GENERAL CHEMISTRY 1 NOTES BY Part 1 TABLE OF CONTENTS 01 MATTER AND MEASUREMENT 02 ATOMS, MOLECULES, IONS 03 CHEMICAL REACTIONS & STOICHIOMETRY 04 AQUEOUS REACTIONS & SOLUTION STOICHIOMETRY 05 THERMOCHEMISTRY 1. 01 : MATTER AND MEASUREMENT SI BASE UNITS Chemistry is the study of matter and the changes it undergoes. Matter is anything that occupies space and has mass. The three states of matter are solid, liquid, gas. CLASSIFICATION OF MATTER METRIC SYSTEM PREFIXES VOLUME AND TEMPERATURE CONVERSIONS Mixtures can be separated based on physical properties of the components of the mixture. Some methods used are filtration, distillation, and chromatography. Chemical Properties can only be observed when a substance is changed into another substance. (ex. flammability, corrosiveness, or reactivity) 0F = 1.8 x 0C + 32 Density – a fundamental property of all substance & differs from one substance to another. mass 3 3 1 g/cm = 1 g/mL = 1000 kg/m density = volume RULES FOR SIGNIFICANT FIGURES TYPES OF PROPERTIES Physical Properties can be observed without changing a substance into another substance. (ex. boiling point, density, mass, or volume) 1 dm3 = (1 x 10-1 m)3 = 1 x 10-3 m3 DENSITY A chemical change alters the composition or identity of the substance(s) involved. An intensive property of a material does not depend upon how much matter is being considered. (ex. density, temperature, color) K = 0C + 273.15 1 L = 1000 mL = 1000 cm3 = 1 dm3 TYPES OF CHANGES A physical change does not alter the composition or identity of a substance. An extensive property of a material depends upon how much matter is being considered. (ex. mass, volume, length) 1 cm3 = (1 x 10-2 m)3 = 1 x 10-6 m3 • Any digit that is not zero is significant • Zeros between nonzero digits are significant • Zeros to the left of the first nonzero digit are not significant • If a number is greater than 1, then all zeros to the right of the decimal point are significant • If a number is less than 1, then only the zeros that are at the end and in the middle of the number are significant DIMENSIONAL ANALYSIS We use dimensional analysis to convert one quantity to another. desired unit given unit x = desired unit given unit 02 : ATOMS, MOLECULES, & IONS LAW OF CONSERVATION OF MASS: The total mass of substances present at the end of a chemical process is the same as the mass of substances present before the process took place. LAW OF MULTIPLE PROPORTIONS: If two elements, A and B, form more than one compound, the masses of B that combine with a given mass of A are in the ratio of small whole numbers. MOLECULES A molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical forces A diatomic molecule contains only two atoms Ex. H2, N2, O2, Br2, HCl, CO A polyatomic molecule contains more than two atoms Ex. O3, H2O, NH3, CH4 THE DISCOVERY OF ATOMS IONS An ion is an atom, or group of atoms, that has a net positive or negative charge. cation – ion with a positive charge If a neutral atom loses one or more electrons it becomes a cation. anion – ion with a negative charge If a neutral atom gains one or more electrons it becomes an anion. LIST OF COMMON IONS ▪ J. J. THOMSON – measured the charge/mass ratio of the electron to be 1.76 108 coulombs/gram through the cathode ray tube experiment ▪ ROBERT MILLIKAN - determined the charge on the electron in 1909 through the oil-drop experiment ▪ ERNEST RUTHERFORD - Rutherford postulated a very small, dense nucleus with the electrons around the outside of the atom thorough the gold foil experiment SUBATOMIC PARTICLES Mass Number A Atomic Number Z X Element Symbol WRITING FORMULAS Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons Isotopes are atoms of the same element (X) with different numbers of neutrons in their nuclei. Isotopes of hydrogen: 11 H 2H (D) 1 3H (T) 1 • • The charge on the cation becomes the subscript on the anion. The charge on the anion becomes the subscript on the cation. 03: CHEMICAL REACTIONS & STOICHIOMETRY STOICHIOMETRY: The study of the mass relationships in chemistry. CHEMICAL REACTION: A process in which one or more substances is changed into one or more new substances. CHEMICAL EQUATION: Uses chemical symbols to show what happens during a chemical reaction reactants products HOW TO BALANCE CHEMICAL REACTIONS? 1. 2. 3. 4. 