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DEFINITION OF REACTION a chemical process in which two or more substances act mutually on each other and are changed into different substances Same as saying “combine” Exp. Iron (Fe) + Oxygen (O2) = rust Physical Change Changes in physical properties melting boiling Condensation No change occurs in the identity of the substance Exp: Ice , rain, and steam are all water 3 Chemical Change Atoms in the reactants are rearranged to form one or more DIFFERENT & NEW substances Old bonds are broken new bonds form Exp: Fe and O2 form rust (Fe2O3) Ag and S form tarnish (Ag2S) LecturePLUS Timberlake 4 Indicators of chemical reactions Emission of light or heat Formation of a gas Formation of a precipitate Color change Emission of odor Learning Check E1 Classify each of the following as a 1) physical change or 2) chemical change A. ____ a burning candle B. ____ melting ice C. ____ toasting a marshmallow D. ____ cutting a pizza E. ____ polishing silver LecturePLUS Timberlake 6 Solution E1 Classify each of the following as a 1) physical change or 2) chemical change A. __2__ a burning candle B. __1_ melting ice C. __2__ toasting a marshmallow D. __1__ cutting a pizza E. __2__ polishing silver LecturePLUS Timberlake 7 Chemical Reaction A process in which at least one new substance is produced as a result of chemical change. LecturePLUS Timberlake 8 All chemical reactions: have 2 parts Reactants - the substances you start with Products- the substances you end up with The reactants turn into the products. Reactants Products A Chemical Reaction Reactants Products LecturePLUS Timberlake 10 Describing chemical reaction The way atoms are joined is changed Atoms aren’t created or destroyed. Can be described several ways: In a sentence Copper reacts with chlorine to form copper (II) chloride. In a word equation Copper + chlorine copper (II) chloride Both still mean the same thing: Cu(s) + Cl2(g) CuCl2(aq) Writing a Chemical Equation Chemical symbols give a “before-and-after” picture of a chemical reaction Reactants MgO + Products C magnesium oxide reacts with carbon CO to form LecturePLUS + Mg carbon monoxide and magnesium Timberlake 12 Matter Is Conserved H2 + Cl2 2 HCl + + Total atoms 2 H, 2 Cl = Total atoms 2H, 2 Cl Total Mass 2(1.0) + 2(35.5) 73.0 g = Total Mass 2(36.5) 73.0 g = 13 Law of Conservation of Mass In any ordinary chemical reaction, matter is not created nor destroyed LecturePLUS Timberlake 14 Symbols used in equations (s) after the formula – solid = Cu(s) (g) after the formula – gas = H2 (g) (l) after the formula - liquid = H2O(l) (aq) after the formula - dissolved in water, an aqueous solution. = CaCl2 (aq) Symbols used in equations used after a product indicates a gas (same as (g)) = O2 used after a product indicates a solid (same as (s)) = CaCo3 ---->indicates a reaction occurred or something is produced/yielded Symbols used in equations reaction. indicates a reversible shows that heat is supplied to the reaction. , or is used to indicate a catalyst used, in this case, platinum. , indicates a pressure other than STP Summary of Symbols Learning Check E3 12 oz of dough, 4 oz mushrooms, 12 slices pepperoni, 8 oz cheese and 5 oz tomato sauce are used to make a pizza. Write a recipe in words for putting together a pizza. How would you write the recipe as an equation? LecturePLUS Timberlake 19 Solution E3 Example: Combine 12 oz dough + 4 oz mushrooms + 12 slices pepperoni + 8 oz cheese + 5 oz tomato sauce and heat 30 minutes at 350°C to produce 1 pizza 12 oz dough + 4 oz mshrm + 12 pep + 8 oz chse 1 pizza + 5 oz tom sauce LecturePLUS Timberlake 20 Reading A Chemical Equation 4 NH3 + 5 O2 4 NO + 6 H2O Four molecules of NH3 react with five molecules O2 to produce four molecules NO and six molecules of H2O or Four moles NH3 react with five moles O2 to produce four moles NO and six moles H2O LecturePLUS Timberlake 21 A Balanced Chemical Equation Same numbers of each type of atom on each side of the equation Al + S Al2S3 Not Balanced 2Al + 3S Al2S3 Balanced LecturePLUS Timberlake 22 Balance Equations with Coefficients Coefficients in front of formulas