Chapter 11 Chemical Reactions

Chemical Equation Describes chemical reaction. Chemical equation: reactants yield products Reactants  Products Much easier to write symbols and formulas instead of words

Examples CH4(g) + O2(g)  CO2(↑) + H2O(↑) Solid Iron reacts with oxygen gas to form the solid IronIIIoxide. iron(s) + oxygen(g)  ironIIIoxide(s) Fe(s) + O2(g)  Fe2O3(s) Carbon tetrahydride gas BURNS to form carbon dioxide gas and water vapor. Carbon tetrahydride(g) + oxygen(g)  carbon dioxide(↑) + water(↑) CH4(g) + O2(g)  CO2(↑) + H2O(↑) Skeleton Equation: chemical equation that tells you what the reactants and products are but NOT how much of each you have. First step in writing a chemical equation.

Symbols Used (s) solid (l) liquid (g) gas (↑) gas as a product (aq) aqueous (in water solution) () ppt (precipitate) solid product from 2 aqueous reactants D means with heat Pt means with Platinum catalyst: speeds up a reaction without being used.  reversible reaction

Balancing Chemical Equations Balanced equations have: the same # of atoms of each element on BOTH sides of the equation. Law of Conservation of Mass – atoms can neither be created nor destroyed, simply rearranged.

Rules for Balancing Equations Get the correct formulas for reactants and products. (USE ION CHART AND DON”T FORGET DIATOMIC ELEMENTS!) Write reactants on left, products on right. Use plus signs to separate compounds and yield sign to separate the reactants from products.

Rules Continued Count the # of atoms of each element in reactants and products. (Polyatomic atoms on both sides count as one.) Balance # of each element using coefficients. Coefficient – small whole # in front of a formula. NEVER CHANGE FORMULA SUBSCRIPTS

Rules for Balancing Equations Balance elements appearing 3 or more places LAST. Check each element to make sure equation is balanced. Make sure all coefficients are in the lowest whole number ratio. Do not change subscripts!!!

H O N Cl Br I F Diatomic Molecules There are 7 naturally occurring Diatomic Molecules- a molecule made up two atoms of the same element. They are only diatomic when they are alone. There are 7 naturally occurring diatomic molecules. H O N Cl Br I F

Balancing Examples ___ C(s) + ___ O2(g)  ___ CO2 (g) ___ AgNO3(aq) + ___Cu(s)  ___ Cu(NO3)2(aq) + ___ Ag(s) ___ Al(s) + ___ O3(g)  ___ Al2O3(s) *___ C2H6(g) + ___ O2(g)  ___ CO2(g) + ___ H2O(g) *___ H3PO3  ___ H3PO4 + PH3

5 Types of Chemical Reactions Combination Reaction – elements combine to form a compound. A + B AB element + element  compound Ex. Sodium + chlorine  sodium chloride ___Na(s) + ___ Cl2(g)  ___ NaCl(s) 2 2

5 Types of Reactions AB  A + B compound  element + element Decomposition Reaction – compound breaks down into its element. AB  A + B compound  element + element Ex: MercuryII oxide  mercury + oxygen ___ HgO  ___Hg + ___O2 2 2

AB + C A + CB or AB + D AD + B 5 Types of Reactions - 3 Single Replacement Reaction – one element replaces another element in a compound. AB + C A + CB or AB + D AD + B + - + + + - + - - + - -

Examples of Single Replacement Reactions Must use Activity Series to see if reaction works Zinc + sulfuric acid  zinc sulfate + hydorgen Zn(s) + H2SO4(aq)  ZnSO4(aq) + H2(↑) Periodic table is activity series for halogens Sodium bromide + chlorine  sodium chloride + bromine ___NaBr(s) + ___Cl2(g)  ___NaCl(s) + ___Br2(↑) 2 2

AB + CD AD + CB 5 Types of Reactions Double Replacement Reaction – two compounds react and exchange positive ions to form two new compounds. AB + CD AD + CB Barium Chloride(aq) + potassium carbonate(aq)  barium carbonate() + potassium chloride(aq) BaCl2(aq) + K2CO3(aq)  BaCO3() + ___ KCl(aq) + - + - + - + - 2

CxHy + O2 CO2 + H20 5 Types of Reactions Combustion Reaction – oxygen reacts with a compound composed of C and H. CxHy + O2 CO2 + H20 Also called Burning (exothermic) The products are always CO2 and H2O.

Examples of Combustion Reactions 1. C6H6 + O2 CO2 + H2O 7½ 6 3 2 15 12 6 C6H6 + O2 CO2 + H2O 2. CH3OH + O2 CO2 + H2O 1½ 2 2 3 2 4 CH3OH + O2 CO2 + H2O

Special Decomposition Reactions: Decomposition of a Carbonate: Metal carbonate  metal oxide + carbon dioxide XCO3 XO + CO2 ex. Na2CO3 Na2O + CO2

Special Decomposition Reactions: Decomposition of a Hydroxide: Metal hydroxide  metal oxide + water XOH XO + H2O ex. 2NaOH Na2O + H2O

Special Decomposition Reactions: Decomposition of a Chlorate: (ClO3) Metal chlorate  metal chloride + oxygen XClO3 XCl + O2 ex. ___NaClO3 ___NaCl + ___O2 2 3

Special Decomposition Reactions: 4 Special single Replacement Reaction: Group IA or IIA metal and H2O X + HOH XOH + H2 ex. 2Na + 2HOH 2NaOH + H2

How to ID types of reactions. Combination Reactions – given 2 items that form 1 new compound. Decomposition Reactions – given a single compound that breaks into parts. Single Replacement – given a single element plus a single compound, forms a new compound a a different element. Double Replacement – given two compounds (+’s change places). Combustion Reaction – given CH compound with Oxygen, always forms water and carbon dioxide.

The End