Presentation on theme: "Chemical Reactions Three areas of focus"— Presentation transcript:
1Chemical Reactions Three areas of focus Rearranging the building blocks of chemistry (atoms/ions/ molecules/electrons)Force & energy is what decides if the reaction occurs and how fastMathematics helps you keep an inventory of all the starting and ending materials
2Objectives Recognize Evidence of a chemical change. Represent chemical reactions with equations.Change word equations into formula equations.Given a description of a reaction, write a word and formula equation.Balance chemical equations.Translate a formula equation into a sentence.Define and give a description of the major types of chemical reactions.Classify reactions as one of five major types.Predict the products of simple reactions when given the reactants.Understand, explain, and apply the activity series of the elements.
3Skills Memorize the diatomic elements Memorize the diatomic elementsMemorize the symbols used in chemical equations.Use the Activity Series for single replacement reactionsUse the Solubility Chart for Double Replacement ReactionsKnow common gasesMemorize substances that decomposeCarbonic acid, H2CO H2CO3 (aq) H2O+ CO2(g) Sulfurous acid, H2SO H2SO3(aq) H2O + SO2(g)Ammonium hydroxide, NH4OH NH4OH (aq H2O + NH3(g)
4We are making something new! Chemical ReactionThe process by which one or more substances are rearranged to form different substances is called a chemical reaction.Also called a chemical changeWe are making something new!
5Equations show the reactants which enter into a reaction. the products which are formed by the reaction.the relative amounts of each substance used and each substance produced.
6Two important principles to remember Every chemical compound has a formula which cannot be altered.A chemical reaction must account for every atom that is used. This is an application of the Law of Conservation of Matter which states that in a chemical reaction atoms are neither created nor destroyed.
11Some things to remember about writing equations The diatomic elements are always written H2, N2, O2, F2, Cl2, Br2, I2The sign, → , means "yields" and shows the direction of the action.A small delta, ( ), above the arrow shows that heat has been added.A double arrow, ↔ , shows that the reaction is reversible and can go in both directions.
12Word EquationsUsing words in equation form to represent a chemical reactioniron(s) + chlorine(g) iron(III) chloride(s)
13Practice Skeleton Equation uses chemical formulas instead of words Fe (s) + Cl2 (g) ----- FeCl3 (s)Practice
14Chemical EquationIn order to obey the Law of Conservation of Mass equations must be Balanced:Coefficients: number written in front of a chemical formula to indicate the smallest number of particles involved in the reaction.
15Steps for Balancing Write skeleton equation. Change the coefficients to make the number of atoms of each element equal on both sides of the equation. NEVER CHANGE A SUBSCRIPT!!!Write the coefficients in the smallest ratio possible.Check your work.
16Helpful hints for balancing chemical equations Start with “Big Formulas” C2H6O2Save single elements for last O2 or CuBalance hydrogens second to lastBalance oxygens lastCheck for lowest ratioDo not change your subscriptsBalance the polyatomic ions as one unit (if it didn’t break apart)Perform a final check
17If your equation doesn’t balance, check your formulas!!
20Classifying Chemical Reactions Five Types of Chemical ReactionsSynthesis ReactionDecomposition ReactionSingle Replacement ReactionDouble replacement ReactionCombustion Reaction: oxygen combines with a substance and produces heat and light
21Synthesis Reaction: one product is formed from more than one simpler substances A + B AB
22Decomposition Reaction: One substance is broken down into one or more simpler substances: usually by the addition of energyAB A + B
23Single Replacement Reaction: atoms of one element replace another element in a compound A + BC B + AC
24Double replacement Reaction: involves the exchange of ions between two compounds AB + CD AD + CB
25Combustion Reaction: oxygen combines with a substance and produces heat and light X + O2 H2O + CO2
34How can we tell if a single replacement reaction will happen? Use the activity series of the elementsIf the free element is more active than the element in the compound the reaction will happenIf the free element is below the element in the compound the reaction will not happen
