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B-2 1/3-4: 8.1/8.2 Chem and phys change, Bal Eq WS 1,2 M 1/7: Rev Bal, 8.3 Types chem eq WS 3, 4 WS 5 and 6 are extra work on balancing and typing equations B-1 1/8-9: Quiz 8.1-8.3: Ratios, 9.1 3-Step process B-2 1/10-11: 3-Step, 9.2 Lim react, % Yield M 1/14: Quiz 3-Step, % Yield B-1 1/15-16: Lab B-2 1/17-18: Rev Lab M 1/21: Rev Chap B-1 1/22-23: Test CHEMICAL REACTIONS Reactants: Zn + I2 Product: Zn I2 Chemical Equations • Show a chemical reaction – Chem reactions describe a chemical change • Chem reactions = chemical change – Reactants converted into products – Formation of new substance – Particles must collide for a reaction to occur • Old bonds broken in reactants (endo) • New bonds formed in products (exo) – Atoms (and mass) are conserved – Energy changes can also be described Collision Theory • For reactant molecules to cause a chemical change they must collide • 2 criteria must be met for a collision to cause a chem reaction to occur – – – – – 1. proper energy to break old bonds 2. proper orientation to form new bonds Collision alignment.MOVCollision Effective.MOV Collision no energy.MOV Physical Change Changes in physical properties melting boiling dissolving No change occurs in the identity of the substance Changes in energy occur in physical changes Chemical Change • Atoms in the reactants are rearranged to form one or more different substances • Old bonds are broken; new bonds form Examples: Fe and O2 form rust (Fe2O3) Ag and S form tarnish (Ag2S) Learning Check Classify each of the following as a 1) physical change or 2) chemical change A. ____ a burning candle B. ____ melting ice C. ____ toasting a marshmallow D. ____ cutting a pizza E. ____ polishing silver Solution Classify each of the following as a 1) physical change or 2) chemical change A. __2__ a burning candle B. __1__ melting ice C. __2__ toasting a marshmallow D. __1__ cutting a pizza E. __2__ polishing silver Chemical Reaction A process in which at least one new substance is produced as a result of chemical change. Evidence of Chem Rx • • • • Formation of a gas Formation of a precipitate Color change Large energy change – Exothermic – feels warm • Heat, sound, light – Endothermic – feels cold • Photosynthesis • Know all examples from text pg 261 A Chemical Reaction Reactants Products Chemical Reactions – Chemical reactions occur when old bonds between atoms are broken and new bonds between atoms are formed – Chemical reactions involve chemical changes in matter. • New substances with new properties are created (products). – Chemical reactions can absorb or give of energy. – Symbols represent names of reactants and product • formulas describe compounds • chemical equations describe a chemical reaction Heat in Chemical Reactions Energy changes always accompany chemical and physical changes Heat is the primary form of energy exchanged during chemical reactions One reason why reactions occur is that the products attain a lower, more stable energy state than the reactants. Enthalpy • Enthalpy = H • total heat content in a substance • Sum of potential and kinetic energies • Can calc Ek = ½mv2 • Cannot calc Ep • Cannot determined H for any system • We can and do measure the change in energy during a reaction = DH Energy Changes in Chem Eq • DH = change in energy (enthalpy) – DH = energyprod – energyreactants – DH (+) = endothermic rx = +200 kJ – DH (-) = exothermic rx = -100 kJ Endo Chem Rx • Reactant + 200 kJ Product – Feels cold - energy absorbed – Energy must be added to keep rx going – Higher energy, less stable prod formed Exo Chem Rx • Reactant Product + 100 kJ – Feels warm - energy given off – Most spontaneous reactions are exo – Prod lower energy, more stable, than reactants Chemical Equations Their Job: Depict the kind of reactants and products and their relative amounts in a reaction. 