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Ch. 7 & 8 Notes -- Chemical Reactions

Ch. 7 & 8 Notes -- Chemical Reactions. Reactants. products. amount. Chemical equations give information in two major areas: 1. _____________ and ______________ of the reaction. 2. Coefficients of a balanced chemical equation tell us the ______ of the substances involved.

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Ch. 7 & 8 Notes -- Chemical Reactions

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  1. Ch. 7 & 8 Notes -- Chemical Reactions Reactants products amount • Chemical equations give information in two major areas: 1. _____________ and ______________ of the reaction. 2. Coefficients of a balanced chemical equation tell us the ______ of the substances involved. Example of a Balanced Chemical Equation: 2H2 (g) + O2 (g) 2H2O (g) Review: Reactants are on the ______ side of the arrow, and the products are on the __________ side. The arrow means “________”, or “reacts to produce” when read aloud. • From our example, hydrogen reacts with oxygen in a ___:___ ratio. • The coefficients represent either the number of _________ or molecules present. • The coefficients can also represent _________ if the substances are gases. (1 mole = 6.02 x 1023 molecules, 1 mole of gas= 22.4 Liters) left right yields 2 1 moles liters

  2. Common Symbols used in Chemical Equations + = used to separate 2 reactants or 2 products from each other →= “yields” or “reacts to produce” = _____________ reaction (like a rechargeable battery) (s) (l) (g) (aq) = phase of matter: (solid, liquid, gas, or “aqueous”) = ___________ supplied to the reaction MnO2 = a catalyst, (in this case, MnO2), is used to ________ ____ the reaction. = _______ given off as a product = ______ precipitate produced reversible heat speed up gas solid

  3. Decoding Common Chemical Equation Symbols PracticeProblems: Describe the following reactions using complete sentences. a) NaHCO3(s) + HCl (aq)NaCl (aq) + H2O (l) + CO2 b) H2SO4(aq) + BaCl2(aq) HCl (aq) + BaSO4(s) c) Write a chemical equation from the following description: “Sodium plus bromine, when heated, reacts to produce solid sodium bromide.” Solid sodium bicarbonate plus aqueous hydrochloric acid yields aqueous sodium chloride plus water plus carbon dioxide gas. Aqueous sulfuric acid plus aqueous barium chloride yields aqueous hydrochloric acid plus solid barium sulfate. + Br2  NaBr (s) Na (s) (l)

  4. Balancing Chemical Equations • Why do you have to balance a chemical equation? • Law of Conservation of Matter (or Mass): “Matter is neither ____________ nor _______________ in chemical reactions.” • During a chemical reaction, atoms are either _________, ______________, or rearranged. The _____________ and type of each atom stays the same. • How do you balance a chemical equation? • __________________ are placed in front of the substances involved in the chemical reaction to get the same number of atoms of each element on both sides of the equation. This number will multiply the number of atoms there are in a formula. created destroyed joined separated number Coefficients

  5. Rules for Balancing Chemical Equations in front (1) Coefficients can only be placed ___ _________ of a chemical formula. Practice Problems: How many atoms of each type are indicated in the following compounds? (a) 2 (NH4)3PO4 N= ___ H= ___ P= ___ O= ___ (b) 4 KC2H3O2 K= ___ C= ___ H= ___ O= ___ (c) 3 Ca(NO3)2 Ca= ___ N= ___ O= ___ 6 24 2 8 4 8 12 8 3 6 18

  6. Rules for Balancing Chemical Equations subscript 2 2 (2) You cannot change a ________________!! Example : H2 + O2 H2O To balance oxygen, you cannot change water’s formula to_________! (3) You cannot place the coefficient in the ______________ of a formula!! Example : Al + N2 AlN To balance nitrogen, you cannot put a 2 in the middle to make _______. (4) Reduce the coefficients to the simplest ____________ ___ ratio. Example: 4H2 + 2O2 4H2O can be reduced to… __H2 + __O2 __H2O H2O2 middle 2 2 Al2N whole # 2 1 2

  7. Rules for Balancing Chemical Equations fractions whole fraction (5) Get rid of any ____________! Coefficients must be _________ #’s • You can’t have a _______________ of a molecule or atom! Example: 1H2 + ½O2 1H2O changes to… __ H2 + __O2 __H2O 2 x ( ) 2 1 2

  8. Balancing Equations: “Helpful Hints” last 1 2 1 1 a) Balance elements that appear in more than one compound ________. ___(NH4)2CO3 ___NH3 + ___CO2 + ___H2O b) Balance _____ “___________” as though it were one item as long as the ion stays together as a group on each side of the yields arrow. ___Al + ___CuSO4 ___Al2(SO4)3 + ___Cu c) If you can’t seem to get it balanced, _________ _________ and begin with a different element the next time, or put a “2” somewhere and then try again. ___Li + ___H2O  ___LiOH + ___H2 • This is what I’ll constantly be telling you to do if you are stuck and you need my help... “Pick an element to balance. How many are on the left side? How many are on the right side? ________ ____!” ___Fe(OH)3 ___Fe2O3 + ___H2O ion chunks 2 3 1 3 start over 2 2 2 1 Fix it 2 1 3

