CHEMICAL REACTIONS

Chemical Reactions A process by which the atoms of one or more substances are rearranged to form different substances A process by which the atoms of one or more substances are rearranged to form different substances Indications that a chemical reaction has occurred are: Indications that a chemical reaction has occurred are: Permanent color change Permanent color change Production of a new solid (precipitate) Production of a new solid (precipitate) Production of a new gas Production of a new gas Release of heat, light or sparks Release of heat, light or sparks

Word & Skeleton Equations WORD EQUATIONS: WORD EQUATIONS: Use words and statements to indicate the reactants and products of a reaction. Use words and statements to indicate the reactants and products of a reaction. Example: Example: iron (s) + chlorine (g)  iron(III)chloride (s) iron (s) + chlorine (g)  iron(III)chloride (s) Read “Solid Iron and chlorine gas react to produce solid iron (III) chloride” Read “Solid Iron and chlorine gas react to produce solid iron (III) chloride” SKELETON EQUATIONS: SKELETON EQUATIONS: Uses chemical formulas rather than words to identify the reactants and products of a chemical reaction. Uses chemical formulas rather than words to identify the reactants and products of a chemical reaction. Example: Example: WORD EQUATION: iron (s) + chlorine (g)  iron (III) chloride (s) WORD EQUATION: iron (s) + chlorine (g)  iron (III) chloride (s) SKELETON EQUATION: Fe (s) + Cl 2(g)  FeCl 3(s) SKELETON EQUATION: Fe (s) + Cl 2(g)  FeCl 3(s)

Chemical Equation Statement that uses chemical formulas to show the identities and relative amounts of the substances involved in a chemical reaction Statement that uses chemical formulas to show the identities and relative amounts of the substances involved in a chemical reaction Example: Example: WORD EQUATION: iron (s) + chlorine (g)  iron(III)chloride (s) WORD EQUATION: iron (s) + chlorine (g)  iron(III)chloride (s) SKELETON EQUATION: Fe (s) + Cl 2(g)  FeCl 3(s) SKELETON EQUATION: Fe (s) + Cl 2(g)  FeCl 3(s) CHEMICAL EQUATION: 2Fe (s) + 3Cl 2(g)  2FeCl 3(s) CHEMICAL EQUATION: 2Fe (s) + 3Cl 2(g)  2FeCl 3(s) 2Fe + 3Cl 2  2FeCl 3 + 

Parts of a Reaction Reactants Reactants The substances that combine together (or react) The substances that combine together (or react) Products Products The new substances created or produced by the rearrangement of atoms in the reactants The new substances created or produced by the rearrangement of atoms in the reactants H 2 (g) + 2O 2 (g)  2H 2 O (l)

Parts of a Reaction Symbols to know Symbols to know (cr) = solid (cr) = solid (g) = gas (g) = gas (l) = liquid (l) = liquid (aq) solid dissolved in water (aq) solid dissolved in water ↓ = precipitate forms ↓ = precipitate forms ↑ = gas forms ↑ = gas forms Subscripts Subscripts Number of atoms Number of atoms Coefficients Coefficients Number of molecules of compound Number of molecules of compound H 2 (g) + 2O 2 (g)  2H 2 O (l)

Parts of a Reaction  (Yield symbol)  (Yield symbol) Reads as“to produce” or “yields” Reads as“to produce” or “yields” + (on the reactant side) + (on the reactant side) Reads as “reacts with” Reads as “reacts with” + (on the products side) + (on the products side) Reads as“and” Reads as“and” H 2 (g) + 2O 2 (g)  2H 2 O (l)

Types of Chemical Reactions Synthesis Synthesis Two or more reactants combine to form one new product Two or more reactants combine to form one new product A + B  AB A + B  AB Decomposition Decomposition When one reactant breaks down into two or more products When one reactant breaks down into two or more products AB  A + B AB  A + B +  2Na + Cl 2  2NaCl 2H 2 O  2H 2 + O 2  +

