AP Chemistry updated +semester 2 : Nitya Marepally Period 5

enthalpy: internal energy

entropy: randomness of particles

spontaneity: when a reaction is thermodynamically favorable and doesn't need a forced reaction

Free energy: the ability of a system to do work

Hess's law: a way to calculate the change in entropy of a reaction

Free energy equation: relates the temperature, entropy and enthalpy of a reaction to the free energy

the change of entropy/free energy/enthalpy: change of products - change of reactants.

Gibbs Free Energy (delta G): The change in chemical potential of a system

Relationship between thermodynamics and equilibrium:

delta G = -RTln(K)
-The spontaneity and thermodynamic favorability of a reaction determines which direction a reaction will go from equilibrium

Integrated rate laws and determination: - If a reaction is 0 order then the graph of [A] vs time will be linear. The equation is [A]_t = -kt [A]_0

If a reaction is first order, time vs ln[A] will be linear. The equation is ln[A]_T = -kt + ln[A]. If it is second order, the graph of 1/[A] is linear. The equation is 1/[A]_t = kt + 1/[A]_0.

ln(k) = ln(A) - E_a/RT

Pseudo order rate laws are when the concentrations of all the other reactants are so high that the rate law is only dependent of the concentration of one reactant

Half-life using integrated rate laws: - for 0 order use t_1/2 = [A]_0 /2k .

for 1 order use half life = 0.693/k
-for 2 order use half life = 1/k[A]_0
The equation for first order is closest to true half life.

Relationship between kinetics and equilibrium: In equilibrium, K= [reactants]/[products], which can be converted to K1 [reactants] = K-1 [products] at equilibrium. If you divide K1 by K-1, that gives you [products]/[reactants] which, times k (rate constant) = the rate of the reaction.

Concentration of reactants' affect of rate is based on order of reaction. Increase in temperature, surface area, concentration, and pressure all cause the rate of the reaction to speed up because of more effective collisions.

A reaction is always spontaneous when delta H and S are negative and positive respectively. It is spontaneous when H and S are both positive only at high temperatures and spontaneous when H and S are both negative only at low temperatures.

Catalysts provide alternate pathway that requires less activation energy, therefore, a fewer number of effective collisions, so it causes the rate of reaction to speed up

A larger amount of product moles, changing from a solid to a liquid or gas, increase in temperature ,and dissociation all increase entropy.

Atomic radius: There are many methods of measuring the radius of an atom and all produce slightly different values. The Van der Waals is measures the non-bonding radius/London dispersion. The covalent radius measures the bonding. The atomic radius is an average radius of an atom based on measuring large numbers of elements and compounds. The atomic radius decreases across the period because the increased nuclear charge an electron experiences, stronger the attraction it will have for the nuclear. The stronger the attraction the valence electrons have for the nucleus, the closer their average distance will be to the nucleus. Moving across period increases effective nuclear charge on the valence. The atomic radius increases down a group because more energy levels are added and the pull on the valence electrons in the atom decreases, allowing it to expand.

Reaction to magnetic forces: Elements with one or more unpaired electrons are affected by a magnetic field, or paramagnetic. Elements with zero unpaired electrons are not affected by a magnetic field, or diamagnetic.

First ionization energy: The first ionization energy is the amount of energy required to remove one electron from the atom an element in its gaseous state.The strength of attraction is related to the most probable distance between the electrons and the nucleus. The farther away the electron is from the nucleus and the more shielding there is, the lesser amount of energy is required to remove the electron, Therefore, the first ionization energy decreases across a period and down a group.

electron affinity: Electron affinity is the measure of change in energy when a neutral atom gains an electron in the gaseous state.It is defined as exothermic (-) but can be endothermic (ex. some alkali earth metals and all noble gasses). This is because noble gasses already have a full shell, therefore, adding an electron would make the atom more unstable, similar to alkali earth metals, who already have a full s orbital, and would need to extend into p or d orbitals with one extra electron. If more energy is released, the electron affinity is higher.

Shielding: Electrons block the pole of the nucleus. Shielding only takes place in a multi electron system. Therefore hydrogen is irrelevant. Electrons in an atom are both attracted to the nucleus and repelled by other electrons. This causes the valence electrons to be shielded from the pull of the nucleus by he core electrons. Shielding prevents the valence electrons from experiencing the full strength of the nuclear charge.

Effective nuclear charge and penetration: Zeff is the net positive charge that is attracting a particular electron and is calculated by subtracting the number of non-valence electrons from the overall nuclear charge.The s orbital is the best at shielding/screening and then p, d, and f. Greater shielding causes increases the probability of penetration. The probability of finding electrons increase as the distance from the nucleus decreases.The better an outer electron is at penetrating the core electron cloud, the attraction it will feel for the nucleus. The degree of penetration is based on the orbital's radial distribution function.

Coulomb's law: This equation calculates the lattice energy in compounds. Lattice Energy = k(Q3 Q2)/r^2. Q3 and Q2 are the charges on the each of the ions in the compound, the r is distance between ions.

