Electrolysis: the process of creating an electrolyte cell ○ Used for electroplating Electrolyte cell: runs by running a galvanic cell backwards → the electrons are flowing in the opposite direction ○ In galvanic cells, electron flow is a...
As the cell runs, the redox reaction is getting back to equilibrium Any Ecell value anything other than 0 is running and producing voltage → A running galvanic cell is NOT at equilibrium! A dead battery is a galvanic cell that has reached equilibrium (Ecell = 0V and Q...
Cell potential or electromotive force: the “pull” or driving force on the electrons ○ Substance being oxidized “pushes” the electrons ○ Substance being reduced “pulls” the electrons thru the wire Ecell is measured in Volts (V) using a...
Galvanic cell = battery → provide power REDOX reactions can be used to convert chemical energy into electrical energy ...
Can “couple” an unfavorable reaction with a favorable reaction to make the overall process favorable ○ Must have a common intermediate (was a product in one reaction and then became a reactant) and when coupled yield an overall reaction with a negative...
Free Energy at Nonstandard Conditions Enthalpy does not depend on volume or pressure, but entropy does ○ Positional probability: A decreasing ΔG means that the favorability of the forward reaction is increasing (reaction shifts right) An increasing ΔG...
A thermodynamically favored reaction does not always occur or may occur at extremely slow rates ○ System is described as being under “kinetic control” ■ Often due to a high activation energy Note: adding a catalyst has not effect on the values of ΔH°...
Gibbs Free Energy and Thermodynamic Favorability Gibbs Free Energy: available energy of substance that can be used for work ○ Used to predict if a chemical reaction will occur spontaneously -ΔG° = thermodynamically favored ○ The reaction favors the products +ΔG° =...
The Third Law of Thermodynamics: the entropy of a perfect (ionic) crystal at 0K is zero bcus there is NO disorder (everythings is positioned perfectly) ○ S values at other temps must be higher Standard Entropy Standard Entropies S° (at 298K and 1 atm) (must...
Thermodynamics let us predict whether a process will occur but does not tell us about the amount of time required A spontaneous or “thermodynamically favored” process is one that occurs without intervention; the reaction rate may be fast or slow ○ Ex: a ball rolls...
Buffer capacity: represents the amount of H+ or OH- the buffer can absorb without a significant change in pH The buffer capacity is determined by the [A-] & [HA] (molarity) ○ More moles = greater capacity ○ Less moles = less capacity bcuz there...
○ Is only used to determine the pH of a buffer system ○ Can be molarity, moles or mmols of A- & HA The pH of a buffered solution is determined by the ratio of [A-]/[HA] ○ What if the acid and conjugate base are equal in...
What is a Buffer? A weak acid and its conjugate base together ○ Conjugate base usually present within a salt A weak base and its conjugate acid together The purpose of a buffer is to resist changes in pH when either H+ or OH- are added Write the Reaction of… Adding a...
pH and pKa If you know the pH and pKa on an environment, you can know the ratio of [A-]/[HA] ○ If the ratio of [A-]/[HA] is > 1 → [HA] < [A-] & pH > pKa, ○ If the ratio of [A-]/[HA] is < 1 → [HA] > [A-] & pH < pKa...
Note: stronger acid/base = less stable X-H Acids For X-H acids, there are two factors for acid strength Bond Strength (between H and other atom): low = strong acid bcuz H can easily dissociate Compare bond dissociation energies 2. Bond Polarity (high → weak acid) The...
In acid-base titrations/reactions, are dealing with neutralization reactions (Use NmN Tables→ water is not a reactant) ○ N: neutralization reaction ○ M: mmols ...
Acid Dissociation Constant For weak acids only: (note [H+] is the same as [H3O+]) ○ Strong acids don't have Ka Larger Ka = stronger weak acid → will produce more H3O+ ions and thus a lower (more acidic) pH Weak Acids Any acid that is not one of the 6...
Strong Acids Strong acids dissociate completely → reaction will go to completion [H+] = [HA] → molarity of H+ = molarity of the strong acid Strong Acids to know: HCl, HClO4 (Perchloric), HI, HBr, H2SO4 (Sulfuric), HNO3 (nitric) ○ Any other acid is a weak...
Acids All acids start with H Covalent bonds bcuz hydrogen bonds with nonmetals Can usually tell that is an acid b/c produces H+ in solution Naming acids Binary: hydro___ic acid Polyatomic: NO hydro ○ -ate = __ic acid ○ -ite = __ous acid Bases...
