Chp 8 pg 240

A. Describing Chemical Reactions 1. Intro: a. Chem reaction – one or more substances is changed into one or more different substances b. Reactants – before reaction c. Products – after reaction

2. Indications of a Chemical Reaction a. Temperature change and light - Burning something b. Production of gas - Baking soda and vinegar c. Formation of a precipitate - Fig 8-2b pg 242 d. Color change - Rusting

3. Characteristics of Chemical Equations a. Equation must represent known facts b. Equation must contain correct formulas for reactants and products c. Conservation of mass is met 1) Balance your equation 2) Use coefficients

 CH 4 = Methane  NH 3 = Ammonia  CO 2 = Carbon dioxide  CaCO 3 = Calcium carbonate  SiO 2 = Sand (silicon dioxide)  NaF = Sodium fluoride  NaCl = Table salt  HCl = Hydrochloric acid  H 2 O = Water

 Hydrogen = H 2  Nitrogen = N 2  Oxygen = O 2  Fluorine = F 2  Chlorine = Cl 2  Bromine = Br 2  Iodine = I 2

6. Balancing Chemical Equations a. Has to follow conservation of mass b. Do this by adding coefficients c. Reactant elements must = product elements d. Steps 1) Work on one atom at a time 2) Start with elements that only appear once 3) H and O atoms should be done last

___H 2 O ___H 2 + ___O 2 _2_H 2 0 ___H 2 + ___O 2 _2_H 2 O _2_H 2 + __O 2

Zn + HCl ZnCl 2 + H 2 Al 4 C 3 + H 2 O CH 4 + Al(OH) 3

7. Word and Formula Equations a. Write the equation using words first b. Then put in symbols c. Balance equation Methane and oxygen methane + oxygen carbon dioxide + water CH 4 + O 2 CO 2 + H 2 O CH 4 + 2O 2 CO 2 + 2H 2 O

8. Additional symbols a. = yields b. = Reversible (products can reform reactants) c. ∆ = Reactants are heated d. Catalyst – speeds up reaction but is NOT used up

 Examples  3Fe(s) + 4H 2 O(g) Fe 3 O 4 (s) + O 2 (g)  2HgO ∆ 2Hg + O 2

 Write word and formula equations for the chemical reaction that occurs when solid sodium oxide is added to water at room temperature and forms sodium hydroxide. Make sure the formula is balanced.  Sodium oxide + water sodium hydroxide  Na 2 O + H 2 O NaOH

Solid calcium reacts with solid sulfur to produce solid calcium sulfide. Ca + S8 CaS Hydrogen gas reacts with fluorine gas to produce hydrogen fluoride gas. H2 + F2 HF

9. Significance of a Chemical Equation a. Coefficients indicate relative amounts of reactants and products b. Coefficients also represent moles H 2 + Cl 2 2HCl 1molecule H 2 : 1molecule Cl 2 : 2 molecules HCl 1mol H 2, 1 mol Cl 2, 2mol HCl

c. Relative masses can be determined from coefficients; use moles to convert to grams d. Reverse reaction has same relative amounts as forward reaction e. Don’t tell you: 1) If the reaction will happen 2) How fast the reaction will take place

1. Synthesis Reactions a. 2 or more substances combine to form a new compound b. A + X AX c. 2Mg + O 2 2MgO d. 2H 2 + O 2 2H 2 O

2. Decomposition Reaction a. Single compound broken down into simpler compound b. AX A +X c. 2H 2 O 2H 2 + O 2 d. Electrolysis – decomposition of substance by electric current

Demo pg 250

3. Single-Replacement Reaction a. 1 element replaces another b. A + BX AX + B c. 2Na + 2H2O 2NaOH +H 2 d. Mg + 2HCl H 2 + MgCl 2

4. Double Replacement Reaction a. 2 elements of a compound switch places b. Usually forms a precipitate, gas, or water c. AX + BY AY + BX d. FeS + 2HCl H 2 S + FeCl 2

5. Combustion Reactions a. Substance combines with oxygen releasing energy as light and heat b. Produces water vapor c. C 3 H 8 + 5O 2 3CO 2 +4H 2 O

d. Exothermic – gives off heat 6. Endothermic – absorbs heat

 Ethyl alcohol in bottle/jug  Zn in HCl w/ballon over beaker to catch gas – light balloon  Tennis ball canon