Types of Chemical Reactions Single Displacement Single Displacement When one ion replaces another of a like charge When one ion replaces another of a like charge AB + C  AC + B AB + C  AC + B Activity Series Activity Series Li Li K Ca Ca Na Na Mg Mg Al Al Zn Zn +  + 2Li + 2H 2 O  2LiOH + H 2

Types of Chemical Reactions Double Displacement Double Displacement When the positive (+) ion of one compound replaces the positive (+) ion of another compound to form two new compounds When the positive (+) ion of one compound replaces the positive (+) ion of another compound to form two new compounds AB + CD  AD + CB AB + CD  AD + CB Ca(OH) 2 + 2HCl  CaCl 2 + 2H 2 O +  +

Types of Chemical Reactions Combustion Combustion An element or a compound reacts with oxygen, often producing energy in the form of heat and light. An element or a compound reacts with oxygen, often producing energy in the form of heat and light. Ex. Ex. CH 4(g) + 2O 2(g)  CO 2(g) + 2H 2 O (g) +  +

Law of Conservation of Mass/Matter CONSERVATION OF MASS CONSERVATION OF MASS Matter cannot be created nor destroyed… it can only be rearranged! Matter cannot be created nor destroyed… it can only be rearranged! In reactions In reactions The total mass of the reactants must equal the total mass of the products The total mass of the reactants must equal the total mass of the products Due to the conservation of mass/matter… Due to the conservation of mass/matter… ALL CHEMICAL EQUATIONS MUST BE BALANCED!!!

Balancing Reactions There are 4 rules for balancing chemical equations: There are 4 rules for balancing chemical equations: Once you have written the chemical formulas for the compounds you… Once you have written the chemical formulas for the compounds you…  CANNOT change SUBSCRIPTS  CAN ONLY change COEFFICIENTS  Use the LOWEST RATIOS  If the same polyatomic ion is on both sides of the equation, treat it like you would any other atom

Steps for Balancing Chemical Reactions  Write the skeleton equation  Make a product/reactant chart -- List the atoms on each side individually -- Using subscripts & coefficients, determine how many of each atom exists  Balance the equation by changing coefficients  Reduce coefficients

EXAMPLES OF BALANCING… Na + I 2  NaI Na = 1 I = 2 Na = 1 I = 1 Does not equal, so… you must add coefficients… 22 Na = 1 I = 2 Na = 1 I = 1 X2 X2 X2 THE EQUATION IS NOW BALANCED!!

EXAMPLES OF BALANCING… CH 4 + O 2  CO 2 + H 2 O C = 1 H = 4 C = 1 H = 2 Does not equal, so… you must add coefficients… 2 2 THE EQUATION IS NOW BALANCED!! O = 2 O = 3 C = 1 H = 4 C = 1 H = 2 O = 2 O = 3 X4 X4 X4

Balancing Practice Balancing Practice CaCO 3  CaO + CO 2 N 2 + H 2  NH 3 CH 4 + Cl 2  CCl 4 + HCl NaCl + H 2 + O 2  NaOH + Cl 2 + H 2

Balancing Practice KClO 3  KCl + O 2 FeCl 3 + NaOH  Fe(OH) 3 + NaCl Ag 2 O  Ag + O 2 K + MgBr 2  KBr + Mg

Energy in Chemical Reactions Endothermic Reactions Endothermic Reactions More energy is absorbed to break original bonds than is released when new bonds are formed. More energy is absorbed to break original bonds than is released when new bonds are formed. Reaction feels cool. Reaction feels cool. Exothermic Reactions Exothermic Reactions More energy is released when new bonds are formed when old bonds are broken. More energy is released when new bonds are formed when old bonds are broken. Reaction feels warm. Reaction feels warm. Most reaction are exothermic reactions. Most reaction are exothermic reactions. Catalysts Catalysts Substance that lowers the activation energy of a reaction in order to speed up the reaction Substance that lowers the activation energy of a reaction in order to speed up the reaction Will NOT be used up in the process, just utilized to speed it up Will NOT be used up in the process, just utilized to speed it up