General chemistry 2 reviewer, Study notes of Chemistry

Download General chemistry 2 reviewer and more Study notes Chemistry in PDF only on Docsity! WEEK 1: INTERMOLECULAR FORCES Solid - The molecules in a solid are closely packed together and contain the least amount of kinetic energy. Liquid - A nearly incompressible fluid that conforms to the shape of its container but retains a constant volume independent of pressure. Gas - A substance that has no fixed size or shape Intramolecular Forces ● force within a molecule, that holds the atoms together ● Strong bond Intermolecular Forces ● Attractive Force between molecules ● Weak bond UNDER INTERMOLECULAR FORCES: Ion-dipole Interactions ● Responsible for dissolution of most ionic solids in solar solvents ● Ions are bonded with partial – + (polar) Dipole-Dipole ● Polar molecules – Dipoles ● forces exist between molecules that are polar Hydrogen Bonding ● Hydrogen is present ● Hydrogen is bonded to most electronegative atoms namely F, O, or, N. ● In bonding of water, one molecule of hydrogen is attracted to the Oxygen atom of molecule London Dispersion Forces ● Weakest type ● Present in between electrically neutral molecules ● Named after Fritz London ● force occurs between mainly nonpolar molecules and also between noble gas atoms Properties of liquid Water ● Water is a good solvent, Has a high specific heat ( is the amount of heat or energy needed to raise the tempera-ture of one gram of a substance by 1oC) ● Intermolecular forces are directed to surface tension, viscosity, vapor pressure of the liquid PROPERTIES: Surface Tension ● Tendency of a fluid to acquire the least possible surface area, i s the measure of the elastic force on the surface of a liquid. the stronger the intermolecular forces, the higher the surface tension Cohesion ● Attraction of like molecules, forces are those that hold the body of a liquid together Adhesion ● Attraction of unlike molecules, are those that try to make a body of a liquid spread out Viscosity ● Measure of fluid’s resistance to flow ● Liquids flow easily have low viscosity , Liquids do not flow easily have high viscosity ● Strong intermolecular forces have greater resistance to flow due to difficulty of molecules to move. Capillary action - is the tendency of a liquid to rise in narrow tubes or be drawn into small openings such as those between grains of a rock Vaporization ● fraction of kinetic energy of liquid escapes to the surface to enter vapor phase Enthalpy of vaporization ● the quantity of heat that must be absorbed if a certain quantity of liquid is vaporized at a constant pressure Vapor Pressure ● Pressure exerted by a vapor in equilibrium with liquid phase in a closed system . ● Molecules with strong IMFA have less tendency to escape into gas, lower vapor pressure compared to weaker IMFA Solubility ● To dissolve in a given amount of solvent at a specified temperature. Miscible liquids ● two liquids dissolve or mix together Immiscible Liquids ● 2 liquids do not dissolve or mix together Boiling Point ● Liquid to gas ● is the temperature at which the liquid converts into a gas WEEK 2: PHASE CHANGES: Phase Diagrams AMORPHOUS SOLIDS ● molecules or atoms do not have a definite lattice pattern or not organized CRYSTALLINE SOLIDS ● makes up solid in a regular, well-defined arrangement - REGULAR Phase changes ● Changes of energy and intermolecular force ● are accompanied by a change that occurs as a result of energy interactions and the intermolecular forces in the substance itself. Curves Melting (or freezing curve) ● The curve, on a phase diagram which represents the transition between the liquid and solid states. Vaporization (or Condensation) curve ● The curve on a phase diagram which represents the transition between the gaseous and liquid states. Sublimation (or Deposition) Curve ● The curve on a phase diagram which represents the transition between the gaseous and solid states. Heat of fusion ● ∆H fus ● Amount of heat needed to melt a substance Points TRIPLE POINT - The point on a phase diagram at which the three states of matter coexist. CRITICAL POINT - The point in temperature and pressure on a phase diagram where the liquid and gaseous phases of a substance merge together into a single phase. Melting Point ● Temperature when substance melts Freezing point ● Liquid to gas at a constant temperature Boiling point ● Liquid – gas Phase Transition -is the physical process of transition between one state of a medium and another. Heat Capacity - defined as the amount of heat to be supplied to an object to produce a unit change in its temperature. Heat of Fusion -is a quantity of energy needed to melt or freeze a substance under conditions of constant pressure. Heat of Vaporization -is the amount of energy that must be added to a liquid substance to transform a substance into a gas. Heat of Solidificatio n -the heat liberated by a unit mass of liquid at its freezing point as it solidify Heat of Condensation -heat evolves when a vapor changes to a liquid. Latent Hea t- is the heat required for an object to change phase WEEK 3: CONCENTRATION OF SOLUTIONS olution ● Homogenous mixture ● Consist of solute and solvent Unsaturated Solution ● Solute is less than solvent Saturated Solution ● Solute is equal to solvent’s solubility Supersaturated ● Solute is greater than solvent’s solubility ● Dissolving