CHEMICAL REACTIONS AND EQUATIONS Unit 5 Notes

Unit 5 Notes: Part 1 Types of Reactions Chemical Reactions occur when bonds between atoms are formed or broken. Indications that a chemical reaction has occurred:  Color change  Gas production (bubbles)  Precipitate formed (solid formed from 2 liquids)  Temperature change

Indications that a chemical reaction has occurred: Gas production:  e e Precipitate: &safe=active &safe=active Temperature change:  RhQM4DHV4c&safe=active RhQM4DHV4c&safe=active Color change (precipitate): 

What is a chemical equation? Chemical Symbols: represent elements: Mg, S Chemical Formulas: represent compounds: MgS Chemical Equations: represent reactions: Mg + S MgS (reactants)(products) Chemical reactions begin with reactants and end with products.

Symbols used in Equations: Solid (s) Liquid ( l ) Gas (g) Aqueous solution (aq) Catalyst H2SO4 Escaping gas ( ) Change of temperature ( )

5 types of Chemical Reactions: 1.Synthesis: substances combine to form one compound  A + X AX  2H 2 + O 2 2H 2 O Practice predicting the products: a.sodium metal reacts with chlorine gas b.solid magnesium reacts with fluorine gas

5 types of Chemical Reactions: 2.Decomposition: compounds break down into smaller compounds and/or single elements  AX A + X  2H 2 O 2H 2 + O 2 Practice predicting the products: a.solid lead (IV) oxide decomposes: b.aluminum nitride decomposes:

5 types of Chemical Reactions: Decomposition exceptions: Carbonates and chlorates do not decompose into single elements. Carbonates decompose to carbon dioxide and a metal oxide. CaCO 3 CO 2 + CaO Chlorates decompose to oxygen gas and a metal chloride 2Al(ClO 3 ) 3 9O 2 + 2AlCl 3

5 types of Chemical Reactions: 3.Single Replacement Reactions: when one element replaces another in a compound; metal replaces metal; nonmetal replaces nonmetal  A + BX AX + B (metal replaces metal)  Y + BX BY + X (nonmetal replaces nonmetal)  2Al + 3Pb(NO 3 ) 2 3Pb + 2Al(NO 3 ) 3 Practice: a.Zinc metal reacts with aqueous hydrochloric acid b.Sodium chloride solid reacts with fluorine gas

5 types of Chemical Reactions: 4.Double Replacement Reactions: two compounds either trade metals or trade nonmetals  AX + BYAY + BX  2KI + Pb(NO 3 ) 2 PbI 2 + 2KNO 3 Practice: a. HCl(aq) + AgNO 3 (aq) b. CaCl 2 (aq) + Na 3 PO 4 (aq) c. Pb(NO 3 ) 2 (aq) + BaCl 2 (aq) d. FeCl 3 (aq) + NaOH(aq) e. H 2 SO 4 (aq) + NaOH(aq) f.KOH(aq) +CuSO 4 (aq)

5 types of Chemical Reactions: 5.Combustion Reactions: occurs when a hydrocarbon reacts with oxygen gas; products are always CO 2 and H 2 O Practice: a. C 5 H 12 + O 2 b. C 10 H 22 + O 2

Mixed Practice: ID the type of reaction, predict the products, balance a. BaCl 2 +H 2 SO 4 b. C 6 H 12 +O 2 c. Zn+CuSO 4 d. Cs+Br 2 e. FeCO 3

Part 2: Balancing Equations Law of Conservation of Matter:matter cannot be created or destroyed When a chemical reaction occurs, the amount of Reactants must equal the amount of products. If an equation does not have equal numbers of atoms on each side, it is not balanced. To balance an equation, use coefficients which are numbers in front of a symbol or formula. NEVER change the subscripts!!

Part 2: Balancing Equations Al (s) + O 2 (g) Al 2 O 3 (s) What is wrong with this equation? Fix it with coefficients! The final equation has 1 meanings: 4 atoms of Al + 3 molecules of O 2 yield 2 molecules of Al 2 O 3

Practice Balancing Equations: 1. H 2 (g) + O 2 (g) H 2 O(l) 2. C 3 H 8 (g) + O 2 CO 2 (g) + H 2 O 3. B 4 H 10 (g) + O 2 (g) B 2 O 3 (g) + H 2 O(l)

Practice Balancing Equations: 4. sodium phosphate + iron (III) oxide sodium oxide + iron (III) phosphate 5. sodium chloride + silver nitrate sodium nitrate + silver chloride 6.Iron (III) hydroxide iron (III) oxide + water

Practice Balancing Equations: 7. radium phosphide + sodium sodium phosphide + radium 8.cesium + sulfur cesium sulfide 9.potassium metal + chlorine gas potassium chloride

Practice Balancing Equations: Diatomic molecules are atoms that always occur in pairs and should be written as pairs in equations:

Part 4: Energy Involved in Chemical Reactions: Endothermic Reactions: Exothermic Reactions:

Part 5: Activity Series: In single replacement reactions you have to use an activity series to determine if an element can replace another: Li(More reactive) Mg Al Zn Cr Fe Pb H Cu Hg(Less reactive) Au

Part 5: Activity Series: Elements can replace other elements that are more reactive (top can replace bottom) Example: Pb 2 O 3 + Cu à These substance won’t react with each other. The copper is not strong enough or “active” enough to replace the lead.

Part 5: Activity Series: In addition to more active metals replacing less active metals, nonmetals can also replace other nonmetals (Most reactive at top…fluorine) Practice: a. FeO 2 +Cr à b. FeS+Hg à c. ZnCl 2 +H 2 à