The solubility of some salts is affected by the pH of the environment Basic Solutions High pH (more basic) → more OH- ions ○ Ex: ■ Increasing pH (adding OH-) → Q > Ksp → decreases solubility of the salt → solubility is less in a basic environment...
Common-Ion Effect: when you try to dissolve the solid in a solution with either the cation or anion already present less solid will dissolve/more solid will be produced → the solubility of that salt is going to be less that it was in pure water ○ Q > Ksp...
For solids dissolving to form aqueous solutions ○ Ksp = solubility product constant = ■ Ksp value depends on ion concentration → more cations & anions = higher value ■ Solids not included in equilibrium expression...
A disturbance to a system at equilibrium causes Q to differ from K The reaction will “shift” to bring Q back into agreement with K Effects of Changes to a System You can change the position of equilibrium, but not the actual value of equilibrium (K) Pressure (only...
Le Chatelier’s Principle: if a system at equilibrium is changed, the position of the equilibrium will shift in the direction that tends to reduce that change
Type 1: Given initial concentrations and one equilibrium concentration Write balanced, dissolution equation → Set up ICE Table below ○ I: initial concentrations ○ C: Change in concentration ○ E: Equilibrium concentrations Solve for x If question...
The equilibrium constant of the reverse reaction is the reciprocal of the K value of the forward reaction ○ Ex: Forward reaction: (flip it) Reverse Reaction: When the equation for a reaction is multiplied by n, ○ Ex: mult. by factor of 2: When...
Use the magnitude of K to justify if a reaction favors the products or reactants at equilibrium K >1 products (forward reaction) are favored at equilibrium; more products than reactants ○ If K is VERY large, reaction goes essentially to completion ...
Equilibrium problems often include temperature → not needed in order to calculate K ○ K is a CONSTANT that only changes with temperature “Saturated solution” is at equilibrium
For the Equilibrium Constant Expression relates the concentrations of reactants and products once the reaction has reached equilibrium. ○ Equilibrium Constant Expression: ○ In questions, the equilibrium constant expression can be written as Kc, or...
Reactants decrease over time → forward reaction favored Products decrease over time → reverse reaction favored
Chemical equilibrium: when the rates of the forward reaction and the rates of the reverse reaction are equal (there is no change in the concentrations of reactants and products) Key Ideas: This does not mean the amount of product equals the amount of reactants ...
Hess’s Law: if you add chemical equations to get an overall equation, then you can also add the heat changes (ΔH) to get the overall heat change If two identical substances are on opposite sides of the arrow, they will cancel (reduce) If two identical substances are...
Standard State Standard enthalpy (ΔH⁰): the enthalpy change at standard conditions ○ ⁰ = recorded in standard state Standard State conditions: ○ For a gas: pressure is 1 atm ○ For a pure substance in a condensed state (liquid or solid) =...
It is the energy stored in a chemical bond → gives information about the strength of a bonding interaction (sigma = sum, D = bond) ○ Key Word: Bond enthalpy ○ If not sure what bond enthalpies to use, draw basic lewis...
Enthalpy (H) = heat ○ Is an extensive property and state function ○ E is the internal energy of the system, P is the pressure of the system, and V is the volume of the system ○ Units of ΔH = kJ ○ Key Word:...
→ endothermic (attractive forces are being broken; final answer [ΔH or q] = +); ← exothermic (attractive forces are forming; final answer [ΔH or q] = -) ○ Heat of fusion will be positive for melting and negative for freezing; heat of vaporization will be...
Heat capacity (C): heat absorbed per degree (J/C or J/K) ○ Extensive property: depend on amount of substance Specific heat capacity (cp): heat capacity per gram (J/C·g or J/K) ○ Amount of heat...
Temperature: average kinetic energy of a substance ○ Reflects random motions of particles ○ A change in temperature indicates an energy change Heat: involves the transfer of...
Endothermic Products have more energy than reactants ○ +∆𝐻 ○ Ex: decomposition reaction Forward reaction has higher activation energy than reverse Exothermic: Products have less...
Energy: the capacity to do work or to produce heat ○ J = SI unit for energy ■ kJ = 10^3 J Work: force acting over a distance ○ W = Potential Energy: due to position or composition (stored energy) → can be converted to work ...
Catalyst: chemical agent that speeds up a reaction without being consumed by the reaction → can be used over and over again ○ Do not affect the free energy/enthalpy of a reaction! ○ Reactions with a catalyst will typically require at least 2 steps...