balance each type of atom 4NH3 + 5O2 4NO + 6H2O 4N = 4N 12 H = 12 H 10 O = 10 O LecturePLUS Timberlake 23 Steps in Balancing An Equation (focus on one atom at a time) Fe3O4 + H2 Fe + H2O Fe: Fe3O4 + H2 3 Fe + H2O O: Fe3O4 + H2 3 Fe + 4 H2O H: Fe3O4 + 4 H2 3 Fe + 4 H2O LecturePLUS Timberlake 24 Learning Check E4 Fe3O4 + 4 H2 3 Fe + 4 H2O A. Number of H atoms in 4 H2O 1) 2 2) 4 3) 8 B. Number of O atoms in 4 H2O 1) 2 2) 4 3) 8 C. Number of Fe atoms in Fe3O4 1) 1 2) 3 LecturePLUS Timberlake 3) 4 25 Solution E4 Fe3O4 + 4 H2 3 Fe + 4 H2O A. Number of H atoms in 4 H2O 3) 8 B. Number of O atoms in 4 H2O 2) 4 C. Number of Fe atoms in Fe3O4 2) 3 LecturePLUS Timberlake 26 Learning Check E5 Balance each equation. The coefficients for each equation are read from left to right A. Mg + 1) 1, 3, 2 B. Al + 1) 3, 3, 2 N2 Mg3N2 2) 3, 1, 2 Cl2 AlCl3 2) 1, 3, 1 LecturePLUS 3) 3, 1, 1 Timberlake 3) 2, 3, 2 27 Learning Check E5 C. Fe2O3 + 1) 2, 3, 2,3 D. Al Al + + Fe 2) 2, 3, 4, 3 Fe + 2) 2, 1, 1, 1 H2SO4 1) 3, 2, 1, 2 Timberlake CO2 Al2O3 3) 3, 3, 3, 1 Al2(SO4)3 2) 2, 3, 1, 3 LecturePLUS + 3) 1, 1, 2, 3 FeO 1) 2, 3, 3, 1 E. C + H2 3) 2, 3, 2, 3 28 Solution E5 A. 3 Mg + N2 Mg3N2 B. 2 Al + 3 Cl2 2 AlCl3 C. 2 Fe2O3 + 3 C D. 2 Al + 3 FeO E. 2 Al + 3 H2SO4 LecturePLUS 4 Fe + 3 CO2 3 Fe + Al2(SO4)3 Timberlake Al2O3 + 3 H2 29 Counting with Moles Avogadro’s # - 6.02 x 1023 Because chemical reactions often involve LARGE numbers of SMALL particles, chemists use a counting unit called mole to measure amounts Exp. A mole of Iron (Fe) is 6.02 x 1023 atoms of Iron Molar Mass The mass of one mole of a substance is called the MOLAR MASS For an element, the molar mass is the same as the atomic mass expressed in grams (g) Exp. Atomic mass of carbon is 12.0 amu (found on the periodic table) so the molar mass of carbon is 12.0 grams Molar Mass in Compounds Calculate the molar mass by adding up the atomic masses of its atoms and then convert to grams Exp. Carbon dioxide CO2 – 1 atom of carbon & 2 atoms of oxygen 1 carbon atom (12.0 amu) + 2 oxygen atoms (2 x 16.0 amu = 32.0 amu) Total molar mass = 44.0 grams Mole-Mass Conversions Once you know the molar mass of a substance, you can convert moles of that substance into mass or a mass of that substance into moles Mole-Mass Example Molar mass of CO2 = 44.0 grams (12.0 + (2x16.0) = 44.0 g This means that 1 mole of CO2 = mass of 44.0 g 44.0 g CO2 / 1 mol CO2 or 1 mol CO2 / 44.0 g CO2 Suppose you have 55.0 g of CO2. Calculate how many moles of CO2 you have: 55.0 g CO2 x 1 mol CO2 / 44.0 g CO2 = 1.25 mol CO2 (Check your answer: 1.25 mol CO2 x 44.0g CO2 / 1 mol CO2 = 55.0 g CO2) Chemical Equations In chemical reactions the mass of a reactant or product can be calculated by using: Balanced chemical equation – tells you how to relate amounts of reactants to amounts of products Molar masses of the reactants and products – lets you convert amounts into masses Converting Mass to Moles Calculate how much oxygen is required to make 144 g of H2O: Determine how many moles of water you are trying to make 144 g H2O x 1 mol H2O / 18.0 g H2O = 8.00 mol H2O Copy down chart on page 197 Chemical Reactions Can be determined by: Type of reactant or # of reactants and products Types of Chemical Reactions 1. 2. 3. 4. 5. Synthesis reactions Decomposition reactions Single displacement reactions Double displacement reactions Combustion reactions 1. Synthesis Example C + O2 C + O O General: O C O A + B AB Ex. Synthesis Reaction Practice Predict the products. 2 Na(s) + Cl2(g) 2 NaCl(s) Mg(s) + F2(g) 2 Al(s) +3 F2(g) • Now, balance them. MgF2(s) 2 AlF3(s) 2. Decomposition Example: NaCl Cl Na General: Cl + Na AB A + B Ex. Decomposition Reaction 3. Single Displacement Example: Zn + CuCl2 Zn was oxidized Went from neutral (0) to (+2) Cu Cl + Cl Zn Zn Cl + Cu Cl Cu was reduced Went from (+2) to Neutral (0) General: AB + C AC + B Ex. Single Replacement Reaction Single Replacement Reactions Write and balance the following single replacement reaction equation: 2 Zn(s) + HCl(aq) ZnCl2 + H2(g) • 2 NaCl(s) + F2(g) 2NaF(s) + Cl2(g) •2 Al(s)+ 3 Cu(NO3)2(aq) 3 Cu(s)+ 2Al(NO3)3(aq) 4. Double displacement Example: MgO + CaS Mg + O General: Ca S Mg S + Ca O AB + CD AD + CB Double Replacement Reactions Think about it like “foil”ing in algebra, first and last ions go together + inside ions go together Example: AgNO3(aq) + NaCl(s) AgCl(s) + NaNO3(aq) Another example: K2SO4(aq) + Ba(NO3)2(aq) 2 KNO3(aq) + BaSO4(s) Practice Predict the products. 