5. Write the correct formula(s) for the reactants on the left side and the correct formula(s) for the product(s) on the right side of the equation. Change the numbers in front of the formulas (coefficients) to make the number of atoms of each element the same on both sides of the equation. Do not change the subscripts. Start by balancing those elements that appear in only one reactant and one product. Balance those elements that appear in two or more reactants or products. Check to make sure that you have the same number of each type of atom on both sides of the equation. THREE TYPES OF REACTIONS 1. COMBINATION: Two or more substances react to form one product. Examples: 2 Mg(s) + O2(g) N2(g) + 3 H2(g) C3H6(g) + Br2(l) 2 MgO(s) 2 NH3(g) C3H6Br2(l) 2. DECOMPOSITION: In a decomposition reaction one substance breaks down into two or more substances. Examples: CH4(g) + 2 O2(g) C3H8(g) + 5 O2(g) CO2(g) + 2 H2O(g) 3 CO2(g) + 4 H2O(g) 3. COMBUSTION: Generally rapid reactions that produce a flame. Most often involves oxygen in the air as reactant. Examples: CH4(g) + 2 O2(g) C3H8(g) + 5 O2(g) PERCENT COMPOSITION Percent composition of an element in a compound n x molar mass of element molar mass of compound x 100% where n is the number of moles of the element in 1 mole of the compound THE MOLE Mole (mol): A unit to count numbers of particles The mole (mol) is the amount of a substance that contains as many elementary entities as there are atoms in exactly 12.00 grams of 12C 1 mol = NA = 6.0221367 x 1023 INTERCONVERTING MASSES, MOLE, & ATOMS M = molar mass in g/mol NA = Avogadro’s number STEPS TO DETERMINE EMPIRICAL FORMULA REACTION YIELD Theoretical Yield is the amount of product that would result if all the limiting reagent reacted. Actual Yield is the amount of product actually obtained from a reaction. Limiting reagent is the reactant used up first in the reaction. % Yield = Actual Yield Theoretical Yield CO2(g) + 2 H2O(g) 3 CO2(g) + 4 H2O(g) MOLECULAR WEIGHT Molecular mass (or molecular weight) is the sum of the atomic masses (in amu) in a molecule. For any molecule molecular mass (amu) = molar mass (grams) x 100% STEPS IN STOICHIOMETRIC CALCULATIONS: 04 : REACTIONS IN AQUEOUS SOLUTIONS A solution is a homogenous mixture of 2 or more substances The solute is(are) the substance(s) present in the smaller amount(s) The solvent is the substance present in the larger amount ELECTROLYTES ACIDS AND BASES Arrhenius acid is a substance that produces H+ (H3O+) in water Arrhenius base is a substance that produces OH- in water Brønsted acid is a proton donor Brønsted base is a proton acceptor An electrolyte is a substance that, when dissolved in water, results in a solution that can conduct electricity. A nonelectrolyte is a substance that, when dissolved, results in a solution that does not conduct electricity. Strong Electrolyte – 100% dissociation NaCl (s) H2O Na+ (aq) + Cl- (aq) Weak Electrolyte – not completely dissociated CH3COOH REDOX REACTIONS CH3COO- (aq) + H+ (aq) Loss of electrons is oxidation. Gain of electrons is reduction. OXIDATION NUMBER OF EACH ELEMENT SOLUBILITY RULES Solubility is the maximum amount of solute that will dissolve in a given quantity of solvent at a specific temperature. OXIDATION NUMBER: The charge the atom would have in a molecule if electrons were completely transferred. SOLUTION STOICHIOMETRY PRECIPITATION REACTIONS Precipitate – insoluble solid that separates from solution precipitate Pb(NO3)2 (aq) + 2NaI (aq) PbI2 (s) + 2NaNO3 (aq) M = molarity = moles of solute liters of solution DILUTION Mc Vc = Md Vd where Mc and Md are the molarity of the concentrated and dilute solutions, respectively, and Vc and Vd are the volumes of the two solutions. 05: THERMOCHEMISTRY THERMOCHEMISTRY is the study of heat change in chemical reactions. The system is the specific part of the universe that is of interest in the study. CALORIMETRY The specific heat (s) of a substance is the amount of heat (q) required to raise the temperature of one gram of the substance by one degree Celsius. The heat capacity (C) of a substance is the amount of heat (q) required to raise the temperature of a given quantity (m) of the substance by one degree Celsius. open closed isolated mass & energy nothing energy EXOTHERMIC VS. ENDOTHERMIC PROCESS Exchange: C=mxs Heat (q) absorbed or released: q=mxsxDt q=CxDt D t = tfinal - tinitial HESS’S LAW If a reaction is carried out in a series of steps, DH for the overall reaction will be equal to the sum of the enthalpy changes for the individual steps. We can use Hess’s law in this way: DH = First law of thermodynamics – energy can be converted from one form to another, but cannot be created or destroyed. Esystem + Esurroundings = 0 or Esystem = -Esurroundings E=q+w nDH f,products – mDH ° f ,reactants where n and m are the stoichiometric coefficients. An enthalpy of formation, DHf, is defined as the enthalpy change for the reaction in which a compound is made from its constituent elements in their elemental forms. STANDARD ENTHALPIES OF FORMATION (298 K) E is the change in internal energy of a system q is the heat exchange between the system and the surroundings w is the work done on (or by) the system WORK w=Fxd w = -P DV ENTHALPY When the system changes at constant pressure, the change in enthalpy, DH, is DH = DE + PDV Since DE = q + w and w = −PDV, DH = DE + PDV DH = (q + w) − w DH = q Enthalpy of reaction: So, at constant pressure, the change in enthalpy is the heat gained or lost. DH = Hproducts − Hreactants SIGN CONVENTIONS REMEMBER: The standard enthalpy of formation of any element in its most stable form is zero.
