AP CHEMISTRY Chapter 3 © 2005 Mark S. Davis Law of Conservation of Mass • Mass is neither created nor destroyed in chemical reactions – Lavoisier © 2005 Mark S. Davis Chemical equations • Tell you: – What has – What – Ratio of – Products, reactants – Conditions © 2005 Mark S. Davis Generally • Reactants Products • Coefficients © 2005 Mark S. Davis Symbols • • • • • • (s) (l) (g) (aq) + © 2005 Mark S. Davis Example • Carbon is burned in air to form carbon dioxide • © 2005 Mark S. Davis Example • Carbon is burned in air to form carbon monoxide • 2 2 © 2005 Mark S. Davis Balancing equations • Why? – To show conservation of mass – Keep proper amounts of reactants and products – Show proper ratios between products and reactants © 2005 Mark S. Davis Example C 2H 6 + O2 CO2 + H2O © 2005 Mark S. Davis Patterns of reactivity • Groups are similar in reactivity • Alkali metals © 2005 Mark S. Davis Types of reactions • • • • • Combustion Synthesis (Combination) Decomposition Single Replacement Double Replacement © 2005 Mark S. Davis Combustion Reaction © 2005 Mark S. Davis Combustion • Occurs in air • • © 2005 Mark S. Davis Combustion Reactions • Fuel – Carbon compound • Ignition source – flame • Oxygen source © 2005 Mark S. Davis Synthesis Reaction • Reaction of two substances to form one product • Either elements or compounds react to form one compound as product • Generally: © 2005 Mark S. Davis Example Mg + O2 MgO Sodium reacts with Chlorine © 2005 Mark S. Davis Decomposition Reaction • One compound breaks apart to form two or more other elements or compounds. • Generally: • Sodium azide © 2005 Mark S. Davis Airbags © 2005 Mark S. Davis Example NaN3(s) Na(s) + N2(g) Sugar is decomposed to form carbon and water © 2005 Mark S. Davis Single Replacement • Reaction of an element and a compound to form two new substances • Generally: • Zinc and Copper sulfate © 2005 Mark S. Davis Example Zn(s) + CuSO4(aq) © 2005 Mark S. Davis Solubility Rules • In the book… table 4.1 p 111 • Also posted online. © 2005 Mark S. Davis Double Replacement • Two solutions react to form two or more new substances • Generally: • Lead (II) nitrate and potassium iodide • Identify the solid, gas, liquid, aqueous components © 2005 Mark S. Davis Example Pb(NO3)2(aq) + KI(aq) © 2005 Mark S. Davis • http://dbhs.wvusd.k12.ca.us/webdoc s/ChemTeamIndex.html • http://dbhs.wvusd.k12.ca.us/webdoc s/Equations/Equations.html © 2005 Mark S. Davis Atomic Weights • The weight of an atom of an element © 2005 Mark S. Davis Average Atomic Mass • Average mass of all the isotopes of an element – 98.5% C-12 – 1.5% C-13 © 2005 Mark S. Davis Formula Weight • The sum of the masses of all the atoms in a compound. • Usually refers to – – © 2005 Mark S. Davis Molecular Weight • The weight of all the atoms in a – – © 2005 Mark S. Davis The MOLE • Quantity of a substance © 2005 Mark S. Davis Molar Mass • The mass in grams of one mole of a substance – – © 2005 Mark S. Davis Avogadro’s Number • The number of particles in one mole of a compound • 6.022 x 1023 particles in one mole © 2005 Mark S. Davis Conversions © 2005 Mark S. Davis Empirical Formulas • Simplest formula • C6H12O6 can be reduced to • Represents the © 2005 Mark S. Davis Empirical Formulas • Ethylene glycol, the substance used in automobile antifreeze, is composed of 38.7% C, 9.7% H, and 51.6% O by mass. Its molar mass is 62.1 g/mol. What is the empirical formula? What is the molecular formula? © 2005 Mark S. Davis Empirical Formulas • Caproic acid, which is responsible for the foul odor of dirty socks, is composed of C, H, O. Combustion of 0.225 g of caproic acid produces 0.512 g CO2 and 0.209 g H2O. What is the empirical formula of caproic acid? If it has a molar mass of 116 g/mol, what is the molecular formula? © 2005 Mark S. Davis Problem • Determine the empirical formula of a compound that has the composition of 20.20 % magnesium, 26.60 % sulfur, 53.20 % oxygen. © 2005 Mark S. Davis Problem 2 • It was determined that a compound was made from 43.66 % P and 56.34 % O, what is the empirical formula? © 2005 Mark S. Davis Molecular Formulas • Represents the formula of the actual molecule • If the empirical formula is CH2O and the molar mass is 120 amu, what is the molecular formula? © 2005 Mark S. Davis Early Stoichiometry • Stoichiometry Steps for success online • Method of converting © 2005 Mark S. Davis Limiting Reactants © 2005 Mark S. Davis Theoretical Yield © 2005 Mark S. Davis