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Ch 8.1 Balancing Equations

Ch 8.1 Balancing Equations. Standard 3.a. : Students know how to describe chemical equations by writing balanced equations. Content Objective : We will know how to write word, formula, and chemical equations for chemical reactions and balance chemical equations.

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Ch 8.1 Balancing Equations

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  1. Ch 8.1 Balancing Equations • Standard 3.a.: Students know how to describe chemical equations by writing balanced equations. • Content Objective: We will know how to write word, formula, and chemical equations for chemical reactions and balance chemical equations. • Language Objective: I will write word, formula, and chemical equations for chemical reactions and balance chemical equations.

  2. Indications of a Chemical Reaction • Evolution of energy as heat and light. • Production of a gas • Formation of a precipitate • Color Change

  3. Characteristics of Chemical Equations • The equation must represent known facts. • The equation must contain the correct formulas for the reactants and products. • The law of conservation of mass must be satisfied.

  4. Chemical Reactions • Chemical equations give information in two major areas: 1. Reactants and products of the reaction. 2. Coefficients of a balanced chemical equation tell us the amount of the substances involved. Example: 2H2 (g) + O2 (g) 2H2O (g) Review: Reactants are on the left side of the arrow, and the products are on the right side. The arrow means “yields”, or “to produce”.

  5. Balancing Chemical Equations Why do you have to balance a chemical equation? • Law of Conservation of Matter (or Mass) • During a chemical reaction, atoms are either joined, separated, or rearranged. The number and type of each atom stays the same. How do you balance a chemical equation? • Coefficients 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.

  6. 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

  7. 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

  8. 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

  9. 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 Polyatomic ions 2 3 1 3 start over 2 2 2 1 Fix it 2 1 3

  10. Example • Aluminum is a good choice for outdoor furniture because it reacts with oxygen in the air to form a thin protective coat of aluminum oxide. Write word, formula, and chemical equations for this reaction. Aluminum + Oxygen  Aluminum Oxide Al(s) + O2(g)  Al2O3(s) 4Al(s) + 3O2(g)  2Al2O3(s)

  11. Homework • 8.1 page 274 #1-3 and page 290 #1-2, 13

  12. Ch 8.2: Five 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 “H,N,O,F,Cl,Br,I” elements are diatomic when alone!! • Remember to balance the equation after you write the products. + AX A X H2 O2 O2 KCl

  13. General Types of Reactions Synthesis two substances one compound 2) __________: (sometimes called Combination) • 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 Pb(OH)2

  14. General Types of Reactions (Continued) Combustion O2 CO2 H2O 3) _________________: Reacts with oxygen gas!!! • A reaction between a Carbon/Hydrogen with _____ always produces the same… ________ + ________ • This reaction is too easy!! Don’t miss it! General Form: CxHy + O2 ____ + ____ Examples: 2C2H2 + 5O2 _______ + _______ C7H6O + 8O2 _______ + _______ CO2 H2O 4CO2 2H2O 7CO2 3H2O

  15. General Types of Reactions (Continued) Single one compound one element compound element 4) _____________ Displacement: • A reaction between ____ ______________ and ___ ____________ that produces a different _____________ and ______________. General Forms: ____ + __  ____ + __ ____ + __  ____ + __ + AX Y AY X AX B BX A +

  16. General Types of Reactions (Continued) Double two compounds two compounds 5) _______________ Displacement: • 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: ____ + ____  ____ + ____ A solid produced during a chemical reaction is called a precipitate. Examples: CaCl2 (aq) + AgNO3 (aq) _________ + ________ NaOH (aq) + HCl (aq) ________ + ________ insoluble AX(aq) BY(aq) AY(aq) BX(s) + + Ca(NO3)2 AgCl (s) (aq) NaCl H2O (l) (aq)

  17. Double Displacement Reaction

  18. Homework 8.2 pg 284 #1-2 pg 291 #27 (write formulas, balance, and then classify!)

  19. Ch 8.2 and 8.3 Notes Types of Reactions and Activity Series

  20. Standard 3.a.: Students know how to describe chemical equations by writing balanced equations. • Content Objective: We will know how to determine products for the five types of reactions. • Language Objective: I will write the products of the chemical reaction and then balance the chemical reaction.

  21. Making Synthesis Reactions • Metals with nonmetals  ionic compounds Mg + O2  MgO • Nonmetals w/ nonmetals  covalent compounds C + O2  CO2 • Metal Oxides react with water to form Hydroxides CaO + H2O  Ca(OH)2 • Nonmetal Oxides react with water to form acids SO2 + H2O  H2SO3

  22. Decomposition • Decomposition of Binary Compounds HgO  Hg + O2 • Decomposition of Metal Carbonates CaCO3  CaO + CO2 • Decomposition of Metal Hydroxides Ca(OH)2  CaO + H2O • Decomposition of Metal Chlorates KClO3 KCl + O2 • Decomposition of Acids H2CO3 CO2 + H2O

  23. Combustion Remember, these ALWAYS produce CO2 and H2O!

  24. Single Displacement • The element that is trying to replace the other must be more reactive than the one it is replacing. • You must use the Activity Series to see if the reaction will happen. Page 286 Table 3 • The Higher up it is = the more reactive it is. • Elements from Li to Na can displace hydrogen in water to form a metallic hydroxide and H2 gas.

  25. 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

  26. Single Displacement Remember the Activity Series! • Metals Replace Metals Al + Pb(NO3)2 Pb + Al(NO3)3 • Metals Replace Hydrogen in Water Na + H2O  NaOH + H2 • Metals Replace Hydrogen in Acid Mg + HCl  H2 + MgCl2 • Halogens replace halogens below them

  27. Double Displacement • Switch the compounds and make sure the new compounds are balanced. KI + Pb(NO3)2 PbI2 + KNO3 • They will always react and switch, no activity series needed!

  28. Once you have solved for the products of the reaction, you must then BALANCE the reaction!

  29. Standard 3.a.: Students know how to describe chemical equations by writing balanced equations. • Content Objective: We will know how to determine products for the five types of reactions. • Language Objective: I will write the products of the chemical reaction and then balance the chemical reaction.

  30. Homework 8.2 page 284 #4 (solve for products, balance, and classify the reactions.) 8.3 page 287 #2-3 (In #2, predict which reactions will occur using activity series, then in #3, solve for the products for the ones that will occur and then balance.)

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