More Chem

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Phase Change

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A change in the state of matter. This change is a physical one, not a constant one. This is a reversible change in molecular interactions. Can be either endothermic or exothermic. This is based on whether or not the final state is of a higher or lower energy. A change in volume and a change in shape.

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Change in Enthalpy

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A change in heat energy

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Change in Entropy

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Entropy is also known as the "randomness." This is a change in the organizational potential energy.

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Vaporization

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Phase change of liquid to Gas. +ΔH vap. +ΔS

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Condensation

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Phase change of gas to liquid. -ΔH vap. -ΔS

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Melting

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Phase change of solid to liquid. +ΔH fusion. +ΔS

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Freezing

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Phase change of liquid to solid. -ΔH fusion. -ΔS

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Sublimation

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Phase change of solid to gas. +ΔH sub. +ΔS.

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Deposition

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Phase change of gas to solid. -ΔH sub. -ΔS.

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Energies for the phase change processes relative to one another

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Sub >Vap > Fusion for both ΔH and ΔS

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Isothermal

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k

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Isobaric

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k

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Isocharic

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l

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Adiabatic

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k

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Critical Point

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This is the point at which we no longer see a difference in characteristics between a liquid and a gas. At the critical point no amount of pressure increase will cause the gas to liquid phase change to occur. Also the highest temperature and pressure at which a liquid can be observed. Beyond this point we cannot distinguish between a gas and a liquid.

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Phase of a substance at boiling, melting, sublimation points

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The substance is able to exist as EITHER of the two phases at this point. For example, a liquid exists as both liquid and vapor because there is an equilibrium between evaporation and condensation that contributes towards vapor pressure.

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Role of Heat Energy in Phase Change

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Applied heat energy can either work towards increasing kinetic energy and thus causing a temperature change, or a phase change.

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Relationship between vapor pressure and temperature and ΔH

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When temperature increases, vapor pressure also increases. When ΔH vapor increases, the vapor pressure decreases. ΔH is the energ that is needed to overcome intermolecular forces. If we require more energy in order for molecules to leave the liquid and join the vapor, then we will have a lower pressure of vapor.

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Vapor Pressure

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Pressure of molecules above a liquid that is at equilibium between vaporization and condensation.

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Boiling Point

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Temperature above which a substance cannot be a liquid. Occurs when the atmospheric pressure is equal to the vapor pressure. Thus, when we have atmospheric pressure conditions changing, then we will have changes in the boiling point.

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Melting Point

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Vapor pressure of liquid is equal to vapor pressure of solid.

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How do HCL, HBr, and HI differ in BP

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The greater the molecular mass, the greater the boiling point. The substance with a greater molecular mass is harder to vaporize.

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Relationship between Hydrogen Bonding and BP

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The less hydrogen bonding there is within a compound, the lower the boiling point. The intermolecular forces are easier to overcome to get molecules to vacate the liquid phase and join the vapor contributing to vapor pressure.

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Colligative Property

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A colligative property is a solution property that is affected by the concentration of soluble impurities.

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Boiling Point Elevation

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When the concentration of impurities increases, the boiling point increases. In water we see this because the bonds between water and other ions are stronger than water/water bonds. Equation: ΔTb = kbxixm

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Freezing Point Depression

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When the conentration of impurities increases, the freezing point decreases.

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Osmotic pressure

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Osmosis is the process by which water flows from a lower solute concentration to a higher colute concentration. = MiRT. When osmotic pressure = hydrostatic pressure water stops flowing. Hydrostatic pressure = density x g x Δ

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Aicd Dissociation

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When an acid dissociates into its ion components when placed in water.

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Acid Dissociation Constant

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Ka. Follows the rules of the equilibrium constant. From this we can find the pKa, which = -log(Ka). Ka = 10^-pKa

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Base Hydrolysis

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When a base is placed into water, the base hydrolyzes. Separates into its ion components. This is expressed with Kb the base constant. Follows the same equations that related to Ka.

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Relationship between acid/base strength, Ka/Kb, pKa/pKb

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As the strength increases the Constant increases, and the pConstant decreases. As acid/base strength increases, the conjugate base/conjugate acid strength decreases.

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pH equation for weak acids and bases

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There is no complete dissociation, therefore we use equilibriam constants to determine the concentration of H+ and OH- . pH = (1/2)pKa - (1/2)log[HA]

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Equilibrium Constant

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Is the K-Value. The K Value is found by using the law of mass action. For a complex equilibrium where you have equilibriums that are interconnected, the product of one is the reactant of the other and you will multiply the equilibrium constants together.

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Law of Mass Action

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We get [products]/[reactants] all raised to the stoichiometric coefficients. We can use this in order to predict shifts. In the equilibrium.

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Predicting Shifts using Keq

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We use the law of mass action. We use the initial concentrations, the proposed shift on both sides, and what we will have at equilibrium using values of X for the change. We put X into the equilibrium equation and solve for it in order to determine what the shift is and what we have at the end. On the multiple choice exam you can substitute the given answers into the equation to see which is right.

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Solubility Rules: Salts made of +1 cation/-1 anion

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: soluble at room temp.

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Solubility Rules: Nitrate

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NO3-: large anion. Weak lattice interactions. Most of its salts are water soluble. Forms stron ghydrogen bonds with water.

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Solubility Rules: Sulfate anions

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So4^2-: With +1 cations are water-soluble.

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Solubility Rules: Salts with -2 or -3 anions

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insoluble in water. This excludes sulfate salts.

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Solubility Rules: Oxide and Hydroxide anion salts

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O^2-/OH- : only slightly water-soluble. KOH and NaOH - exceptions that are very soluble.