solute at higher temperature, subsequently cooling it down Diluted ● Lower concentration ● Lower amount of solute Concentrated ● High concentration ● Large amount of solute Concentration ● Intensive property ● Expresses the ratio of the amount of the solute Percentage by mass (% m/m) ● mass percent or weight percent (% w/w) ● the mass of solute per mass of the solution ● mass fraction times 100. ● should be expressed in the same units. x 100 % 𝑚 𝑚 = 𝑚𝑎𝑠𝑠 𝑠𝑜𝑙𝑢𝑡𝑒 𝑚𝑎𝑠𝑠 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 Percentage by volume(% v/v) - volume percent - the volume of solute per volume of the solution. - expressed as the volume fraction times 100 x 100 % 𝑚 𝑚 = 𝑣𝑜𝑙𝑢𝑚𝑒 𝑠𝑜𝑙𝑢𝑡𝑒 𝑣𝑜𝑙𝑢𝑚𝑒 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 Percentage by mass per volume(% m/v) ● The mass of the solute is usually expressed in grams. ● The volume of the solution is usually expressed in millimeters . x 100 % 𝑚 𝑚 = 𝑚𝑎𝑠𝑠 𝑠𝑜𝑙𝑢𝑡𝑒 𝑣𝑜𝑙𝑢𝑚𝑒 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 Molarity(M) WEEK 5: ENTHALPY OF REACTIONS Energy ● Capacity to do work ● Present in all chemical & physical processes ● converted from one form to another Enthalpy Change ● heat of reaction, heat content at constant pressure ● IS A MEASURE OF THE AMOUNT OF HEAT TRANSFERRED INTO OR OUT OF A SYSTEM. (H) Thermochemistry ● Study of heat changes in chemical reaction, is the branch of thermodynamics that deals with the heat absorbed or produced by a chemical reaction. A reaction can be either: Exothermic - the one that releases energy (-ΔH) Endothermic - the one that absorbs energy (ΔH) ΔH = E + PΔV H=enthalpy E=internal energy P=const. pressure V=volume Enthalpy is a state function which means the energy change between two states is independent of the path. Thermochemical equations- can be manipulated to give important data about chemical reactions. Law of conservation of energy ● Energy is not created nor destroyed ● Governs all transformations of energy 1st law of thermodynamics ● Energy is neither created nor destroyed ● Etotal always same = energy conserved System ● gas inside cylinder Internal Energy ∆USystem = q(heat) + w(work) Enthalpy of reactions Calculate the enthalpy of combustion of methane, if the standard enthalpies of formation of methane, carbon dioxide, water are −74.85,−393.5 and −286? System ● portion under study Surroundings ● not part of the system Amount of energy in system: ● ∆U = q + w for pressure-volume work ● ∆U = q - P∆V Joule ● unit for enthalpy Hess’s Law ● an extension of the law of conservation of energy ● states that the total enthalpy change for a reaction is the same, regardless of the path taken to reach the final state. This means that if a chemical reaction can be broken down into several steps, the enthalpy change for the reaction is equal to the sum of the enthalpy changes for each of the steps. Standard state - physical state under standard conditions - 1 atm and 298 K Calculate the enthalpy change for reaction using enthalpies of formation WEEK 6: RATE OF REACTION REACTION RATE AND FACTORS AFFECTING IT Chemical Kinetics ● how fast a reaction can occur ● the rate of reaction rate at which the products are formed or reactants consumed ● study of reaction mechanisms ● series of steps that take place in a chemical reaction Nature of Reactants ● Reactivity of the reacting species affects the rate of reaction. ● ↑ reactivity = ↑ rate of reaction ○ Group 1 metals are more reactive than Group 2 elements. Surface Area ● The rate of a reaction also depends on how well the reactants mix. ● ↓ particles = ↑ surface area ● ↑ surface area = ↑ reaction rate Temperature ● an increase in temperature is accompanied by an increase in the reaction rate. Temperature is a measure of the kinetic energy of a system, so higher temperature indicates higher average kinetic energy of molecules and more collisions per unit time. REACTION RATE ● Related to the change in concentration of reactants or products over time ● not constant ● reactants: decrease in amount ● products: increase in amount ● conventionally written as a positive number ● reactants decrease in amount with time, therefore final amount is less than initial amount RATE ● Types: Average, Initial, and Instantaneous AVERAGE RATE ● Dependent on specific time interval ● Typically, only two concentration values are considered—initial and final concentrations for a given time interval only. INSTANTANEOUS RATE - Rate at a specific point in time ORDER OF RATE AND REACTION LAW ● RATE LAW - rate of a reaction as a function of concentration at a specific temperature. - The concentration of the products does not affect the rate of the reaction. Orders of the reaction (m, n) ● shows the concentration dependence of reaction rate. ● reaction order is not equal to the stoichiometric coefficients unless the reaction consists of a single elementary step. ● The overall order of a reaction is the sum of the reactants individual order. FIRST ORDER REACTION ● A reaction is considered first-order if the rate is directly proportional to the concentration. ● which the reaction rate is linearly dependent on the concentration of only one reactant. A first-order reaction is a chemical reaction in which the rate varies based on the changes in the concentration of only one of the reactants. Thus, the order of these reactions is equal to 1. SECOND ORDER