4 Al (s) + 3 O2 (g) ---> 2 Al2O3 (s) The numbers in the front are called stoichiometric coefficients The letters (s), (g), (l) and (aq) are the physical states of compounds. Parts of a Chemical Equation – Chemical equations shows the conversion of reactants (the molecules shown on the left of the arrow) into products (the molecules shown on the right of the arrow). • A + sign separates molecules on the same side • The arrow is read as “yields” or “produces” • Example C + O2 CO2 • This reads “carbon plus oxygen react to yield carbon dioxide” Symbols Used in Equations • Solid (s) p 265 • Liquid (l) table 2 • Gas (g) • Aqueous solution (aq) • Formation of precipitate () or (s) • Escaping gas () or (g) H2SO4 • Catalyst • Heating D Special Conditions • • • • • • • produces or yields reversible reaction. Both reactants and products present at end of reaction D reactants are heated 10˚C rx carried out at specific temp 1 atm pressure rx is conducted under Pd catalyst used in the reaction State symbols table p. 265 Chemical Equations Because of the principle of the conservation of matter, an equation must be balanced. It must have the same number of atoms of the same kind on both sides. Lavoisier, 1788 Subscripts vs. Coefficients • The subscripts tell you how many atoms of a particular element are in a compound. The coefficient tells you about the quantity, or number, of molecules of the compound. Balancing Equations – When balancing a chemical reaction you may add coefficients in front of the compounds to balance the reaction (get the same number of atoms of each element on both side of the equation. – You may not change the subscripts. • Changing the subscripts changes the compound. The subscripts are determined by the # of electrons needed to obtain an octet Chemical Equations 4Al(s) + 3O2(g)-->2Al2O3(s) This equation means 4 Al atoms + 3 O2 molecules ---produces---> 2 molecules of Al2O3 AND/OR 4 moles Al + 3 moles O2 ---produces---> 2 moles of Al2O3 Meaning of Chem Equation Steps to Balancing Equations There are four basic steps to balancing a chemical equation. 1. Write the correct formula for the reactants and the products. DO NOT TRY TO BALANCE IT YET! Once you write the formulas correctly DO NOT CHANGE them! 2. Determine the order of elements to use in order to balance the equation. Hints will follow. 3. Place coefficients in front of formulas so that the left side of the equation has the same number of atoms of each element as the right side of the equation. 4. Check your answer to see if: – The numbers of atoms of each element, on both each side of the equation should be the same. – The coefficients are in the lowest possible whole number ratio (reduced). Balancing Equations 2 H2(g) + ___ O2(g) ---> ___ 2 H2O(l) ___ What Happened to the Other Oxygen Atom????? This equation is not balanced! Two hydrogen atoms from a hydrogen molecule (H2) combines with one of the oxygen atoms from an oxygen molecule (O2) to form H2O. Then, the remaining oxygen atom combines with two more hydrogen atoms (from another H2 molecule) to make a