Intro to Chemical Reactions p74 Chapter 11 Intro1 Intro2 Warm up: Could we survive with out chemical reactions? Why or why not?

P.74 Definition: Chemical reactions alter the molecular structure of the substances involved. video Indications of a chemical change: 1. Evolution of heat and light. 2. Production of a gas. 3. Formation of a precipitate (solid). 4. Color change. 5. odor change

Chemical Equations Used to represent chemical reactions (rxn). must contain the correct formulas law of conservation of mass must be satisfied.

Chemical Equations video 2C2H2(g) + 5O2(g)  4CO2(g) + 2H2O(g) Reactants Products * is read as “yield” (also produce or form) *number in front of formula is called coefficient. (used in balancing) *(g) the state of matter

The following is a list of symbols used in chemical equations: heat Δ = reversible rxn (aq) = aqueous (s) = solid phase (l) = liquid phase (g) = gas phase or = reactants are heated = pressure at which rxn took place = temp at which rxn took place = formula of catalyst (manganese dioxide) 2 atm 0˚ MnO2

Chemical Reaction Acrostic p73 Make an acrostic on page 73 using the word: REACTION Try to use only one word and try to use the first letter for each word.

Balancing Chemical Equations p76 Warm up: What are the indications for a chemical reaction? Diatomic Molecules: 7 elements that are bound to other elements in compounds or to themselves but are never found alone. These elements are: H2, N2, O2, F2, Cl2, Br2, and I2.

“BIG 7” The 7 diatomics appear in blue

Balancing equations p76 Balancing Steps: Step 1:Write a formula equation Step 2: a. Balance the different atoms one at a time changing only the coefficients. b. Balance unique atoms first. c. Balance polyatomic ions if they appear on both sides as single units. d. Balance H atoms and O atoms last.

Balancing Chemical Equations p76 EX: Liquid water breaks down into hydrogen and oxygen gases when heated. H2O(l)  H(g) + O(g)

Avoid the following when balancing: p76 Writing incorrect chemical formulas. Balancing equations by changing the subscripts. Coefficients not in the smallest whole number ratio. EX: 4H2O(l)  4H2(g) + 2O2(g) * Factor out the LCM. video

Practice Balancing p75 Zn(s) + HCl(aq)  ZnCl2(aq) + H2(g) 2. HNO3(aq) + Mg(OH)2(s)  Mg(NO3)2(aq) + H2O(l) 2HNO3(aq) + Mg(OH)2(s)  Mg(NO3)2(aq) + 2H2O(l)

Types of Chemical Reactions p78 video Warm up: how many types of chemical rxns did you see in the video? 1. Synthesis (combination, formation) rxn 2. Decomposition rxn 3. Single replacement (displacement) rxn 4. Double replacement (displacement) rxn 5. Combustion rxn

Synthesis Rxns p78 (formation,combination) two or more substances combine to form a new compound. A + X  AX EX: 2Mg(s) + O2(g)  2MgO(s) video

Decomposition Rxns AX  A + X a single compound produces two or more simpler substances. AX  A + X EX: 2H2O(l)  2H2(g) + O2(g) video

Single Replacement Rxs one element replaces a similar element in a compound. A + BX  AX + B EX: 3Fe(s) +4H2O(l)  Fe3O4(s) + 4H2(g) video

Wow! He’s got SWAG! Stupid Jerk! Mg(s) + 2HCl(aq)  MgCl2(aq) + H2(g)

Using the Activity Series of Elements p77 Use the activity series to predict whether each of the following rxns will occur: 1. Zn(s) + H2O(l)  Will Occur 2. Cu(s) + HCl(aq)  No Reaction 3. Cd(s) + Pb(NO3)2(aq)  Will Occur 4. Al(s) + ZnCl2(aq)  Will Occur 5. Ca(s) + NaCl(s)  Will Occur 6. Co(s) + NaCl(s)  No Reaction

Double Replacement Rxns p80 Warm up: explain how one uses the activity series to predict if a reaction will occur. the ions of two compounds exchange places AX + BY  AY + BX EX: 2KI(aq) + Pb(NO3)2(aq)  PbI2(s) + 2KNO3(aq) video

Combustion Rxns CxHY + O2  CO2 + H2O a hydrocarbon combines with oxygen, releasing energy in the form of heat and light. CxHY + O2  CO2 + H2O EX: C3H8(g) + 5O2(g)  3CO2(g) + 4H2O(g) *combustion of hydrocarbons always result in the formation of CO2 and water. video

Identifying Rxns p79 Use your knowledge of rxn types to classify the following rxns: NH3(g) + HCl(g)  NH4Cl(s) C2H5OH(l) + O2(g)  CO2(g) + H2O(g) 2KClO3(s)  2KCl(s) + 3O2(g) Zn + H2SO4  ZnSO4 + H2 S(s) + O2(g)  SO2(g) AgNO3(aq) + NaCl(aq)  AgCl(s) + NaNO3(aq)

Predicting Products p79 Use your knowledge of rxn types to predict the products of the following rxns: Na + H2O  Na2O + H2 HNO3 + Ca(OH)2  Ca(NO3)2 + H2O Mg + O2  MgO

Predicting Products p79 Ca + Cl2  CaCl2 C6H14 + O2  CO2 + H2O Br2 + KI  KBr + I2 MgO + Pb  No Reaction

Predict products p79 *Now, balance these rxns to make them correct. Δ HgO  Hg + O2 Na + Cl2  NaCl NaI + Cl2  NaCl + I2 *Now, balance these rxns to make them correct.

Oxidation Reduction Reactions “Redox” LEO SAYS GER

Oxidation and Reduction (Redox) Electrons are transferred The oxidation number of atoms change

Rules for Assigning Oxidation Numbers: any uncombined element is zero 2. a monatomic ion equals its charge

Rules for Assigning Oxidation Numbers: 3. oxygen in compounds is -2 4. hydrogen in compounds is +1

Rules for Assigning Oxidation Number: 5. The sum of the oxidation numbers in a formula is 0 2(+1) + (-2) = 0 H O (+2) + 2(-2) + 2(+1) = 0 Ca O H

Rules for Assigning Oxidation Numbers: 6. The sum of the oxidation numbers of a polyatomic is equal to its charge X + 4(-2) = -2 S O X + 3(-2) = -1 N O  X = +6  X = +5

Lose Electrons = Oxidation LEO says GER : Lose Electrons = Oxidation Sodium is oxidized Gain Electrons = Reduction Chlorine is reduced

Oxidation Reduction Reactions (Redox) Each sodium atom loses one electron: Each chlorine atom gains one electron:

Reducing Agents and Oxidizing Agents The substance reduced is the oxidizing agent The substance oxidized is the reducing agent Sodium is oxidized – it is the reducing agent Chlorine is reduced – it is the oxidizing agent video

Not All Reactions are Redox Reactions Reactions in which there has been no change in oxidation number are not redox rxns. Examples:

Trends in Oxidation and Reduction Active metals: Lose electrons easily Are easily oxidized Are strong reducing agents Active nonmetals: Gain electrons easily Are easily reduced Are strong oxidizing agents