REACTION ● A reaction is considered second-order if the rate is directly proportional to the square of the concentration. ● depend on either the concentrations of two first-order reactants or the concentration of one-second order reactants. ZERO ORDER REACTION ● A reaction is considered zero-order if the rate does not depend on concentration. ● is a chemical reaction wherein the rate does not vary with the increase or decrease in the concentration of the reactants. Therefore, the rate of these reactions is always equal to the rate constant of the specific reactions ● METHODS OF INITIAL RATE: ● To determine the reaction orders, a series of experiments is performed where one reactant concentration is varied while the others are kept constant. ● For each experiment, the effect of the concentration change on the initial rate is measured. WEEK 7: REACTION RATE - CATALYST AND COLLISION THEORY Collision Theory ● The molecules involved in the reaction must have a redistribution of energy between them to break bonds. predict the rates of chemical reactions ● based on the assumption that for a reaction to occur it is necessary for the reaction species to collide with one another. ● This energy should be sufficient to break the bonds. Activation energy ● The minimum kinetic energy the molecules should possess to produce a chemical reaction. ● minimum amount of energy needed to activate or energize molecules or atoms so that they can undergo a chemical reaction ACTIVATED COMPLEX IS AN UNSTABLE ARRANGEMENT OF ATOMS THAT EXISTS MOMENTARILY AT THE PEAK OF THE ACTIVATION ENERGY BARRIER. Two factors 1.The collision must involve enough energy to produce the reaction. 2. The reacting molecules collide in the proper orientation for new bonds to form INEFFECTIVE COLLISIONS- ARE THE COLLISIONS IN WHICH THESE TWO CONDITIONS ARE NOT SATISFIED SO A REACTION DOESN'T TAKE PLACE. EFFECTIVE COLLISIONS - ARE THE COLLISIONS IN WHICH THESE TWO CONDITIONS ARE SATISFIED SO A REACTION OCCURS. TRANSITION STATE THEORY ● A transitory state exists where all bonds involved in the reaction are broken and formed simultaneously ● The state is called the transition state. ● The chemical species involved is the activated complex. ● Three major factors to determine whether or not a reaction will occur: (1) The concentration of the activation complex, (2) The rate of decomposition of the activation complex, (3) Whether the reactants or products are formed after decomposition ● The difference between the energy of the reactants and the highest energy in the reaction is the activation energy. TAKE NOTE: ● The molecules in collision should have sufficient energy to overcome the activation energy barrier. ● The molecules should be in proper orientation upon collision for a reaction to proceed to completion. CATALYST ● substances that alter the rate of chemical reactions without being chemically changed themselves. ● offers an alternative reaction pathway with lower activation energy ● not consumed in the reaction ● does not appear in the balance chemical equation CATALYTIC REACTION ● Enables more particles to produce successful collisions. Catalyzed Reactions - are reactions with a catalyst. . Enzymes- are biological proteins, and they are called biological catalysts that enhance the reactions in biological systems. Uncatalyzed Reactions - are reactions without a catalyst. Heterogeneous Catalyst ● occupies a different phase compared to the reactant molecules ● when the catalyst and the reactant are in different phases. ● easily recovered Homogeneous Catalyst ● occupies a same phase compared to the reactant molecules ● reactions where the catalyst is in the same phase as the reactants ● typically observed in aqueous and gas phase ● ACIDS AND BASES Heterogenization of homogeneous catalytic system - is a modification of homogeneous catalysts to “break” the uniformity among the molecules of the catalyst and the product by rendering them in separate phases to allow their separation. Biocatalyst is the substance, such as enzymes or hormones, that initiates or increases the rate of chemical reaction. Positive catalyst increases the rate of the reaction by providing a shorter path to the reaction to take place. Negative catalyst decreases the rate of the reaction by providing a longer path for the reaction to take place. Auto-catalyst the product formed in the reaction acts as catalyst for the reaction to proceed. Chlorofluorocarbons (CFCs) ● used as refrigerants when exposed to UV rays in the atmosphere produce chlorine radicals. ADVANTAGES : ● high reactivity & high selectivity ● mechanisms are studied better ○ ease of controlling reaction condition and parameter DISADVANTAGES: ● difficult recovery of catalyst ○ requires complex separation techniques REMEMBER : ● Homogeneous catalysts : same phase as the reactants ● Heterogeneous catalysts : different phase as the reactants ENZYMES Criteria Inorganic Catalyst Enzyme Function Catalysts increase the rate of a chemical reaction but remain unchanged. Enzymes increase the rate of chemical reactions converting substrates into products Molecular Weight Low molecular weight substances High molecular weight globular proteins Nature Simple Inorganic Molecules Complex Proteins Reaction Rate Slower than Enzymes Several times faster than inorganic catalyst Specificity Not specific HIghly specific