscripts & Superscripts 2 K + Cl2 2 KCl • Cl2 refers to 2 atoms of Cl – Diatomics: BrINClHOF CaCl2 Ca2+ + 2 Cl• Ca2+ tells the charge of an ion Tips for Balancing Rxns 1. Save H & O for last 2. Treat polyatomic ions as a single element if on both sides of rxn • • H2SO4 + Al Al2(SO4)3 + H2 1 sulfate 3 sulfates 3. Balance left to right Tips for Balancing Rxns 4. Balancing 1 element may unbalance others 5. If present, make sure charges balance on each side of eq. • HCl + H2O Cl- + H3O+ Net = 0 Net = 0 • Ag+ + Cu Cu2+ + Ag 2Ag+ + Cu Cu2+ + 2Ag Net = 2+ Net = 2+ (9-3) States Symbol (s) (l) (g) (aq) Meaning Solid Liquid Gas In aqueous soln (dissolved in water) • C6H12O6(aq) + 6O2(g) 6CO2(g) + 6H2O(l) + E Conditions • Conditions: – Yield: – Equilibrium: – Heat: heat .. – Temp./Pressure: – Catalyst: Pd 0ºC 1 atm Equation Info • Balanced eq. show proportions • C6H12O6 + 6O2 6CO2 + 6H2O 1 mol 6 mol 6 mol 6 mol Mole Ratio • Conversion factor used to convert from 1 type of mole to another • Compare coef. C6H12O6 + 6O2 6CO2 + 6H2O 1 mol C6H12O6 : 6 mol CO2 3 mol C6H12O6 x Mole Ratio 6 mol CO2 = 18 mol CO2 1 mol C6H12O6 Mole Ratio Practice Determine the # of moles of each product would be formed given 16.0 mol KClO3 2 KClO3 2 KCl + 3O2 + 78 kJ 1. List the known 16.0 mol KClO3 Mole Ratio Practice 2. Multiply by the mole ratio (moles that need to cancel on the bottom) 16.0 mol KClO3 x 2 mol KCl = 16 mol KCl 2 mol KClO3 16.0 mol KClO3 x 3 mol O2 = 24 mol O2 2 mol KClO3 Mole Ratio Practice 3. Now calculate how much E was given off in kJ 16.0 mol KClO3 x 78 kJ = 624 kJ 2 mol KClO3 Enthalpy • ∆H: total E of a system (absorbed or released) • Measured in Joules (J) • Exo: - ∆H – Stonger bonds produced • Endo: + ∆H – E added to break bonds Exo: Endo: (9-4) Types of Reactions 1. 2. 3. 4. 5. 6. Combustion Oxidation Synthesis Decomposition Displacement (Single Replacement) Double Displacement (Double Replacement) Combustion • Violently exo. rxn, usually w/ O2 • Produces CO2 & H2O • CH4 + 2O2 CO2 + 2H2O + 803 kJ Oxidation • Not as dramatic as combustion, but still involves O2 • Ex: rusting of iron 4Fe + 3O2 2Fe2O3 Synthesis • Atoms or molecules combine to form a more complex cmpd • A + B AB • 8 Fe + S8 8 FeS Polymerization • Series of synthesis rxns to make a very large molecule (polymer) High Density Polyethylene Decomposition • Single cmpd is broken down to produce 2 or more simpler substances • AB A + B • 2 H2O 2 H2 + O2 Displacement • Element replaces another element in a cmpd • AB + C A + BC • 2Al + 3CuCl2 2AlCl3 + 3Cu Activity Series • Order of elements tendency to react w/ H2O & acids • Displace those below it (less active), but not above (more active) • Farther away = quicker rxns • 2K + MgO K2O + Mg more active less active Displacement Practice • Mg + CuO MgO + Cu – More reactive Mg displaces the less reactive Cu • Sn + CaO SnO + Ca – No rxn! – Sn is less reactive than Ca Double Displacement • Ions from 2 cmpds interact in soln to form a product • AB + CD AD + CB • 2KI + Pb(NO3)2 PbI2 + 2KNO3 Rxn Classification Practice 1. NaOH + KNO3 NaNO3 + KOH – Double displacement 2. 2 C4H10 + O2 8 CO2 + 10 H2O – Combustion 3. 2 Fe + 6 NaBr 2 FeBr3 + 6 Na – Single displacement Rxn Classification Practice 4. CaSO4 + Mg(OH)2 Ca(OH)2 + MgSO4 – Double displacement 5. Pb + O2 PbO2 – Synthesis 6. Na2CO3 Na2O + CO2 – Decomposition Solubility Rules • Explain which substances dissolve & which form precipitates (ppt.) – Table 13-2, p.492 • Soluble = dissolves (aq) • Insoluble = ppt (s) Solubility Practice NO3- All nitrates are soluble. Cl- All chlorides are soluble except AgCl, Hg2Cl2, and PbCl2. • NaNO3 = aq • KNO3 = aq • AgCl = s • ZnCl2 = aq Ionic Equation • 2KI(aq) + Pb(NO3)2(aq) PbI2(s) + 2KNO3(aq) • Total Ionic Eq.: 2K+(aq) + 2I-(aq) + Pb2+(aq) + 2NO3-(aq) PbI2(s) + 2K+(aq) + 2NO3-(aq) • Spectator ion: ion that remains unchanged – K+, NO3- Net Ionic Equation • Includes only those cmpds that are involved in a chemical change – Omit spectators • 2I-(aq) + Pb2+(aq) PbI2(s)