Chemistry Cheat Sheet. 6.022X1023 atoms in 1 mol. Ester – an organic compound responsible for the aromas and flavors of fruits. An excess reactant is not completely used up in a chemical reaction; some will be left over after the reaction is complete. A limiting reactant is used up first and limits the amount of other reactants that can participate in a chemical reaction. To figure out which is limiting reactant: figure out how many moles of each reactant are present, figure out how much of each reactant is needed for the other reactant. If you need more than what’s already given, it’s the limiting reactant. To reactant. To get theoretical yield, use the limiting reactant to find the amount of product. Percent yield : actual yield/theoretical. 1 mol at STP = 22.4 L Heat is measured in Joules. Heat (thermal energy) is total random kinetic energy of its atoms. Atoms move faster at high temp. No negative temperatures temperatures on Kelvin scale (can’t have negative motion). Heat capacity (C)- thermal energy needed to raise an object’s temperature by 1K. q = nC T [[q=heat needed, n=moles]] Enthalpy(H) - the heat, or thermal energy, of a substance. Change in enthalpy H can be measured when a substance is heat/cooled. All elements under standard conditions have molar enthalpy of 0. Enthalpy- energy that’s “INSIDE” an object or substance. Entropy(S)- measures the AMOUNT OF DISORDER of material present. Enthalpy and Entropy are extensive properties, which depend on how much material is present. Extensive properties: mass, volume, heat capacity, enthalpy, entropy. Intensive: density, pressure, temp, concentration. concentratio n. H = nC T/n. Under standard conditions: H°= sum of H° products – sum of H° reactants. S° = sum of products – sum of reactants. Molar heat capacity measured in Joules/K*mol. If G is negative, then process process is SPONTANEOUS/ SPONTANEOUS/ EXOTHERMIC. EXOTHERMIC. If it’s POSITIVE, it’s not spontaneous/ENDOTHERMIC. The effect of changes in H & S on change in free energy: Neg egat ativ ive e H (e (exo xo)) Pos osiitiv ive e S(d S(dis isor ord der erin ing gN ) egative G Spontaneous at all temp G = H T S Negative H (exo) Negat atiive S (or (ord deri rin ng) Neg Ne gat atiive ve//Pos osit itiv ive eG Low Lo w tem temp perat atu ure G = - spon Positive H (endo)
Positive S
Neg/Pos G
High temperature
Positive H
Negative S
Positive
Never spontaneous
G= + non-
Hess’ law says that any two processes that start with the reactants in the same condition and finish with the products in the same condition will have the same enthalpy change. Kinetic Molecular Theory-explains behavior of gases at molecular level. The temperature of a gas determines the average kinetic energy of its particles. Standard Temperature and Pressure (STP) for a gas is 0° and 1 atm. Greenhouse effect- increase in temp. of earth caused by reflected solar radiation that is trapped in the atmosphere. Ultraviolet Radiation is a mutagen because it can cause mutation. Free radical- atom or molecule that has one or more unpaired electrons and is therefore very reactive. P= pressure exerted by particles. V= volume occupied. T= temp in Kelvins. n= number of moles. Volume is inversely proportional to pressure. Pressure of gas increase, volume decrease. Boyle’s Law – volume of a given amount of gas at constant temp. is inversely proportional to pressure : P1V1=P2V2 Partial pressure- the pressure of an individual gas in a gas mixture that contributes to the total pressure of the mixture. DALTON’S LAW OF PARTIAL PRESSURE- total pressure is sum of partial. Ptotal= PA+PB+PC Mole Fraction- # of moles of one component compared with total # of moles expressed in ratio. Mol Fraction = MolA/MolA MolA/MolA +B+C. Heating gas will make it expand. CHARLES’ LAW – the volume of a sample of gas at constant pressure is directly proportional proportional to absolute temp. V1/T1 = V2/T2 Gas pressure INCREASE, temperature INCREASE. Avogadro’s Law – equal volumes of different gases under the same conditions of temp and pressure have the same # of molecules. STP = 101.3kPa, 1 atm, 0°C, 273K, 760mmHg. DIFFUSION- process by which particles mix by dispersing from regions of higher concentration concentration to regions of lower concentration. concentration. Colloid – a mixture in which small particles are suspended throughout a solvent. MOLARITY = MOL / L. Electrolyte – a substance, substance, that when dissolved dissolved in a solvent, increases that solvent’s + conductivity. Hydronium ion: H 3O . Colligative Properties depend only on the concentration of the solute particles (boilingpoint elevation and freezing-point depression). Le Chatelier’s Principle tells how a system at equilibrium reacts to an applied stress (change temp or pressure of the system or change in concentration of a component). K eq = products/reactants. The coefficients would be exponents and H 2O isn’t counted. Solubility-product constant is the equilibrium constant for a slightly soluble ionic solid with its ions in a saturated solution. K sp = [products in aqueous]. A strong acid ionizes completely; a weak acid is a weak electrolyte. Strong acids: HClO3, HCl, HNO3, H2SO4. Weak acids: CH3COOH, H3PO4, H2SO3. Carboxylic acid is an organic compound that contains the carboxyl functional group. –C- O - with double bond to O on top. A base that dissolves easily in water is called an ALKALI and the resulting solution is called ALKALINE. Strong bases: Ba(OH)2, KOH, NaOH, Na3PO4. Weak bases: NH3, Na2CO3. K w= 1X 10-14. Kw= [H3O+][OH-]. A Brønsted-Lowry acid DONATES a proton to another species. A Brønsted-Lowry base RECEIVES a proton from another species. Amphoteric Amphoteric is any molecule that can act as a base or an acid. K A is the acid-ionization constant or the equilibrium constant for a reaction in which an acid donates a proton to water. pH = -log[H3O+]. IF ___ IS A STRONG ACID, THEN THE HYDRONIUM ION CONCENTRATION EQUALS THE CONCENTRATION OF THE SOLUTION. pOH + pH = 14. When you calculate the –log[H3O+], you get pH. But when you calculate –log[OH -], you get pOH. Equivalence point: the point in a titration when the amount of added base/acid is equal to amount of acid/base originally in solution. Titration = gradually adding one solution to another to reach equivalence point. REACTION RATE is the decrease in reactant concentration or increase in product concentration per unit of time as a reaction proceeds. Rate can be noted from disappearance of a reactant or the appearance of a product. The SLOWEST STEP in the mechanism of a reaction is the rate-determining step. Intermediates (formed in one step but consumed in a later step) do not appear in a rate law expression. Rate law: Rate = k[a]n Things that affect reaction rates : nature of reactants, surface area of solids, concentration concentration of reactants, temperature of reactants, && catalysts. OXIDATION-REDUCTION REACTIONS : chemical changes that occur when electrons are transferred between reactants reactants (also called “redox reactions”). NO REDUCTION, NO OXIDATION. Oxidation is complete or partial LOSS of electrons or GAIN of oxygen. Reduction is complete or partial GAIN of electrons or LOSS of oxygen. Reducing agent = donates electron. Oxidizing agent agent = accepts electron. electron. If it’s oxidized, it’s
the reducing agent. If it’s reduced, it’s the oxidizing agent. Higher electronegativity gets reduced (increases up, and to the right). Rules for assigning oxidation numbers: 1. Oxidation # of hydrogen is always +1 except in metal hydrides. 2. Oxidation # of Oxygen is always -2 except in peroxides when it’s -1. The oxidation-number change method and the half reaction method are based on the fact that the total number of electrons gained in reduction must equal the total # of electrons lost in oxidation. Oxidation-number change method: a redox equation is balanced by comparing the increases and decreases in oxidation numbers.