The slowest (rate-determining) step in a mechanism will have the highest activation energy ○ On graph, will have the highest peak Number of peaks = number of elementary steps Intermediates are found in minimums of graph; the transition states are found in...
Determining Rate Law When Slow Step is Not First Write rate law for slow step For fast step: set the rate of the forward reaction (k₁) = rate of reverse reaction (k₋₁) Then solve for the [intermediate] Plug in the equation into the slow step
The rate of a reaction can be no faster than the slowest step We cannot use the coefficients from a balanced, overall equation to deter mine the orders of a reaction ○ Ex: We can use the coefficients from an elementary reaction determine the orders of a...
Activation energy: Activated Complex - Change in Reactants (peak - line) Transition state/Activated complex: bonds are partially formed (shown on curve’s peak) Activation energy of reverse reaction: Forward Activation Energy - | ∆𝐻 | ∆H/∆E (total energy change/energy...
Collision Model: the energy (for breaking bonds of reactants) comes from the kinetic energies possessed by the reacting molecules before the collision ○ Key idea: the rate of a reaction depends on the number of successful collisions and these collisions...
Reaction Mechanisms A chemical equation does not tell us how reactants become products ○ Simply a summary of the overall process Elementary steps: series of steps by which a chemical reaction occurs ○ Cancel out identical species on opposite sides...
First-Order Rate Law Order = 1 → changing the reactant concentration has an identical effect on the reaction rate (same factor) Rate Law = If a plot of ln[A] versus time is a straight line → reaction is first order Integrated First Order rate law: (on reference...
Initial Rate Method: the “instantaneous rate” just after the reaction beings; Usually the fastest ○ K = rate constant; m and n = rate orders Rate Constant (k): relates the rate of the reaction to the concentration of the reactants = slope ○ Value...
Spontaneous reactions: reactions that will happen but we cant tell when or how fast Kinetics: the study of the rates of a chemical reaction Can determine the coefficients of the chemical equation when given graph of concentration vs time by doing: ○ The...
Know that it is a redox reaction by a change in oxidation states Oxidation States Oxidation Numbers: signifies the number of charges an atom would have in a molecule or ionic compound if electrons were completely transferred Know which atom has been reduced/oxidized...
Arrhenius concept: acids produce H+ in solution, bases produce OH- ion (but what about NH3?) Bronsted-Lowry: An acid is a proton (H+) donor. A base is a proton acceptor Lewis Acids: electron-deficient molecules (+)...
Common Types of Chemical Reactions Precipitation Reactions: formation of a solid occurs Acid-Base Reactions: involves a transfer of H+ ions Justify: ○ Acid donates a proton & becomes its conjugate base ○ Base accepts a proton & becomes its...
Acid-Base Titrations Neutralization reaction: acid base reaction; produces salt and water ○ Neutralized: when just enough base is added to react exactly with the acid in a solution Titrant: solution of known concentration used in titration (in buret)...
Stoichiometry of Precipitation & Acid-Base Reactions Follow procedure when given molarity units
Physical vs Chemical Changes A physical change is a change in the form of a substance, not in its chemical composition = reversible ○ A physical change can be used to separate a mixture into pure compounds, but will not break compounds into elements ...
Write out equation and then balance it Number of molecules = number of moles (the coefficients) → always count # of particles
A representation of a chemical reaction→ must be balanced! ○ On AP exam, if coefficients are given can assume that the equation is balanced Balanced Formula/molecular equation: show all species participating in reaction ○ These equations indicate that...
The Beer-Lambert law relates the absorption of light by a solution to three variables according to the equation We can determine the concentration (molarity) of a sample by looking at the absorbance Factors Affecting Calculations Dilution (left water)→ measured...
Photoelectric Effect: the wavelength of the photon is related to the frequency of the radiation When a photon is absorbed or emitted by an atom or molecule, energy is increased or decreased by an amount equal to the energy of the photon Planck's Constant Planck’s...
Spectroscopy Applying different types of radiation to atoms and molecules can give info Energy lvls: UV > Visible > Infrared > Microwave Ultraviolet/visible radiation: transitions electrons from one energy lvl to another (higher) one Gives info about atomic...
“Like dissolves Like” (don’t say it in exam) → Water dissolves polar molecules (have dipole moment) and does not dissolve nonpolar molecules ○ polar–polar and nonpolar–nonpolar → are more attracted to each other than themselves → the heat of solution is...