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Acetate

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C2H3O2-

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Bicarbonate

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HCO3-

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Bisulfite

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HSO4-

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Dihydrogen phosphate

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H2PO4-

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Hypochlorite

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ClO-

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Chlorite

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ClO2-

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Chlorate

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ClO3-

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Perchlorate

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ClO4-

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Cyanide

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CN-

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Hydroxide

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OH-

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Superoxide

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O2-

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Nitrite

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NO2-

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Nitrate

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NO3-

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Permanganate

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MnO4-

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Carbonate

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CO3^2-

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Chromate

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CrO4^2-

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Dichromate

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CrO4^2-

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Hydrogen Phosphate

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HPO4^2-

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Oxalate

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C2O4^2-

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Oxide

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O^2-

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Peroxide

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O2^2-

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Sulfite

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SO3^2-

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Sulfate

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SO4^2-

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Phosphate

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PO4^3-

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Ammonium

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NH4+

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Ksp

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Solubility Product - The equilibrium constant that relates to solubility. Solved by the law of mass action. Can be used to determine the molar solubility.

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Molar solubility

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Solve for X the same way that we do for the equilibrium shifts. When you solve or x you determine the molar solubility. This is based on the Ksp expression. When you are solving for solubility - YOU MUST MULTIPLY AND RAISE TO THE POWER OF THE COEFFICIENT. when translating from the equation for the reaction to the law of mass action.

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Common Ion Effect

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Reduction in solubility of an ionic solid (salt) in solution because one of the ions in salt is already present in solution. Adding ions of the dissolution results in a leftward shift towards the reactants, which causes more precipitate (solid) and reduces the solubility of the salt.

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Electrochemistry

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Examination of the chemical reactions where there is a transfer of electrons. These types of reactions are known as redox reactions. Electrochemistry studies this energy transfer.

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Redox Reactions

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A redox reaction has to do with a transfer of electrons from one species to another. A Reduction (gain of electrons) and an oxidation (loss of electrons). These two processes always happen in pairs. Has the biggest change in Free Energy and Enthalpy of most of the reactions we learned about. Many power sources rely on redox reactions for energy to function. The energy of the electron flow can be used for mechanical work, heat, light, translational energy of particles.

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Electrochemical Cells

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Function as a means to harness the energy of the electron transfer. Separates the half of the reaction that is an oxidation from the half of the reaction that is a reduction. Electrons must be transferred through a wire.

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Electromotive Force

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Is the voltage available due to a chemical reaction.. Determines the cell voltage, which can be converted into an energy amount that is proportional to the number of electrons. IS the

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Voltage

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Units: J/C. Energy is released as electrical flow, which is harnessed in voltage. Voltage is the potential difference between two points. Causes a current. The two points must have a conducting medium between them.

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When does a 1/2 reaction proceed more favorably

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Both Oxidation and Reduction half reactions proceed more favorably when there is a positive potential for the related action. Oxidation reaction: positive oxidation potential.

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What do higher Emf values correspond to

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More favorable half reactions (related to the potentials of the tables) . The strongest oxidizing agent will undergo the most favorable reduction half reaction and have the greatest electromotive force.

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Cell Potential

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Is the sum of the electromotive force of the reduction and the oxidation.

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Free Energy in an Electrochemical Cell

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Tells us whether the cell reaction is spontaneous or not. Like with other reactions, a negative free energy indicates that we have a favorable redox reaction. A positive change in electromotive force indicates a favorable redox reaction as well. The equation for Free Energy Change = -nFE (E= electromotive force, n = electrons/reaction, F = 965000 C/mole)

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Electrochemical Cell Again

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Converts energy from a chemical reaction to electron flow (current). That is the purpose so that we can harness the large amounts of energy produced by the redox reaction. Accomplished by separation the oxidation and reduction half reactions, and connecting them w/ conducting material. Reaction results in an electrical flow from reducing agent to oxidizing agent.

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Components of the electrochemical cell

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Oxidation cell: Anode Point of roxidation. The anode is the reducing agent. Electrons flow away from the anode. Reduction cell: Cathode. Point of reduction. Electrons flow toward the cathode. Anions migrate towards the anode. Cations migrate towards the cathode. Wire connects the two cells. Salt bridge.

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Cathode

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Pint of reduction half reaction. Direction towards which electrons flow. Has a positive core. Accumulates negative charge on the surface.

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Anode

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Point of oxidation. Electrons flow away from the anode. Has a negative core. Accumulates positive charge on its surface.

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Salt Bridge

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Permits the flow of anions. In the direction opposing the electron flow. This balances out the charge distribution with electron flow. If there is no salt bridge the electrons will not flow through the conducting material, and the reaction will not proceed.

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Galvanic Cell

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Discharges voltage and harnesses energy. Has a negative free energy change and a positive emf, therefore the reaction proceeds favorably. Convention: Anode on the left. Cathode on the right.

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How to increase voltage in the Galvanic Cell

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The more that a reaction can proceed in the forward direction, the grater its voltage. Therefore, if we increase the ions in the cathode solution and decrease ions in the anode solution, then we will increase voltage.

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Electrolytic Cell

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A chemical reactionthat occurs in a thermodynamically unfavorable directon. This requires energy. Thus, an electrolytic cell involves a voltage source. The applied voltage is greater than the natural voltage. This forces the reaction to move in a reverse direction. If the applied voltage is not large enough, tehn the reaction won't proceed and no charge is stored.

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Battery

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A galvanic cell or a series of galvanic cells. Uses reversible redox reaction. It discharges current and releases voltage - galvanic cell. Apply voltage, recharges and absorbs current - electrochemical cell.