39Double Replacement Reactions two ionic compounds are mixed together in waterIn water the ionic compounds split into anions and cations.The cations have an opportunity to swap anionsA reaction occurs, if by swapping anions, a product is formed that cannot split apart into anions and cationsAB + CD AD + CB
42Double Replacement: Will it occur? A reaction occurs when a pair of ions comes together to produce a substance that removes ions from the solution.one of the following must occura precipitate: a solid produced during a reactiona gasWater or other unionized substancea product that decomposes
43NaNO3(aq) + KCl(aq)� � NaCl(aq) + KNO3(aq) No Driving ForceWhat happens when one of the three possible products is not formed?NothingAll ions remain in solution (dissolved)NaNO3(aq) + KCl(aq)� � NaCl(aq) + KNO3(aq)
44Without a driving force there is no change in the solution so we say No Reaction has taken place
45Reactions that form a Precipitate PbCl2(aq) + KI(aq) PbI2(s)+ KCl(aq) Solubility Chart
47Reactions that form a Gas Some double replacement reactions produce a gas. We observe this as bubbles or odors given off. Example:Na2S (aq) + H2SO4 (aq) Na2SO4 (aq) + H2S(g)
48Products that Decompose Some metathesis reactions do not give the product expected.the expected product (H2CO3) decomposes to give a gaseous product (CO2)CaCO3 (s) + HCl (aq) CaCl2 (aq) + H2CO3CaCO3 (s) + HCl (aq) CaCl2 (aq) + CO2 (g) + H2O (l)Products that DecomposeH2SO3 H2O + SO2H2CO3 H2O + CO2NH4OH H2O + NH3
49Reactions that form Water These water molecules increase the number of solvent molecules and we see no observable evidenceUsually accompanied by temperature change orNeutralization which can be seen with an acid base indicatorExample: H2SO4 + NaOH Na2SO4 + H2O
50Neutralization Reactions Generally, when solutions of an acid and a base are combined, the products are a salt and waterHC2H3O2 (aq) + NaOH (aq) NaC2H3O2 (aq) + H2O (l)Acid + Base Salt + Water
51Molecular EquationThe molecular equation lists the reactants and products in their molecular form.AgNO3 (aq) + KCl (aq) AgCl (s) + KNO3 (aq)
52Ionic EquationIn the ionic equation all strong electrolytes (strong acids, strong bases, and soluble ionic salts) are dissociated into their ions.This more accurately reflects the species that are found in the reaction mixture.Ag+ (aq) + NO3- (aq) + K+ (aq) + Cl- (aq)
53Net Ionic EquationTo form the net ionic equation, cross out anything that does not change from the left side of the equation to the right.Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq) AgCl (s) + K+(aq) + NO3-(aq)
54Net Ionic EquationThe only things left in the equation are those things that change (i.e., react) during the course of the reaction.Ag+(aq) + Cl-(aq) AgCl (s)
55Those things that didn’t change (and were deleted from the net ionic equation) are called spectator ions.Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq) AgCl (s) + K+(aq) + NO3-(aq)
56Writing Net Ionic Equations Write a balanced molecular equation.Dissociate all strong electrolytes (strong acids, strong bases, and soluble ionic salts)Cross out anything that remains unchanged from the left side to the right side of the equation.Write the net ionic equation with the species that remain.
59Combustion of Hydrocarbons Hydrocarbon + oxygen CO2 + H2OHydrocarbon: A compound of hydrogen and carbonThe phrase "To burn" means to add oxygen unless told otherwise.
60Incomplete Combustion: Hydrocarbon + oxygen CO2 + H2OComplete combustion means the higher oxidation number is attained.Incomplete Combustion:Hydrocarbon + oxygen CO + H2OIncomplete combustion means the lower oxidation number is attained.
61Combustion of Hydrocarbons If oxygen is sufficient, the products are carbon dioxide and water vapor.If oxygen is low, carbon monoxide will be produced.automobile engine inside a closed garage or charcoal grill indoors.
76Examples of Decomposition Reactions AX → A + X Metallic carbonates, when heated, form metallic oxides and CO2(g)CaCO3(s) → CaO(s) + CO2(g)Most metallic hydroxides, when heated, decompose into metallic oxides and waterCa(OH)2(s) → CaO(s) + H2O(g)Metallic chlorates, when heated, decompose into metallic chlorides and oxygen2KClO3(s) → 2KCl(s) + 3O2(g)Some acids, when heated, decompose into nonmetallic oxides and waterH2SO4 → H2O(l) + SO3(g)Some oxides, when heated, decompose2HgO(s) → 2Hg(l) + O2(g)Some decomposition reactions are produced by electricity2H2O(l) → 2H2(g) + O2(g)2NaCl(l) → 2Na(s) + Cl2(g)
77SummaryA + B AB (synthesis) AB A + B (decomposition) A + BC B + AC (single replacement) AB + CD AC + BD (double replacement) Hydrocarbon + oxygen CO2 + H2O (combustion/oxidation)