Ch. 8 Chemical Reactions I. Intro to Reactions (p. 241 250) I II III IV V
APPETIZER Below is a chemical equation representing the decomposition reaction of ammonium dichromate into nitrogen chromium (III) oxide, and water. (NH 4 ) 2 Cr 2 O 7 (s) ----> N 2 (g) + Cr 2 O 3 (s) + 4H 2 O(g)
APPETIZER KEY idea: In a chemical reaction, new compounds are formed by bonds being broken, atoms rearranging, and new bonds forming. (NH 4 ) 2 Cr 2 O 7 (s) ----> N 2 (g) + Cr 2 O 3 (s) + 4H 2 O(g)
APPETIZER Can you think of any chemical reactions that you come in contact with on a daily basis? Pharaoh s Serpent
A.Signs of a Chemical Reaction Evolution of heat and light Formation of a gas Color change Formation of a precipitate
B.Law of Conservation of Mass mass is neither created nor destroyed in a chemical reaction total mass stays the same atoms can only rearrange 4 H 2 O 36 g 4 H 2 O 4 g 32 g
C. Chemical Equations A+B C+D REACTANTS PRODUCTS
D. Writing Equations 2H 2 (g) + O 2 (g) 2H 2 O(g) Identify the substances involved. Use symbols to show: How many? - coefficient Of what? - chemical formula In what state? - physical state Remember the diatomic elements.
C. Chemical Equations p. 246
D. Writing Equations Two atoms of aluminum react with three units of aqueous copper(ii) chloride to produce three atoms of copper and two units of aqueous aluminum chloride. How many? Of what? In what state? 2 Al (s) + 3 CuCl 2 (aq) 3 Cu (s) + 2 AlCl 3 (aq)
E. Describing Equations Describing Coefficients: individual atom = atom covalent substance = molecule ionic substance = unit 3CO 2 2Mg 4MgO 3 molecules of carbon dioxide 2 atoms of magnesium 4 units of magnesium oxide
E. Describing Equations Zn(s) + 2HCl(aq) ZnCl 2 (aq) + H 2 (g) How many? Of what? In what state? One atom of solid zinc reacts with two molecules of aqueous hydrogen chloride (hydrochloric acid) to produce one unit of aqueous zinc chloride and one molecule of hydrogen gas.
Ch. 8 Chemical Reactions II. Balancing Equations (p. 250-254) I II III IV V
Appetizer: What is wrong with these two pictures?
A. Balancing Steps 1. Write the unbalanced equation. 2. Count atoms on each side. 3. Add coefficients to make #s equal. Coefficient subscript = # of atoms 4. Reduce coefficients to lowest possible ratio, if necessary. 5. Double check atom balance!!!
B. Helpful Tips Balance one element at a time. Update ALL atom counts after adding a coefficient. If an element appears more than once per side, balance it last. Balance polyatomic ions as single units. 1 SO 4 instead of 1 S and 4 O
C. Balancing Example Aluminum and copper(ii) chloride react to form copper and aluminum chloride. 2 Al + 3 CuCl 2 3 Cu + 2 AlCl 3 2 1 Al 1 2 3 1 Cu 1 3 6 2 Cl 3 6
E2 C 8 H 18 + O 2 CO 2 + H 2 O
E3 Aluminum sulfate solution and calcium hydroxide solution produce a precipitate of aluminum hydroxide and solid calcium sulfate.
