Chapter 8 Chemical Equations & Reactions

Chemical reactions  Chemical change: process by which one or more substances change to produce one or more different substances. –Different chemical and physical properties.  Reactants ---> products –Mass and atoms are conserved  Chemical change: process by which one or more substances change to produce one or more different substances. –Different chemical and physical properties.  Reactants ---> products –Mass and atoms are conserved

Evidence of a chemical reaction (pg 261, table 1)   E: released as heat, light, produce sound,  temperature and  in electrical E.  Formation of a new substance: formation of a gas, precipitate (s),  in color and release an odor.  Physical  is not a chemical . –Physical  :  state, evaporation, condensation, melting, freezing.   E: released as heat, light, produce sound,  temperature and  in electrical E.  Formation of a new substance: formation of a gas, precipitate (s),  in color and release an odor.  Physical  is not a chemical . –Physical  :  state, evaporation, condensation, melting, freezing.

Chemical equation  Representation of a chemical reaction that uses symbols to show the relationship between reactants and products.  Relative amounts of reactants and products.  Word equation: just the names of reactants and products, qualitative, not quantitative.  Balanced chemical equation: indicates quantitative amounts of reactants and products, states of each, temperature, pressure and net energy flow.  Representation of a chemical reaction that uses symbols to show the relationship between reactants and products.  Relative amounts of reactants and products.  Word equation: just the names of reactants and products, qualitative, not quantitative.  Balanced chemical equation: indicates quantitative amounts of reactants and products, states of each, temperature, pressure and net energy flow.

Word/chemical equation  Word equation:  Potassium chlorate decomposes to potassium chloride and oxygen  Chemical equation:  2KClO 3 (s) heat ->2KCl(s) + 3O 2 (g)  Additional reaction conditions (pg264, table 2): –(s), (l), (g), (aq), ---> (yield), (reversible reaction), --  --> (reactants heated), -- Pd --> (name of chemical acts as a catalyst)  Word equation:  Potassium chlorate decomposes to potassium chloride and oxygen  Chemical equation:  2KClO 3 (s) heat ->2KCl(s) + 3O 2 (g)  Additional reaction conditions (pg264, table 2): –(s), (l), (g), (aq), ---> (yield), (reversible reaction), --  --> (reactants heated), -- Pd --> (name of chemical acts as a catalyst)

Balancing chemical equations  Reactions conserve atoms: during reactions # and kinds of atoms are the same, they are just rearranged. (balanced)  Balance equations: –Subscripts for chemical formulas are determined by oxidation states and cannot be changed –# and type of atoms have to be equal on both sides of equations –----> “yield” sign also means equal –Balance equation with coefficients (small whole numbers in front of cpds) and can be changed until the reaction is balanced  Reactions conserve atoms: during reactions # and kinds of atoms are the same, they are just rearranged. (balanced)  Balance equations: –Subscripts for chemical formulas are determined by oxidation states and cannot be changed –# and type of atoms have to be equal on both sides of equations –----> “yield” sign also means equal –Balance equation with coefficients (small whole numbers in front of cpds) and can be changed until the reaction is balanced

Chemical equations  Steps to balance a chemical equation:  1. Identify reactants and products and write a correct formula for each (oxidation # and subscripts)  2. Count atoms and insert coefficients to balance.  3. Double check  Polyatomic ions that do not break apart can be counted as a single unit  Steps to balance a chemical equation:  1. Identify reactants and products and write a correct formula for each (oxidation # and subscripts)  2. Count atoms and insert coefficients to balance.  3. Double check  Polyatomic ions that do not break apart can be counted as a single unit

Balance chemical equations  Magnesium metal and water react to form magnesium hydroxide solution and hydrogen gas.  When ethane, C 2 H 6, gas burns it combines with oxygen to form carbon dioxide and water vapor.  Ag 2 O(s) --> Ag(s) + O 2 (g)  Al 2 O 3 (s) + C(s) --> Al(s) + CO 2 (g)  Mo 2 O 3 (s) + H 2 SO 4 (aq) + Zn(s) --> Mo 2 O 3 (s) + H 2 O(l) + ZnSO 4 (aq)  Magnesium metal and water react to form magnesium hydroxide solution and hydrogen gas.  When ethane, C 2 H 6, gas burns it combines with oxygen to form carbon dioxide and water vapor.  Ag 2 O(s) --> Ag(s) + O 2 (g)  Al 2 O 3 (s) + C(s) --> Al(s) + CO 2 (g)  Mo 2 O 3 (s) + H 2 SO 4 (aq) + Zn(s) --> Mo 2 O 3 (s) + H 2 O(l) + ZnSO 4 (aq)

Classifying chemical reactions  Reaction types: used to help predict products.  1. Combustion reaction: –Oxidation reaction of an organic cpd, heat is released. –Carbon-based cpd (hydrocarbon H, C and sometimes O) react with oxygen to form water and carbon dioxide.  2. Synthesis: reaction: –2 or more substances combine to form a new cpd. (one product) –A + X --> AX (binary or ternary cpd)  Reaction types: used to help predict products.  1. Combustion reaction: –Oxidation reaction of an organic cpd, heat is released. –Carbon-based cpd (hydrocarbon H, C and sometimes O) react with oxygen to form water and carbon dioxide.  2. Synthesis: reaction: –2 or more substances combine to form a new cpd. (one product) –A + X --> AX (binary or ternary cpd)

