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Chemical Reactions Three areas of focus

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1 Chemical 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 fast Mathematics helps you keep an inventory of all the starting and ending materials

2 Objectives 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.

3 Skills Memorize the diatomic elements
Memorize the diatomic elements Memorize the symbols used in chemical equations. Use the Activity Series for single replacement reactions Use the Solubility Chart for Double Replacement Reactions Know common gases Memorize substances that decompose Carbonic acid, H2CO H2CO3 (aq) H2O+ CO2(g)  Sulfurous acid, H2SO H2SO3(aq)  H2O + SO2(g) Ammonium hydroxide, NH4OH NH4OH (aq H2O + NH3(g)

4 We are making something new!
Chemical Reaction The process by which one or more substances are rearranged to form different substances is called a chemical reaction. Also called a chemical change We are making something new!

5 Equations 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.

6 Two 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.

7 Evidence of a Chemical Reaction

8 Evidence of a Chemical Reaction
Production of a Gas Temperature Change Color Change Production of a Solid (precipitate) Production of Water or other unionized substance

9 Representing Reactions
chemical equations – represent reactions Reactants - starting Substances Products – ending substance Symbols??


11 Some things to remember about writing equations
The diatomic elements are always written H2, N2, O2, F2, Cl2, Br2, I2 The 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.

12 Word Equations Using words in equation form to represent a chemical reaction iron(s) + chlorine(g) iron(III) chloride(s)

13 Practice Skeleton Equation uses chemical formulas instead of words
Fe (s) + Cl2 (g) ----- FeCl3 (s) Practice

14 Chemical Equation In 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.

15 Steps 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.

16 Helpful hints for balancing chemical equations
Start with “Big Formulas” C2H6O2 Save single elements for last O2 or Cu Balance hydrogens second to last Balance oxygens last Check for lowest ratio Do not change your subscripts Balance the polyatomic ions as one unit (if it didn’t break apart) Perform a final check

17 If your equation doesn’t balance, check your formulas!!



20 Classifying Chemical Reactions
Five Types of Chemical Reactions Synthesis Reaction Decomposition Reaction Single Replacement Reaction Double replacement Reaction Combustion Reaction: oxygen combines with a substance and produces heat and light

21 Synthesis Reaction: one product is formed from more than one simpler substances
A + B  AB

22 Decomposition Reaction: One substance is broken down into one or more simpler substances: usually by the addition of energy AB  A + B

23 Single Replacement Reaction: atoms of one element replace another element in a compound
A + BC  B + AC

24 Double replacement Reaction: involves the exchange of ions between two compounds
AB + CD  AD + CB

25 Combustion Reaction: oxygen combines with a substance and produces heat and light
X + O2  H2O + CO2

26 Classify Each Reaction
Ca + O2  CaO Br + LiI  LiBr + I Al + Fe(NO3)2  Al(NO3)3 + Fe MgO + HCl  MgCl2 + H2O C4H O2  CO2 + H2O NH4NO2  NH3 + H2O (NH4)3PO4 + Sr(OH)2  Sr3(PO4)2 + NH4OH H2SO4 + NaOH  Na2SO4 + H2O Zn + AgNO3  Zn(NO3)2 + Ag CuNO3 + KCl  KNO3 + CuCl


28 Predicting Products Given the reactants predict what is formed
Write formulas for reactants Identify the type of reaction Rearrange the atoms to write formulas for products.

29 Single Replacement Reactions
Atoms of one element replace another element in a compound A + BC  B + AC There are 3 Ways that a Single Replacement Reaction can occur.

30 1.) Metal replaces another metal in a compound
when zinc combines with iron (II) chloride the zinc replaces iron in the compound Z n + FeCl2  Fe + ZnCl2

31 2.) Metal replaces hydrogen in an acid or water

32 3.) Nonmetal (halogen) replaces another nonmetal (halogen)in a compound
Br2 + LiI  LiBr + I2

33 Single Replacement Cartoon

34 How can we tell if a single replacement reaction will happen?
Use the activity series of the elements If the free element is more active than the element in the compound the reaction will happen If the free element is below the element in the compound the reaction will not happen

35 The Activity Series

36 Another way to look at it
Bigger, stronger, orange shirted guy replaces white shirt guy in the dancing couple Now we have new couple and new single guy

37 Single Replacement Lab and Examples for you to Predict the Products
Some Examples to Observe before lab


39 Double Replacement Reactions
two ionic compounds are mixed together in water In water the ionic compounds split into anions and cations. The cations have an opportunity to swap anions A reaction occurs, if by swapping anions, a product is formed that cannot split apart into anions and cations AB + CD  AD + CB