5. HCl(aq) + AgNO3(aq) CaCl2(aq) + Na3PO4(aq) Pb(NO3)2(aq) + BaCl2(aq) FeCl3(aq) + NaOH(aq) H2SO4(aq) + NaOH(aq) 6. KOH(aq) + CuSO4(aq) 1. 2. 3. 4. 5. Combustion Reactions Combustion reactions - a hydrocarbon reacts with oxygen gas. This is also called burning!!! In order to burn something you need the 3 things in the “fire triangle”: 1) Fuel (hydrocarbon) 2) Oxygen 3) Something to ignite the reaction (spark) Combustion Reactions In general: CxHy + O2 CO2 + H2O Products are ALWAYS carbon dioxide and water. (although incomplete burning does cause some by-products like carbon monoxide) Combustion is used to heat homes and run automobiles (octane, as in gasoline, is C8H18) Combustion Example 8 • 6 5 C5H12 + O2 CO2 + H2O Write the products and balance the following combustion reaction: • C10H22 + O2 Mixed Practice State the type & predict the products. 1. BaCl2 + H2SO4 2. C6H12 + O2 3. Zn + CuSO4 4. Cs + Br2 5. FeCO3 Synthesis Reactions Also called combination reactions 2 elements, or compounds combine to make one compound. A + B AB Na (s) + Cl2 (g) NaCl (s) Ca (s) +O2 (g) CaO (s) SO3 (s) + H2O (l) H2SO4 (s) We can predict the products if they are two elements. Mg (s) + N2 (g) Mg3N2 (s) A simulation of the reaction: 2H2 + O2 2H2O Decomposition Reactions decompose = fall apart one compound (reactant) falls apart into two or more elements or compounds. Usually requires energy A + B electricity Na + Cl2 NaCl CaCO3 CaO + CO2 AB Decomposition Reactions Can predict the products if it is a binary compound Made up of only two elements Falls apart into its elements electricity H2O H2 (g) + O2 (g) HgO Hg (s) + O2 (g) Decomposition Reactions If the compound has more than two elements you must be given one of the products The other product will be from the missing pieces NiCO3 (aq) CO2 (g) + Ni (s) H2CO3(aq) H2 (g) + CO 2 (g) Single Replacement Also referred to as single displacement One element replaces another Reactants must be an element and a compound. Products will be a different element and a different compound. A + BC AC + B 2Na + SrCl2 Sr + 2NaCl F2 + LiCl LiF + Cl2 Single Replacement We can tell whether a reaction will happen Some are more active than other More active replaces less active Double Replacement Two things replace each other. Reactants must be two ionic compounds or acids. Usually in aqueous solution AB + CD AD + CB ZnS + 2HCl AgNO3 + NaCl ZnCl + H2S AgCl + NaNO3 Combustion A reaction in which a compound (often carbon) reacts with oxygen CH4 + O2 CO2 + H2O C3H8 + O2 CO2 + H2O C6H12O6 + O2 CO2 + H2O The charcoal used in a grill is basically carbon. The carbon reacts with oxygen to yield carbon dioxide. The chemical equation for this reaction is C + O2 CO2 Acid/Base Reaction An acid and a base react to form a salt and water. Always in aqueous solution Acid (H+) + Base (OH-) → Salt + H2O NaOH + HCl → NaCl + H2O NH4OH + H2SO4 → (NH4)2SO4 + H2O How to recognize which type Look at the reactants Element(E), Compound(C) E+E C E+C C+C Acid + Base Synthesis Decomposition Single replacement Double replacement Acid/Base reaction Look at the Products CO2 + H2O Combustion Redox Examples H2 + O2 Synthesis H2O Decomposition AgNO3 + NaCl Double replacement Zn + H2SO4 Single replacement HgO Decomposition KBr +Cl2 Single replacement Mg(OH)2 + H2SO3 Double replacement Examples Acid/Base HNO3 + KOH CaPO4 Decomposition Single replacement AgBr + Cl2 Zn + O2 Synthesis HgO + Pb Single replacement HBr + NH4OH Acid/Base Cu(OH)2 + KClO3 Double replacement Summary An equation: Describes a reaction Must be BALANCED because to follow Law of Conservation of Energy Can only be balanced by changing the coefficients. Has special symbols to indicate state, and if catalyst or energy is required. Can describe 5 different types of reactions. Oxidation-Reduction Reaction A reaction in which electrons