Ch. 8 Notes -- Chemical Reactions Chemical equations give information in two major areas: 1. _____________ and ______________ of the reaction. 2. Coefficients of a balanced chemical equation tell us the ______ of the substances involved. Example of a Balanced Chemical Equation: 2H2 (g) + O2 (g)  2H2O (g) Reactants are on the ______ side of the arrow, and the products are on the __________ side. The arrow means “________”, or “reacts to produce” when read aloud. From our example, hydrogen reacts with oxygen in a ___:___ ratio. The coefficients represent either the number of _________ or molecules present. Reactants products amount left right yields 2 1 moles

Common Symbols used in Chemical Equations + = used to separate 2 reactants or 2 products from each other → = “yields” or “reacts to produce” = _____________ reaction (like a rechargeable battery) (s) (l) (g) (aq) = phase of matter: (solid, liquid, gas, or “aqueous”) = ___________ supplied to the reaction MnO2 = a catalyst, (in this case, MnO2), is used to ________ ____ the reaction. reversible heat speed up

Common Acids used in Chemical Equations The formula for acids start with a ________________________. We will learn more about the properties of acids and bases next semester. Here is a list of common acids: HCl ______________________ HNO3 ______________________ H2SO4 ______________________ HC2H3O2 ______________________ Hydrogen Hydrochloric Acid Nitric Acid Sulfuric Acid Acetic Acid

Decoding Common Chemical Equation Symbols Practice Problems: Describe the following reactions using complete sentences. a) NaHCO3 (s) + HCl (aq)  NaCl (aq) + H2O (l) + CO2 (g) b) H2SO4 (aq) + BaCl2 (aq)  HCl (aq) + BaSO4 (s) c) Write a chemical equation from the following description: “Sodium plus bromine, when heated, reacts to produce solid sodium bromide.” Solid sodium bicarbonate plus aqueous hydrochloric acid yields aqueous sodium chloride plus liquid water plus carbon dioxide gas. Aqueous sulfuric acid plus aqueous barium chloride yields aqueous hydrochloric acid plus solid barium sulfate. Na (s) + Br2  NaBr (s) (l)

Balancing Chemical Equations Why do you have to balance a chemical equation? Law of Conservation of Matter (or Mass): “Matter is neither ____________ nor _______________ in chemical reactions.” During a chemical reaction, atoms are either _________, ______________, or rearranged. The _____________ and type of each atom stays the same. How do you balance a chemical equation? __________________ are placed in front of the substances involved in the chemical reaction to get the same number of atoms of each element on both sides of the equation. This number will multiply the number of atoms there are in a formula. created destroyed joined separated number Coefficients

Rules for Balancing Chemical Equations (1) Coefficients can only be placed ___ _________ of a chemical formula. Practice Problems: How many atoms of each type are indicated in the following compounds? (a) 2 (NH4)3PO4 N= ___ H= ___ P= ___ O= ___ (b) 4 KC2H3O2 K= ___ C= ___ H= ___ O= ___ (c) 3 Ca(NO3)2 Ca= ___ N= ___ O= ___ in front 6 24 2 8 4 8 12 8 3 6 18

Rules for Balancing Chemical Equations (2) You cannot change a ________________!! Example : H2 + O2  H2O To balance oxygen, you cannot change water’s formula to_________! (3) You cannot place the coefficient in the ______________ of a formula!! Example : Al + N2  AlN To balance nitrogen, you cannot put a 2 in the middle to make _______. (4) Reduce the coefficients to the simplest ____________ ___ ratio. Example: 4H2 + 2O2  4H2O can be reduced to… __H2 + __O2  __H2O subscript 2 2 H2O2 middle 2 2 Al2N whole # 2 1 2

Rules for Balancing Chemical Equations (5) Get rid of any ____________! Coefficients must be _________ #’s You can’t have a _______________ of a molecule or atom! Example: 1H2 + ½O2  1H2O changes to… __ H2 + __O2  __H2O fractions whole fraction 2 x ( ) 2 1 2

Balancing Equations: “Helpful Hints” a) Balance elements that appear in more than one compound ________. ___(NH4)2CO3  ___NH3 + ___CO2 + ___H2O b) Balance _____ “___________” as though it were one item as long as the ion stays together as a group on each side of the yields arrow. ___Al + ___CuSO4  ___Al2(SO4)3 + ___Cu c) If you can’t seem to get it balanced, _________ _________ and begin with a different element the next time, or put a “2” somewhere and then try again. ___Li + ___H2O  ___LiOH + ___H2 This is what I’ll constantly be telling you to do if you are stuck and you need my help... “Pick an element to balance. How many are on the left side? How many are on the right side? ________ ____!” ___Fe(OH)3  ___Fe2O3 + ___H2O last 1 2 1 1 ion chunks 2 3 1 3 start over 2 2 2 1 Fix it 2 1 3

Balancing Equations: “Helpful Hints” e) Mr. Reid’s goofy “balancing song” may help: “If there’s a ___ on the left and a ___on the right, you put a ___ on the left and a ___ on the right, (makin’ money!)” ___Al + ___O2  ___Al2O3 f) If you see only C’s H’s and O’s, balance them in this order: C, H, O. ___C2H2 + ___O2  ___CO2 + ___H2O 2 3 3 2 4 3 2 2 5 4 2