40 AgNO3(aq) + KCl(aq)  AgCl(s) + KNO3(aq)


42 Double 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 occur a precipitate: a solid produced during a reaction a gas Water or other unionized substance a product that decomposes

43 NaNO3(aq) + KCl(aq)� � NaCl(aq) + KNO3(aq)
No Driving Force What happens when one of the three possible products is not formed? Nothing All ions remain in solution (dissolved) NaNO3(aq) + KCl(aq)� � NaCl(aq) + KNO3(aq)

44 Without a driving force there is no change in the solution so we say No Reaction has taken place

45 Reactions that form a Precipitate PbCl2(aq) + KI(aq)  PbI2(s)+ KCl(aq) Solubility Chart


47 Reactions 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)

48 Products 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) + H2CO3 CaCO3 (s) + HCl (aq)  CaCl2 (aq) + CO2 (g) + H2O (l) Products that Decompose H2SO3  H2O + SO2 H2CO3  H2O + CO2 NH4OH  H2O + NH3

49 Reactions that form Water
These water molecules increase the number of solvent molecules and we see no observable evidence Usually accompanied by temperature change or Neutralization which can be seen with an acid base indicator Example: H2SO4 + NaOH  Na2SO4 + H2O

50 Neutralization Reactions
Generally, when solutions of an acid and a base are combined, the products are a salt and water HC2H3O2 (aq) + NaOH (aq) NaC2H3O2 (aq) + H2O (l) Acid + Base  Salt + Water

51 Molecular Equation The molecular equation lists the reactants and products in their molecular form. AgNO3 (aq) + KCl (aq)  AgCl (s) + KNO3 (aq)

52 Ionic Equation In 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)

53 Net Ionic Equation To 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)

54 Net Ionic Equation The 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)

55 Those 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)

56 Writing 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.



59 Combustion of Hydrocarbons
Hydrocarbon + oxygen  CO2 + H2O Hydrocarbon: A compound of hydrogen and carbon The phrase "To burn" means to add oxygen unless told otherwise.

60 Incomplete Combustion:
Hydrocarbon + oxygen  CO2 + H2O Complete combustion means the higher oxidation number is attained. Incomplete Combustion: Hydrocarbon + oxygen  CO + H2O Incomplete combustion means the lower oxidation number is attained.

61 Combustion 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.

62 Hydrocarbon (CxHy) + O2(g) → CO2(g) + H2O(g)
EX. CH4(g)  +  2O2(g)  →    CO2(g)  +  2H2O(g) EX. 2C4H10(g)  +  13O2(g)  →    8CO2(g)  +  10H2O(g)

63 Combustion of Propane C3H8 + O2 --> CO2 + H2O
propane 3 carbons = 3 carbon dioxide molecules 8 hydrogen atoms = four H2O molecules. balance the oxygen

64 Combustion of Acetylene
This combustion of acetylene reaction is exothermic, and enough energy is released to melt metal. Used in welding. Why So Hot??

65 Triple bond -multiple bonds -short bond length

66 Combustion Of Methane Demo: Methane Snake Reaction



69 Synthesis Reactions A + B  AB Elem/Cmpd + Elem/Cmpd  Compound
One Product



72 Examples of Synthesis Reactions
Metal  +  oxygen  →   metal oxide 2Mg(s)  +  O2(g)  →    2MgO(s) Nonmetal  +  oxygen  →    nonmetallic oxide C(s)  +  O2(g)  →    CO2(g) Metal oxide  +  water  →    metallic hydroxide MgO(s)  +   H2O(l)  →    Mg(OH)2(s) Nonmetallic oxide  +  water  →    acid CO2(g)  +  H2O(l)  →    ; H2CO3(aq) Metal + nonmetal  →    salt 2 Na(s)  +  Cl2(g)  →    2NaCl(s) A few nonmetals combine with each other 2P(s)  +  3Cl2(g)  →    2PCl3(g) These two reactions must be remembered: N2(g)  +  3H2(g)  →    2NH3(g) NH3(g)  +  H2O(l)  →    NH4OH(aq)

73 Decomposition Reactions
AB  A + B Compound Cmpd/Elem + Elem/Cmpd One Reactant



76 Examples 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 water Ca(OH)2(s)  →    CaO(s)  +  H2O(g) Metallic chlorates, when heated, decompose into metallic chlorides and oxygen 2KClO3(s)  →    2KCl(s)  +  3O2(g) Some acids, when heated, decompose into nonmetallic oxides and water H2SO4  →    H2O(l)  +  SO3(g) Some oxides, when heated, decompose 2HgO(s)  →    2Hg(l)  +  O2(g) Some decomposition reactions are produced by electricity 2H2O(l)  →    2H2(g)  +  O2(g) 2NaCl(l)  →    2Na(s)  +  Cl2(g)

77 Summary A + 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)


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