are transferred from one reactant to another. A.K.A. Redox Reaction Oxidation Any process in which an element loses electrons during a chemical reaction A reactant is oxidized if it loses electrons Exp. 2Ca + O2 2 CaO When calcium reacts with oxygen, each neutral calcium atom loses two electrons and becomes a calcium ion with a charge of +2 Reduction The process in which an element gains electrons during a chemical reaction A reactant is said to be reduced if it gains electrons Exp. O + 2e O2 Redox Reactions Compare: Contrast: Must happen together = when 1 atom loses eanother will gain it Can be a partial transfer as in the synthesis of H2O “Sharing” Oxidation – loses electrons Reduction – gains electrons Chemical Bonds and Energy Energy stored in the chemical bonds of a substance Exp. Propane – has 10 single covalent bonds; chemical energy of a propane molecule is the energy stored in these bonds Importance of Chemical Reactions Chemical reactions involve the breaking of chemical bonds in the reactants and the formation of chemical bonds in the products Energy is either released or absorbed Breaking Bonds Requires energy Exp. Why propane grills have an igniter, a device that produces a spark Spark provides enough energy to break the bonds of reacting molecules and get the reaction to start Forming Bonds Releases energy Exp. The heat and light given off by a propane stove result from the formation of new chemical bonds Exothermic and Endothermic Reactions Exothermic: Releases energy Energy released as the products form is greater than the energy required to break the bonds in the reactants Endothermic: Absorbs energy More energy is required to break the bonds in the reactants than is released by the formation of the products Reaction Energy All chemical reactions are accompanied by a change in energy. Exothermic - reactions that release energy to their surroundings (usually in the form of heat) oΔH (enthalpy) is negative – energy leaving system Endothermic - reactions that need to absorb heat from their surroundings to proceed. oΔH (enthalpy) is positive – energy coming into the system Law of Conservation of Energy Exothermic – chemical energy of the reactants is converted into heat plus the chemical energy of the products Endothermic – heat plus the chemical energy of the reactants is converted into the chemical energy of the products Both cases = total amount of energy is the same before and after the reaction Reaction Rate Rate at which reactants change into products over time Tell you how fast a reaction is going Exp. Burning calories Calories – unit of energy used in nutrition Pg. 212 in textbook Factors affecting Reaction Rates Temperature Surface area Concentration Stirring Catalysts Temperature Generally an increase in temperature will increase the reaction rate and vice versa Increasing the temperature causes the particles to move faster which are thus more likely to collide and more likely to react Surface Area Smaller the particle size of a given mass, the larger is its surface area Increase in surface area increases the exposure of reactants to one another The greater the exposure, the more collisions there are that involve reacting particles – more collisions = more reactions Stirring Stirring causes collisions between particles of the reactants Exp. Clothes in a washing machine Concentration Refers to the # of particles in a given volume The more reacting particles that are present in the given volume, the more opportunities there are for collisions involving those particles Catalysts A substance that speeds up a reaction without being used up or changed by the reaction. Often used to speed up a reaction or enable a reaction to occur at a lower temp. Lower the energy barrier (activation energy) required for a reaction to take place Reaction Energy •Spontaneous Reactions - Reactions that proceed immediately when two substances are mixed together. Not all reactions proceed spontaneously. •Activation Energy – the amount of energy that is required to start a chemical reaction. •Once activation energy is reached the reaction continues until you run out of material to react.