second H2O molecule. Some Suggestions to Help You Some Helpful Hints for balancing equations: • Take one element at a time usually starting with the most complex substance. • It is usually better to balance in this order: metals, nonmetals, hydrogen, oxygen. • If everything balances except for O2, and there is no way to balance O2 with a whole number, use a fraction or mixed number. Then, multiply all coefficients by 2 to remove the fraction. • Polyatomic ions that appear on both sides of the equation should be balanced as whole units, not individual atoms. Balancing Equations 2 Al(s) + ___ 3 Br2(l) ---> ___ Al2Br6(s) ___ Balancing Equations 5 ____C3H8(g) + _____ O2(g) ---> 3 _____CO 2(g) 2 4H10(g) + ____B 2 B O (g) 4 __ 2 3 + 4 _____ H2O(g) 11 O (g) ----> 11/2 _____ 2 + 10 5 _____ H2O(g) Balancing Equations Sodium phosphate + iron (III) oxide sodium oxide + iron (III) phosphate 2 Na3PO4 + 3 Na2O Fe2O3 ----> + 2 FePO4 Balancing Chem Equations • Al + HCl --> AlCl3 • FeCl3 + Li2SO4 --> • Cu2S + Cu2O --> + H2 Fe2(SO4)3 + LiCl Cu • C3H8 + O2 --> H2O + CO2 • C2H6 + O2 --> H2O + CO2 + SO2 Type of Reactions Chemical reactions are classified into five general types Combination (synthesis) Decomposition (analysis) Single Displacement Double Displacement (metathesis) Combustion Types of Chemical Reactions 1. Combination or Synthesis Reaction: Two or more reactants combine to form (synthesize) one product. A+B AB 2Mg + O2 2MgO 2Na + Cl2 2NaCl CO2 + H2O H2CO3 DEMO Types of Chemical Reactions 2. Decomposition Reaction: A single substance is or broken down (decomposed) to give two or more different substances: AB A + B 2PbO2 2PbO + O2 2NaHCO3 Na2CO3 + H2O + CO2 2CuCO3 2CuO + CO2 2KClO3 2KCl + 3 O2 DEMO Quiz Classify the following reactions as 1) combination or 2) decomposition: ___A. H2 + Br2 2HBr ___B. Al2(CO3)3 Al2O3 + 3CO2 ___C. 4 Al + 3C Al4C3 Solution Classify the following reactions as 1) combination or 2) decomposition: _1_A. H2 + Br2 _2_B. Al2(CO3)3 _1_C. 4 Al + 3C 2HBr Al2O3 + 3CO2 Al4C3 Types of Chemical Reactions 3. Single Displacement Reaction: One element reacts with a compound to take the place of one of the elements of that compound. A + BC Zn + 2HCl Mg + 2CH3COOH Fe + CuSO4 B + AC H2 + ZnCl2 DEMO Zn(CH3COO)2 + H2 FeSO4 + Cu Types of Chemical Reactions • 4. Double Displacement or Metathesis: Two compounds exchange partners with each other to produce two different compounds. One product is in a different form (phase). AB + CD 2NaOH + Fe(NO3)2 Na2CO3 + CaCl2 ZnS + 2HCl AD + CB Fe(OH)2(s) + 2NaNO3 2NaCl + CaCO3(s) ZnCl2 + H2S(g) DEMO Quiz Classify the following reactions as 1) single displacement 2) double displacement A. 2Al + 3H2SO4 Al2(SO4)3 + 3H2 B. Na2SO4 + 2AgNO3 C. 3C + Fe2O3 Ag2SO4 + 2NaNO3 2Fe + 3CO Solution Classify the following reactions as 1) single replacement 2) double replacement 1 A. 2Al + 3H2SO4 Al2(SO4)3 + 3H2 2 B. Na2SO4 + 2AgNO3 1 C. 3C + Fe2O3 Ag2SO4 + 2NaNO3 2Fe + 3CO Types of Chemical Reactions • 5. Combustion All hydrocarbon (molecules containing C, H, and O) reacts with oxygen to form carbon dioxide and water HCO + O2 H2O + CO2 Combustion A reaction in which a compound (often carbon) reacts with oxygen CH4 + 2O2 C3H8 + 5O2 C6H12O6 + 6O2 CO2 + 2H2O 3CO2 + 4H2O 6CO2 + 6H2O Quiz Balance the combustion equations __C5H12 + __O2 __C4H10O + __O2 __ CO2 + __H2O __CO2 + __H2O Solution Balance the combustion equations 1 C5H12 + 8 O2 1 C4H10O + 6 O2 5 CO2 + 6 H2O 4 CO2 + 5 H2O Mol Factors And Energy changes In