Classification of reactions cont.  Decomposition reaction: –Opposite of synthesis reaction. –Single cpd breaks down to form two or more simpler substances. –Usually endothermic (heat or electric current) –AX --> A + X  Predict and write a balanced equation: –A. pentane (C 5 H 12 ) reacting with oxygen –B. water reacting with potassium oxide –C. calcium reacting with oxygen –D. Decomposition of sodium chloride  Decomposition reaction: –Opposite of synthesis reaction. –Single cpd breaks down to form two or more simpler substances. –Usually endothermic (heat or electric current) –AX --> A + X  Predict and write a balanced equation: –A. pentane (C 5 H 12 ) reacting with oxygen –B. water reacting with potassium oxide –C. calcium reacting with oxygen –D. Decomposition of sodium chloride

Class. Cont. displacement Rx  Single displacement reaction: –Single element reacts with a cpd and displaces an element from the cpd –AX + Y --> AY + X or AX + B --> BX + A –Metal replaces metal, nonmetal replaces nonmetal –Activity series (pg 281 table 4): series of elements that have similar properties and arranged in descending order of chemical activity. –A more active element( single element) replaces a less active element ( in a cpd)  Single displacement reaction: –Single element reacts with a cpd and displaces an element from the cpd –AX + Y --> AY + X or AX + B --> BX + A –Metal replaces metal, nonmetal replaces nonmetal –Activity series (pg 281 table 4): series of elements that have similar properties and arranged in descending order of chemical activity. –A more active element( single element) replaces a less active element ( in a cpd)

Redox Reactions / Single Replacement Oxidation & reduction Defined Oxidation is the loss of electrons: OIL Ex: Zn is oxidized to Zn +2 Reduction is the gain of electrons: RIG Ex: Cu +2 is reduced to Cu In the following reaction identify which element is reduced and which element is oxidized. 2Al(s) + Fe 2 O 3 (s) --> 2Fe(l) + Al 2 O 3 (g)

Practice single displacement  Magnesium is dipped into a nickel (II) chloride solution  Lead is placed into an iron (III) nitrate solution  Zinc is added to a solution of copper (II) sulfate.  Magnesium is dipped into a nickel (II) chloride solution  Lead is placed into an iron (III) nitrate solution  Zinc is added to a solution of copper (II) sulfate.

Double displacement  An exchange of ions between two aqueous cpds in which a gas, solid or molecular cpd is formed  AX(aq) + BY(aq) --> AY + BX  One or both are either (s), (l) or (g)  Use solubility rules to determine the (s) ppt. –All cpd of group 1 and NH 4 + are soluble –All nitrates and acetates are soluble –All halides are soluble except Ag +, Pb 2+ and Hg 2 2+ –Alls sulfate sol except Ca 2+, Sr 2+, Ba 2+, Hg 2 2+ & Pb 2+ –Carbonates, hydroxides, phosphate are insol. except group 1 and NH 4 + cpds  An exchange of ions between two aqueous cpds in which a gas, solid or molecular cpd is formed  AX(aq) + BY(aq) --> AY + BX  One or both are either (s), (l) or (g)  Use solubility rules to determine the (s) ppt. –All cpd of group 1 and NH 4 + are soluble –All nitrates and acetates are soluble –All halides are soluble except Ag +, Pb 2+ and Hg 2 2+ –Alls sulfate sol except Ca 2+, Sr 2+, Ba 2+, Hg 2 2+ & Pb 2+ –Carbonates, hydroxides, phosphate are insol. except group 1 and NH 4 + cpds

Practice  Write and balance the following and label the type of reaction:  A. Solutions of silver acetate and calcium chloride are mixed  B. Lithium reacts with chlorine gas  C. Lithium carbonate is heated  D. Solutions of barium chloride and sodium sulfate are mixed.  E. Magnesium metal is added to hydrochloric acid  F. Propanol (C 3 H 7 OH) is burned in air  Write and balance the following and label the type of reaction:  A. Solutions of silver acetate and calcium chloride are mixed  B. Lithium reacts with chlorine gas  C. Lithium carbonate is heated  D. Solutions of barium chloride and sodium sulfate are mixed.  E. Magnesium metal is added to hydrochloric acid  F. Propanol (C 3 H 7 OH) is burned in air

Net ionic equations  Equation that quantitatively represents those atoms, ions or molecules that undergo a chemical change.  Spectator ions: ions that are present in a solution in which they do not participate in the chemical change  Writing net ionic equations: –Write a balance equation indicating the phase of each product –Remove spectators ions, indicate # of ions or products, state and oxidation #. (use sol. rules to determine ppt) –# and type of atoms must be balanced.  Equation that quantitatively represents those atoms, ions or molecules that undergo a chemical change.  Spectator ions: ions that are present in a solution in which they do not participate in the chemical change  Writing net ionic equations: –Write a balance equation indicating the phase of each product –Remove spectators ions, indicate # of ions or products, state and oxidation #. (use sol. rules to determine ppt) –# and type of atoms must be balanced.

Practice  A. Solutions of calcium hydroxide and hydrochloric acid are mixed.  B. Solutions of silver nitrate and potassium bromide are mixed  C. Lead (II) acetate and sodium sulfate solutions are combined.  A. Solutions of calcium hydroxide and hydrochloric acid are mixed.  B. Solutions of silver nitrate and potassium bromide are mixed  C. Lead (II) acetate and sodium sulfate solutions are combined.