Filtration Filtration can be used to separate the insoluble components of a heterogeneous mixture based on differences in particle size but NOT the components of two miscible liquids ...
Molarity (M): A.K.A Concentration Ex: A solution that is 1.0 molar (written as 1.0 M) contains 1.0 mole of solute per liter of solution. Note: brackets around something it means the “molarity of what is inside” Dilution: water is added to achieve the molarity desired...
Water: The Universal Solvent Water is a very versatile solvent because polar molecules are attracted to other polar molecules + its molecules form HB (adhesive) ○ (+) and (-) attraction Why are ionic compounds soluble in water? ○ When ionic compounds...
For real gases, the deviation from ideal behavior and predicted pressure is bcuz the particles of real gases have volume and intermolecular forces → PV does not equal nRT The gas which gas deviates the most from ideal behavior will be the one with the strongest IMF...
Gases consist of particles (atoms or molecules) that are in constant random motions Gas particles are constantly colliding with each other and the walls of their container There are no interactive forces (attraction or repulsion) between the particles of a gas...
A Gas (Review) Uniformly fills any container (have variable volume) Mixes spontaneously and completely with any other gas Exerts pressure on its surroundings Pressure Is equal to force/unit area Pressure equals the number of collisions with the particles and its...
The Three States of Matter Gas: molecules/atoms have enough energy to move freely ○ Particles so far apart from each other that intermolecular forces not considered ○ Indefinite shape and volume Liquid: strong intermolecular forces and molecular motions ○ Particles...
Introduction to Structures and Types of Solids Crystalline solids: have highly regular arrangement of their components (NaCl) Amorphous solids: have considerable disorder in their structures (glass) Lattice: represents the positions of the components in a crystalline...
Intramolecular vs Intermolecular Intramolecular bonding: what holds atoms together within the molecule ○ Covalent or ionic Intermolecular forces: forces between (rather than within) molecules Intermolecular Forces Weaker interactions that occur between...
VSEPR Model: Valence shell electron-pair repulsion → used to predict the geometries of covalent compound ○ States that structure of a molecule is principally determined by minimizing electron-pair repulsions between atoms ■ The lone and bonded...
Resonance Resonance: is used when more than one valid Lewis structure can be written for a molecule (can move a double bond between the same elements) ○ Actual electron structure of the molecule is an average of these resonance structures Equal...
Lewis Structure for Ions Rule: only the valence electrons are included → Metal cation won’t have any dots Lewis Structure for Molecules with Covalent Bonds How to Draw Lewis Structures Identify central atom → usually element that is drawn first and there is only one...
Metallic Solids Metallic solid: are held together by the strong forces of attraction between the positively charged metal ions and delocalized electrons (electrons not associated with a single atom or molecule) ○ Bonding is equal and nondirectional...
Ionic solids: stable substances held together by opposite charges (electrostatic attraction) Will not conduct electricity in solid form → only when ions are mobile (melted (molten) or dissolved) ○ In order to conduct electricity need charged particles...
Chemical Bonds Bonds: forces that hold groups of atoms together and make them act as one unit; attraction between the nucleus of one atom and the electron of another ○ Bonds occur so atoms can achieve noble gas electron configuration ○ As the...
Ionic Bonding Ionic Bonds Electrons are transferred from one atom to another creating ions Metal + nonmetal ○ Metals form cations (lose e- bcuz low IE) and nonmetals form anions (gain e- bcuz high IE) ○ Cations are attracted to anions; (+)...
An Introduction to the Periodic Table Column/Families/Groups Tell us how many valence electrons are in the outermost s and p shells Elements with similar properties are found in the same group Rows/Periods Tell us which shell the valence electrons are found; each row...
Electromagnetic Radiation (EMR) EMR: energy that exhibits wavelike behavior and travels thru space at the speed of light in a vacuum Ex: light from the sun, X-rays All EMR travel at speed of light Each form of EMR is only different in wavelength Photon: tiny particle...
Notes Reaction Stoichiometry: mass relationships between reactants and products in a chemical reaction Mole Ratio: conversion factor that relates amount in moles of two substances in chemical reaction Coefficients convey ratio of substances needed for the reaction to...
Mass Spectroscopy Why are atomic masses not whole numbers? Because they are weighted averages of isotopes Mass spectroscopy: study of the manner in which substances interact with electromagnetic radiation Isotopes: atoms with the same number of protons (same element)...