chemical equations Mole-Mole Factor Shows the mole-to-mole ratio between two of the substances in a balanced equation Derived from the coefficients of any two substances in the equation Writing Mole Factors Fe and O2 4 Fe + 4 mol Fe 3 mol O2 3 O2 2 Fe2O3 and 3 mol O2 4 mol Fe and 2 mol Fe2O3 4 mol Fe and 2 mol Fe2O3 3 mol O2 Fe and Fe2O3 4 mol Fe 2 mol Fe2O3 O2 and Fe2O3 3 mol O2 2 mol Fe2O3 Quiz 3 H2(g) + N2(g) 2 NH3(g) A. A mol factor for H2 and N2 is 1) 3 mol N2 2) 1 mol N2 1 mol H2 3) 1 mol N2 3 mol H2 2 mol H2 B. A mol factor for NH3 and H2 is 1) 1 mol H2 2) 2 mol NH3 3) 2 mol NH3 3 mol H2 3 mol N2 2 mol NH3 Solution 3 H2(g) + N2(g) 2 NH3(g) A. A mol factor for H2 and N2 is 2) 1 mol N2 3 mol H2 B. A mol factor for NH3 and H2 is 2) 2 mol NH3 3 mol H2 Chemical Calculations 4 Fe + 3 O2 2 Fe2O3 How many moles of Fe2O3 are produced when 6.0 moles O2 react? 6.0 mol O2 x 2 mol Fe2O3 = 4.0 mol Fe2O3 3 mol O2 Quiz 4 Fe + 3 O2 2 Fe2O3 How many moles of Fe are needed to react with 13.5 mol of O2? 1) 9.00 mol Fe 2) 10.1 mol Fe 3) 18.0 mol Fe Solution 4 Fe + 3 O2 2 Fe2O3 13.5 mol O2 x 4 mol Fe = 18.0 mol Fe 3 mol O2 End Mol : Energy Conversions 3 H2(g) + N2(g) 2 NH3(g) + 42 KJ The conversion factors for energy are 1) 3 mol H2 42 KJ 2) 1 mol N2 42 KJ 3) 2 mol NH3 42 KJ Quiz • How many KJ are given off by the reaction of 2.50 mol of H2 gas? 2.50 mol H2 42 KJ = 35.0 KJ 3 mol H2 Quiz • How many moles of ammonia are produced by a reaction that gives off 100 KJ of energy? 100 KJ 2 mol NH3 = 4.76 mol NH3 42 KJ Net Ionic Equations • NIE show – 1. Balance the formula equation – 2. Dissociate (pull apart) all (aq) compounds • Subscripts for R and P become coefficients • CaCl2(aq) Ca2+(aq) + 2Cl-(aq) – 3. Remove all spectator ions • spectator ions do nothing in the reaction and are excluded from the equation • NaOH(aq) + Cu(NO3)2(aq) --> NaNO3(aq) + Cu(OH)2(s) First, balance the equation 2NaOH(aq) + Cu(NO3)2(aq) --> 2NaNO3(aq) + Cu(OH)2(s) Write ionic eq (pull apart all aq compounds) and cancel the spectator ions 2Na+ + 2OH- + Cu2+ + 2NO3- --> 2Na+ + 2NO3- + Cu(OH)2(s) Write NIE (write (+) ion first) Cu2+(aq) + 2OH-(aq) ---> Cu(OH)2(s) This is all that really happened!!! Net Ionic Equations – BaCl2 and Na2SO4 are mixed. Write NIE for the reaction if a precipitate forms. • Ions present are Ba2+ Cl- Ag+ SO42- – Only + and - ions join together, therefore – Possible ppts are (Ba2 + and SO42-) or (Na+ and Cl-) » All chlorides are soluble (ex Ag+ and any Pb ion) » All sulfates are soluble (ex Ba2+) – Barium and sulfate ions will form a ppt Ba2+ + 2Cl- + 2Na+ + SO42- Ba+(aq) + SO42-(aq) BaSO4 (s) + 2Na+ + 2Cl- BaSO4(s) NIE from Reactants • Write NIE for any reaction (or no rx) that occurs when (aq) solutions of NaCl(aq) + AgNO3(aq) are mixed Na+ + Cl- + Ag+ + NO3- --> • possible ppt = AgCl or NaNO3 – All nitrate are soluble – Most Ag compounds are insoluble therefore ppt is – Ag+(aq) + Cl-(aq) AgCl(s) Al + HCl ---> AlCl3 + H2 • Cu2S + Cu2O ---> Cu + SO2 • WC + O2 ---> WO3 + CO2 • Al4C3 + H2O ---> Al(OH)3 + CH4 • TiCl4 + H2O ---> TiO2 + HCl • NH3 + O2 ---> N2 + H2O Review • Write NIE for any rx between aq sol’n of – AgNO3 (aq) + Ca(OH)2 (aq) – AlCl3 (aq) + Pb(NO3) 2 (aq) Energy Expressed as Mol Ratio • 2H2(g) + O2(g) 2H2O(l) + 572 kJ 2 mol H2 = 572 kJ therefore 2 mol H2 572 kJ or 572 kJ 2 mol H2 How many kJ of energy are given off when 12.0 mol of H2 is reacted with an excess of O2? • Convert 12.0 mol H2 to mol to kJ 12.0 mol H2 x 572 kJ = 2 mol H2