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Physical Properties color melting point boiling point electrical conductivity specific heat density state (solid, liquid, or gas) LecturePLUS Timberlake 1 Physical Change Changes in physical properties melting boiling condensation No change occurs in the identity of the substance Example: Ice , rain, and LecturePLUS steam Timberlake are all water 2 Chemical Change Atoms in the reactants are rearranged to form one or more different substances Old bonds are broken; new bonds form Examples: Fe and O2 form rust (Fe2O3) Ag and S form tarnish (Ag2S) LecturePLUS Timberlake 3 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 4 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. __1__ polishing silver LecturePLUS Timberlake 5 Chemical Reaction A process in which at least one new substance is produced as a result of chemical change. LecturePLUS Timberlake 6 - Page 321 Products Reactants A Chemical Reaction Reactants Products LecturePLUS Timberlake 8 Learning Check E2 A. How does an equation indicate a change in the identity of the reacting substances? B. How did the yellow and green reactants combine? C. Did all the reactants form product? Why or why not? LecturePLUS Timberlake 9 Learning Check E2 A. How does an equation indicate a change in the identity of the reacting substances? The formulas of the reactants are different than the formulas of the products. B. How did the yellow and green reactants combine? 1 yellow combined with 1 green. C. Did all the reactants form product? Why or why not? No. There were more yellow reactants than green. LecturePLUS Timberlake 10 All chemical reactions… • have two parts: 1. Reactants = the substances you start with 2. Products = the substances you end up with • The reactants will turn into the products. • Reactants Products In a chemical reaction • Atoms aren’t created or destroyed (according to the Law of Conservation of Mass) • A reaction can be described several ways: #1. In a sentence every item is a word Copper reacts with chlorine to form copper (II) chloride. #2. In a word equation some symbols used Copper + chlorine copper (II) chloride Symbols in equations? • the arrow (→) separates the reactants from the products (arrow points to products) –Read as: “reacts to form” or yields • The plus sign = “and” • (s) after the formula = solid: Fe(s) • (g) after the formula = gas: CO2(g) • (l) after the formula = liquid: H2O(l) Symbols used in equations • (aq) after the formula = dissolved in water, an aqueous solution: NaCl(aq) is a salt water solution Now, read these equations: Fe(s) + O2(g) Fe2O3(s) Cu(s) + AgNO3(aq) Ag(s) + Cu(NO3)2(aq) Pt NO2(g) N2(g) + O2(g) 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 16 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 17 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 5 moles O2 to produce four moles NO and six moles H2O LecturePLUS Timberlake 18 Balanced Chemical Equations • Atoms can’t be created or destroyed in an ordinary reaction: –All the atoms we start with we must end up with (meaning: balanced!) • A balanced equation has the same number of each element on both sides of the equation. 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 20 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 = LecturePLUS Timberlake 21 Law of Conservation of Mass In any ordinary chemical reaction, matter is not created nor destroyed LecturePLUS Timberlake 22 Rules for balancing: 1) Assemble the correct formulas for all the reactants and products, using “+” and “→” 2) Count the number of atoms of each type appearing on both sides 3) Balance the elements one at a time by adding coefficients (the numbers in front) where you need more - save balancing the H and O until LAST! (hint: I prefer to save O until the very last) 4) Double-Check to make sure it is balanced. • Never change a subscript to balance an equation (You can only change coefficients) – If you change the subscript (formula) you are describing a different chemical. – H2O is a different compound than H2O2 • Never put a coefficient in the middle of a formula; they must go only in the front 2NaCl is okay, but Na2Cl is not. Steps in Balancing An Equation 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 25 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 26 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 27 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 28 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 29 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 + Al2O3 Al2(SO4)3 Timberlake + 3 H2 30 Types of Reactions • There are probably millions of reactions. • We can’t remember them all, but luckily they will fall into several categories. • We will learn: a) the 4 major types. • We will be able to: b) predict the products. • For some, we will be able to: c) predict whether or not they will happen at all. • How? We recognize them by their reactants #1 –Synthesis/ Combination Reactions • Combine = put together • 2 substances combine to make one compound (also called “synthesis”) • Ca + O2 CaO • SO3 + H2O H2SO4 • We can predict the products, especially Mg3N2 (symbols, charges, cross) if the reactants are two elements. • Mg + N2 Complete and balance: Ca + Cl2 Fe + O2 (assume iron (II) oxide is the product) Al + O2 Remember that the first step is to write the correct formulas – you can still change the subscripts at this point, but not later while balancing! • Then balance by changing just the coefficients only • • • • #2 - Decomposition Reactions • decompose = fall apart • one reactant breaks apart into two or more elements or compounds. electricity • NaCl Na + Cl2 • CaCO3 CaO + CO2 • Note that energy (heat, sunlight, electricity, etc.) is usually required #2 - Decomposition Reactions • We can predict the products if it is a binary compound (which means it is made up of only two elements) –It breaks apart into the elements: electricity • H2O • HgO #3 - Single Replacement Reactions • One element replaces another • Reactants must be an element and a compound. • Products will be a different element and a different compound. • Na + KCl K + NaCl (Cations switched) • F2 + LiCl LiF + Cl2 (Anions switched) #3 Single Replacement Reactions • Metals will replace other metals (and they can also replace hydrogen) • K + AlN • Zn + HCl • Think of water as: HOH – Metals replace the first H, and then combines with the hydroxide (OH). • Na + HOH #3 Single Replacement Reactions Practice: • Fe + CuSO4 • Pb + KCl • Al + HCl #4 - Double Replacement Reactions • Two things replace each other. – Reactants must be two ionic compounds, in aqueous solution • NaOH + FeCl3 – The positive ions change place. • NaOH + FeCl3 Fe+3 OH- + Na+1 Cl-1 = NaOH + FeCl3 Fe(OH)3 + NaCl Complete and balance: • assume all of the following reactions actually take place: CaCl2 + NaOH CuCl2 + K2S KOH + Fe(NO3)3 (NH4)2SO4 + BaF2 How to recognize which type? • Look at the reactants: E + E = Combination C = Decomposition E + C = Single replacement C + C = Double replacement Practice Examples: • • • • • • • H2 + O 2 H2O Zn + H2SO4 HgO KBr + Cl2 AgNO3 + NaCl Mg(OH)2 + H2SO3 SUMMARY: An equation... • Describes a reaction • Must be balanced in order to follow the Law of Conservation of Mass • Can only be balanced by changing the coefficients. • Has special symbols to indicate the physical state, if a catalyst or energy is required, etc. LecturePLUS Timberlake 44