Bonding

Ideal Gases

All collisions are elastic

Particles have no volume

Molecules are not attracted to each other

particles are in constant, rapid, random motion

Kinetic energy

Average kinetic energy of gas particles depends on temperature, not identity of particle.

Gases at same temperature will have the same kinetic energy

Kinetic energy(joules) = 1/2 mv^2

Same kinetic energy and temperature does NOT mean same velocity

PV=nRT, D= MP/RT

Density at STP (273K and 1atm) = molar mass/22.42 L

Intermolecular attraction

strength of attraction between particles at that temperature determines its state

stronger attractions = higher boiling point for liquids and higher melting point for solids

Occur due to attractive forces between opposite charges

+ion to -ion -> ionic bonding

electronegativity tells polarity: +end of polar molecule to - end of polar molecule -> Dipole-dipole

particularly large electronegativity difference between H and NOF -> hydrogen bonding

Temporary polarity in the molecule due to unequal electron distribution (all halogens and covalent) -> London dispersion/Van der Waals

Larger charge=stronger attraction=closer together

More energy is required to break and intramolecular bond than intermolecular bond

Trends in strength of intermolecular attraction

stronger attraction=more energy to break

When boiling liquid, need enough energy to overcome all attractions between particles but not bonds itself

Boiling point occurs when vapor pressure=atmospheric pressure

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ACTUAL BONDS WILL ALWAYS BE STRONGER THAN IMFS

Dipole-dipole

polar molecules have permanent dipole

check VESPR

dipole moment must be present for induced dipole

LARGER MOLECULE=STRONGER IMFS

london dispersion

temporary seperation of charges

causes a temporary dipole

present in all substances

Induced dipole

magnitude depends on

polarizability/volume of electron cloud

Geometry/shape: more surface to surface contact=larger induced dipole

Ion-dipole

only in solutions

larger charge/smaller size=stronger attraction

ions attracted to dipole of polar molecules

strength of this attraction determines solubility

one of strongest imfs

Vapor pressure

the pressure of the vapor at equilibrium

all liquids have vapor pressure

vapor pressure depends on temperature: higher temp.=higher pressure

vapor pressure doesn't depend on outside pressure

endothermic

based on size of imfs in liquid

volatile liquid= higher vapor pressure

When pressure is in dynamic equilibrium with liquid it is vapor pressure

WEAKER ATTRACTIVE FORCES=HIGHER VAPOR PRESSURE=MORE VOLATILE LIQUID

Solutions

Solute= thing being dissolved

solvent= thing dissolving

mole fraction must add to 1 (mol/total mol)

Heat of solutions

amt heat energy absorbed is releasead when specific amt of solute dissolves in solvent

Solution forms when...

negative heat of solution+very exothermic

+heat of solution ONLY if entropy driven (G<0 / more disorder)

can be exo or endo

energetics

To make solution...

Overcome all attractions between solute particles ( delta H is endo)

Overcome some attraction in solvent particles (delta H is endo)

Form new attractions between solvent and solute (delta H exo)

delta H solution = H solute +H solvent +H mix

Does the solution form?...

Solvent-solute interaction=solvent -solvent/solute-solute = solution forms

Solvent-solute interaction<solvent -solvent/solute-solute = solution maybe forms based on whether energy difference is small enough and increase in entropy is large enough

Solvent-solute interaction>solvent -solvent/solute-solute = solution forms

Like dissolves like

Raoult's/ modified Raoult's law: Psolution = molfrac solvent * P solvent

Psolution = molfrac A Pa +molfracB Pb

Ideal solutions

liquid-liquid solutions that obey Raoult's law

Liquids for similar imfs=strong forces of attraction= lower vapor pressure

Negative deviation from Raoult's law (lower than predicted pressure)

Bonds formed = bonds broken / solvent-solvent attraction = solute-solute attraction / delta G=0

Solute and solvent are similar with strong forces of attraction

delta H of solution is LARGE and NEGATIVE

Positive deviation from Raoult's law (higher than predicted vapor pressure)

solute and solvent are not similar and only have weak forces of attraction

Still forms solution

particles easily escape solution and become vapor -> higher vapor pressure

delta H is SMALL and POSITIVE/NEGATIVE

solids tend to dissolve when...

gases tend to dissolve when...

heated

stirred

ground into small particles

cold

high pressure

Ionic: electrons taken/ lost

Metallic: Delocalized

Covalent; electrons shared

Resonance and Formal charge: most plausible structure= one with formal charge closest to 0

sigma bond

pi bond

Lattice energy steps used when forming ionic compounds

PES can be used to determine identity of atom

Resonance is weakess for localized electron model

Acids and Bases

Arrhenius model: based on how they react in rxn

Bronsted-Lowry model: acid proton donor, base proton acceptor

Titration used to find pH or capacity of buffer.

Use Henderson Hasselbach when solving with buffers

Ksp for solubility of substances

Use ICE table to solve

5% rule

Electrochem

Oxidation is loss, reduction is gain

In galvanic/Voltaic cell - is anode/ oxidation and + is cathode/ reduction

in electrolytic cell - is cathode and + is anode

forced reaction

spontaneous rxn

Nernst equation