  9. Balancing Equations: “Helpful Hints” 2 3 3 2 e) My goofy “balancing song” may help: “If there’s a ___ on the left and a ___on the right, you put a ___ on the left and a ___ on the right, (makin’ money!)” ___Al + ___O2 ___Al2O3 f) If you see only C’s H’s and O’s, balance them in this order: C, H, O. ___C2H2 + ___O2 ___CO2 + ___H2O ___C2H2 + ___O2 ___CO2 + ___H2O 4 3 2 2 x ( ) 1 5/2 2 1 2 5 4 2

  10. Five General Types of Reactions Decomposition one compound 1) ________________________: • A reaction that breaks apart ______ ______________ into simpler substances, (usually two elements or an element and a smaller compound.) General Form: _____  ___ + ___ Examples: H2O  _____ + _____ KClO3 _____ + _____ Remember that “HONClBrIF” elements are diatomic when alone!! + AX A X H2 O2 O2 KCl

  11. Categories of Decomposition (and Composition ) Reactions CaO CO2 NaCl O2 a) carbonates  metallic oxide + CO2CaCO3 _____ + _____ b) chlorates  metallic chloride + O2NaClO3 _____ + _____ c) hydroxides  metallic oxide + H2O Mg(OH)2 _____ + _____ d) oxy acids  nonmetal oxide + H2O H2SO4 _____ + _____ e) binary compounds  2 elements NaCl  _____ + _____ • Every time you try to write the formula for a new compound, you must look up the ___________ of the ions and ___________ them if they are different!! • Balance it _________ you get all the correct formulas written first! • Don’t forget about the HONClBrIF’s! MgO H2O SO3 H2O Na Cl2 charges cross AFTER

  12. General Types of Reactions (Continued) Composition two substances one compound 2) _______________: (sometimes called “Combination” or “Synthesis”) • A reaction of _____ __________________, typically a metal and a nonmetal to form ______ ______________. • It is the opposite of decomposition. (The same categories of reactions from above apply, just in reverse.) General Form: ___ + ___  _____ Examples: Al + Cl2 _______ PbO + H2O  ______ + A X AX AlCl3 2 elements binary compound Pb(OH)2 metallic + water oxide  hydroxide

  13. General Types of Reactions (Continued) Single one compound one element compound element 3) _____________ Replacement: • A reaction between ____ ______________ and ___ ____________ that produces a different _____________ and ______________. General Forms: ____ + __  ____ + __ ____ + __  ____ + __ • The element that is trying to replace the other must be ________ _______________ than the one it is replacing. • You must use the Activity Series to see if the reaction will happen. • _________ ___ = more reactive • Elements from ____ to ____ can displace hydrogen in water to form a metallic hydroxide and H2 gas. + AX Y AY X AX B BX A + more reactive Higher up Li Na

  14. Activity Series

  15. Single Replacement Reactions NaF Cl2 Examples: NaCl + F2 _____ + _____ FeCl2 + K  _____ + _____ HCl + Zn  _____ + _____ HCl + Au  _____ + _____ H2O + Na  _____ + _____ H2O + Fe  _____ + _____ AgNO3 + Cu  _____ + _____ KCl Fe ZnCl2 H2 no reaction H2 NaOH H(OH) no reaction CuNO3 Ag

  16. General Types of Reactions (Continued) Double two compounds two compounds 4) _______________ Replacement: (sometimes called “Ionic”) • A reaction between _____ ________________ that are dissolved in water that produces _____ ________________ , one of which is ________________. • Water or a gas may be one of the two compounds being produced. General Form: ____ + ____  ____ + ____ • You must use the SolubilityChart to see which product is the precipitate. • Solubility Chart Key ___ or _____= precipitate Examples: CaCl2 (aq) + AgNO3 (aq) _________ + ________ NaOH (aq) + HCl (aq) ________ + ________ insoluble AX(aq) BY(aq) AY(aq) BX(s) + + I sS Ca(NO3)2 (aq) AgCl (aq) NaCl H2O (l)

  17. Double Replacement Reaction

  18. General Types of Reactions (Continued) Combustion O2 compound 5) _________________: • A reaction between a Carbon/Hydrogen (and sometimes Oxygen) _________________ with _____. • The products are always the same… ________ + ________ • This reaction is too easy!! Don’t miss it! General Form: CxHy + O2 ____ + ____ Examples: C2H2 + O2 _______ + _______ C7H6O + O2 _______ + _______ CO2 H2O CO2 H2O CO2 H2O CO2 H2O

  19. Writing Net Ionic Equations for Double Replacement Reactions ions • A “net ionic equation” only shows the _________ that were used to make the precipitate. • Some ions were always dissolved in water. These are called “________________ ions”. (They don’t do anything, so we can ignore them.) Example: CaCl2 (aq) + 2AgNO3(aq) Ca(NO3)2(aq) + 2AgCl (s) IonicEquation Written as Ions Dissolved in Water: ___ (aq) + ___ (aq) + ___ (aq) + _____ (aq) ___ (aq) + _____ (aq) + _________(s) • Cancel out the spectator ions, and you are left with the Net Ionic Equation! ________ + _________  __________ spectator Ca+2 2Cl− 2Ag+ 2NO3 − Ca+2 2NO3 − 2AgCl 2Cl−(aq) 2Ag+(aq) 2AgCl(s)

  20. Writing Net Ionic Equations for Double Replacement Reactions KNO3 (aq) BaCO3 Practice Problem: Write the net ionic equation for the following reaction. K2CO3(aq) + Ba(NO3)2(aq) _________ + _________ Net Ionic Equation = ____________________________________ CO3 −2 (aq) + Ba+2(aq) BaCO3

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