LecturePLUS Timberlake1 Physical Properties color melting point boiling point electrical conductivity specific heat density state (solid, liquid, or gas)

LecturePLUS Timberlake2 Physical Change Changes in physical properties melting boiling condensation No change occurs in the identity of the substance Example: Ice, rain, and steam are all water

LecturePLUS Timberlake3 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 O 2 form rust (Fe 2 O 3 ) Ag and S form tarnish (Ag 2 S)

LecturePLUS Timberlake4 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 Timberlake5 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 Timberlake6 Chemical Reaction A process in which at least one new substance is produced as a result of chemical change.

- Page 321 Reactants Products

LecturePLUS Timberlake8 A Chemical Reaction Reactants Products

LecturePLUS Timberlake9 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 Timberlake10 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.

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: CO 2(g) (l) after the formula = liquid: H 2 O (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) + O 2(g)  Fe 2 O 3(s) Cu (s) + AgNO 3(aq)  Ag (s) + Cu(NO 3 ) 2(aq) NO 2(g) N 2(g) + O 2(g)

LecturePLUS Timberlake16 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 Timberlake17 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 Timberlake18 Reading A Chemical Equation 4 NH O 2 4 NO + 6 H 2 O Four molecules of NH 3 react with five molecules O 2 to produce four molecules NO and six molecules of H 2 O or Four moles NH 3 react with 5 moles O 2 to produce four moles NO and six moles H 2 O

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.

LecturePLUS Timberlake20 A Balanced Chemical Equation Same numbers of each type of atom on each side of the equation Al + S Al 2 S 3 Not Balanced 2Al + 3S Al 2 S 3 Balanced

LecturePLUS Timberlake21 Matter Is Conserved H 2 + Cl 2 2 HCl ++ Total atoms=Total atoms 2 H, 2 Cl2H, 2 Cl Total Mass=Total Mass 2(1.0) + 2(35.5)2(36.5) 73.0 g=73.0 g

LecturePLUS Timberlake22 Law of Conservation of Mass In any ordinary chemical reaction, matter is not created nor destroyed

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. –H 2 O is a different compound than H 2 O 2 Never put a coefficient in the middle of a formula; they must go only in the front 2 NaCl is okay, but Na 2 Cl is not.

LecturePLUS Timberlake25 Steps in Balancing An Equation Fe 3 O 4 + H 2 Fe + H 2 O Fe: Fe 3 O 4 + H 2 3 Fe + H 2 O O:Fe 3 O 4 + H 2 3 Fe + 4 H 2 O H: Fe 3 O H 2 3 Fe + 4 H 2 O

LecturePLUS Timberlake26 Learning Check E4 Fe 3 O H 2 3 Fe + 4 H 2 O A. Number of H atoms in 4 H 2 O 1) 22) 43) 8 B. Number of O atoms in 4 H 2 O 1) 22) 43) 8 C. Number of Fe atoms in Fe 3 O 4 1) 12) 33) 4

LecturePLUS Timberlake27 Solution E4 Fe 3 O H 2 3 Fe + 4 H 2 O A. Number of H atoms in 4 H 2 O 3) 8 B. Number of O atoms in 4 H 2 O 2) 4 C. Number of Fe atoms in Fe 3 O 4 2) 3

LecturePLUS Timberlake28 Learning Check E5 Balance each equation. The coefficients for each equation are read from left to right A. Mg + N 2 Mg 3 N 2 1) 1, 3, 2 2) 3, 1, 2 3) 3, 1, 1 B. Al + Cl 2 AlCl 3 1) 3, 3, 22) 1, 3, 13) 2, 3, 2

LecturePLUS Timberlake29 Learning Check E5 C. Fe 2 O 3 + C Fe + CO 2 1) 2, 3, 2,3 2) 2, 3, 4, 3 3) 1, 1, 2, 3 D. Al + FeO Fe + Al 2 O 3 1) 2, 3, 3, 1 2) 2, 1, 1, 1 3) 3, 3, 3, 1 E. Al + H 2 SO 4 Al 2 (SO 4 ) 3 + H 2 1) 3, 2, 1, 2 2) 2, 3, 1, 3 3) 2, 3, 2, 3

LecturePLUS Timberlake30 Solution E5 A. 3 Mg +N 2 Mg 3 N 2 B. 2 Al + 3 Cl 2 2 AlCl 3 C. 2 Fe 2 O C 4 Fe + 3 CO 2 D. 2 Al + 3 FeO 3 Fe + Al 2 O 3 E. 2 Al + 3 H 2 SO 4 Al 2 (SO 4 ) H 2

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 + O 2  CaO SO 3 + H 2 O  H 2 SO 4 We can predict the products, especially if the reactants are two elements. Mg + N 2  Mg 3 N 2 (symbols, charges, cross)

Complete and balance: Ca + Cl 2  Fe + O 2  (assume iron (II) oxide is the product) Al + O 2  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. NaCl Na + Cl 2 CaCO 3 CaO + CO 2 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: H 2 O 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 F 2 + LiCl  LiF + Cl 2 (Cations switched) (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 + CuSO 4  Pb + KCl  Al + HCl 

#4 - Double Replacement Reactions Two things replace each other. –Reactants must be two ionic compounds, in aqueous solution NaOH + FeCl 3  –The positive ions change place. NaOH + FeCl 3  Fe +3 OH - + Na +1 Cl -1 = NaOH + FeCl 3  Fe(OH) 3 + NaCl

Complete and balance: assume all of the following reactions actually take place: CaCl 2 + NaOH  CuCl 2 + K 2 S  KOH + Fe(NO 3 ) 3  (NH 4 ) 2 SO 4 + BaF 2 

How to recognize which type? Look at the reactants: E + E =Combination C =Decomposition E + C =Single replacement C + C =Double replacement

Practice Examples: H 2 + O 2  H 2 O  Zn + H 2 SO 4  HgO  KBr + Cl 2  AgNO 3 + NaCl  Mg(OH) 2 + H 2 SO 3 

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.

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