E4 FeS + O 2 Fe 2 O 3 + SO 2
Ch. 8 Chemical Reactions III. Types of Chemical Reactions (p. 256-267) I II III IV V
A. Combustion the burning of any substance in O 2 to produce heat A + O 2 B CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(g)
A. Combustion Products: contain oxygen hydrocarbons form CO 2 + H 2 O 4 Na(s)+ O 2 (g) 2 Na 2 O(s) C 3 H 8 (g)+ 5 O 2 (g) 3 CO 2 (g)+ 4 H 2 O(g)
B. Synthesis the combination of 2 or more substances to form a compound only one product A + B AB
Synthesis Reaction +
B. Synthesis H 2 (g) + Cl 2 (g) 2 HCl(g)
B. Synthesis Products: ionic - cancel charges covalent - hard to tell Al(s)+ Cl 2 (g) AlCl 3 (s) 2 3 2
C. Decomposition a compound breaks down into 2 or more simpler substances only one reactant AB A + B
Decompostion Reaction +
C. Decomposition 2 H 2 O(l) 2 H 2 (g) + O 2 (g)
C. Decomposition Products: binary - break into elements others - hard to tell KBr(l) K(s) + Br 2 (l) 2 2
The Activity Series of Metals Higher activity Lower activity 32 Lithium Potassium Calcium Sodium Magnesium Aluminum Zinc Chromium Iron Nickel Lead Hydrogen Bismuth Copper Mercury Silver Platinum Gold 1) Metals can replace other metals, provided they are above the metal they are trying to replace (for example, zinc will replace lead) 2) Metals above hydrogen can replace hydrogen in acids. 3) Metals from sodium upward can replace hydrogen in water.
The Activity Series of Halogens Higher Activity Fluorine Chlorine Bromine Iodine Lower Activity Halogens can replace other halogens in compounds, provided they are above the halogen they are trying to replace. 2NaCl (s) + F 2(g) 2NaF??? (s) + Cl 2(g) MgCl 2(s) + Br 2(g) No??? Reaction! 33
D. Single Displacement one element replaces another in a compound metal replaces metal (+) nonmetal replaces nonmetal (-) A + BC B + AC
D. Single displacement Cu(s) + 2AgNO 3 (aq) Cu(NO 3 ) 2 (aq) + 2Ag(s)
D. Single Replacement Products: metal metal (+) nonmetal nonmetal (-) free element must be more active (check activity series) Fe(s)+ CuSO 4 (aq) Cu(s)+ FeSO 4 (aq) Br 2 (l)+ NaCl(aq) N.R.
E. Double Displacement ions in two compounds change partners cation of one compound combines with anion of the other AB + CD AD + CB
E. Double Displacement Pb(NO 3 ) 2 (aq) + K 2 CrO 4 (aq) PbCrO 4 (s) + 2KNO 3 (aq)
E. Double Displacement Products: switch negative ions one product must be insoluble (check solubility table) Pb(NO 3 ) 2 (aq)+ 2 KI(aq) PbI 2 (s)+ 2 KNO 3 (aq) NaNO 3 (aq)+ KI(aq) N.R.
Ch. 17 Chemical Reactions IV. Reaction Energy (p. 514-517) I II III IV V
A. Reaction Pathway Shows the change in energy during a chemical reaction
B. Exothermic Reaction reaction that releases energy products have lower PE than reactants energy released 2H 2 (l) + O 2 (l) 2H 2 O(g) + energy
C. Endothermic Reaction reaction that absorbs energy reactants have lower PE than products energy absorbed 2Al 2 O 3 + energy 4Al + 3O 2
Ch. 17 Chemical Reactions V. Reaction Rate (p. 532-541) I II III IV V
A. Collision Theory Reaction rate depends on the collisions between reacting particles. Successful collisions occur if the particles... collide with each other have the correct orientation have enough kinetic energy to break bonds
A. Collision Theory Particle Orientation Required Orientation Successful Collision Unsuccessful Collisions
A. Collision Theory Activation Energy (E a ) minimum energy required for a reaction to occur Activation Energy
A. Collision Theory Activation Energy depends on reactants low E a = fast rxn rate E a
B. Factors Affecting Rxn Rate Surface Area high SA = fast rxn rate more opportunities for collisions Increase surface area by - using smaller particles - dissolving in water
B. Factors Affecting Rxn Rate Concentration high conc = fast rxn rate more opportunities for collisions
B. Factors Affecting Rxn Rate Temperature high temp = fast rxn rate high KE - fast-moving particles - more likely to reach activation energy
B. Factors Affecting Rxn Rate Temperature Analogy: 2-car collision 5 mph fender bender 50 mph high-speed crash
B. Factors Affecting Rxn Rate Catalyst substance that increases rxn rate without being consumed in the rxn lowers the activation energy
B. Factors Affecting Rxn Rate Enzyme Catalysis