Chem/Phys Flashcards
Exergonic Reaction
A reaction that releases energy and becomes more stable. In a potential energy graph, this is shown by a lower end in the final reaction than initially.
Exothermic Reaction
Releases heat.
37 degrees Celsius in Kelvin
310K
How do you analyze TLCs?
Consider the polarity of 1) the solvent, and 2) the stationary phase. Silica is a highly polar stationary phase, while toluene is a non polar solvent. Compounds that are similar in polarity to the stationary phase will interact well with it, by remaining close to the starting point on the TLC membrane, while compounds that interact well with the solvent will have more mobility, and travel a larger distance towards the stopping point.
How do you go about answering a question that gives you multiple torques in a question, and asked for rotational equilibrium?
Rotational equilibrium means the new torque should be 0. Given multiple torques, take into account directionality, separating torque that results in the system to rotate clockwise vs. counter-clockwise, then the sum (taking into account directionality) is net torque. A torque that is equal in magnitude and opposite in direction is needed to reach rotational equilibrium.
When given elements, and asked about color, what should you be thinking about?
We are thinking about absorption of visible light, which excited electrons. Elements with unfilled d orbitals will be more likely to excite electrons, and have electrons move to a higher d orbital.
Definition of boiling point
Boiling point is the temperature at which the vapor pressure of a liquid and surface pressure are equal. Things (such as a leak in the apparatus) that increase surface pressure, will increase boiling point of a compound.
Explain potential effects on a distillation experiment
In a distillation experiment, the separation of the two liquids takes place in the fractioning column, so if the fractioning column is shortened, the liquids would vaporize and condense fewer times. If the pressure is lowered inside the distillation apparatus, the boiling point of both liquids would decrease. Heating the distillation flask at a slower rate will improve the separation of the liquids.
How does distillation separate compounds?
During distillation, the compound with a lower boiling point will be distilled first. During the experiment, an ebulliator is added to introduce small bubble to break the surface tension to prevent superheating.
What is required in order for a hydrogen bond to form?
In order for a hydrogen bond to form, you need a H donor, which is typically a compound with a Hydrogen bond bound to an electronegative element, and a H acceptor, which is typically an electronegative atom.
What is molecular geometry based on?
Molecular geometry is solely based on valence electrons on the central atom.
What happens when a supersaturated system is swirled?
When a supersaturated system is swirled, excess solution will crystallize or precipitate.
How to determine aromaticity
1) Cyclic
2) Planar
3) Conjugated
4) Meets Huckel’s Rule: 4n + 2 sp2 hybridized is a whole number
What are non-conservative forces?
Forces that result in energy loss in a system such as air-resistance and friction.
Cyanohydrins
Result from a reaction between aldehyde and Cyanide
Thionyl Chloride (SOCl3)
A commonly used reagent to convert Carboxylic acids to acyl halides (more reactive since it’s an acyl halide)
Functional Groups Acidity
1) Carboxylic acids (most acidic)
2) Phenol (Resonance stabilized)
3) Alcohol
4) Amines (Common base is Ammonia)
What solvent is best for polysubstitutions?
Polar solvents
What solvent is best for mono substitutions?
Nonpolar solvents
Lactam
Cyclic Amide
Lactone
Cyclic carboxylic esters
What happens if you decrease pressure above a solid compound?
Decreasing pressure, decreases boiling point, so solid is more readily converted into a less dense phase in a temperature-dependent manner
What happens when you decrease pressure above a solid H20 compound?
Since ice is less dense than liquid water (rare characteristic of water), decreasing pressure, decreases boiling point, changing the solid phase into a gas since it can be more readily changed into a LESS dense phase.
What signals are downfield & deshielded in H-NMR?
A signal is downfield (farther away from 0) when it is adjacent to an electronegative group that withdraws (deshields) electron density
How does IR Spectroscopy work?
Molecules with a dipole moment, bend and stretch when they interact with Infrared radiation
Characteristic peak of O-H in IR Spec
Broad peak at 3100-3500
Characteristic peak of C=O
Sharp peak ~1700
Characteristic peak of C=C
Peak at 1600-1680
Characteristic peaks of triple bonds
~2100-2260
Characteristic peaks of N-H in IR Spec
Peak at 3300-3500
How does NMR work?
Analyzes how a molecule interacts with external magnetic field in relation to the spin of protons and neutrons
Parent peak (M+) on Mass Spec
The peak farthest to the right, tells you the mass of the molecular ion
Distillation
Technique used to separate liquids with different boiling points
Extraction
Technique used to separate a liquid or solid product from a solution
What is Rf in TLC?
Measure of the distance traveled by a compound in comparison to distance traveled by solvent front
What is the purpose of vacuum distillation?
Facilitates the separation of liquids with high boiling points by decreasing ambient pressure
Equation for standing wave in a pipe with one end open and one end closed
λ = 4L/n
Wavelength (λ), Length of pipe (L), and n (number of harmonic, odd only)
Equation for standing wave in a pipe open at both ends
λ = 2L/n
Evaporative cooling
When the liquid evaporates from the skin in “dry heat” to prevent overheating. Liquid does NOT evaporate as readily in humid environments.
Positive Enthalpy (H)
Endothermic reaction- requires heat input
Negative Enthalpy (H)
Exothermic reaction- releases heat as output
How do you calculate change in Enthalpy?
Delta H = H(product) - H(reactant)
Relative Stabilization Energy (RSE)
The more negative RSE is the more stabilizing the substituent is
What is Ka
Acid disassociation constant, or how readily an acid disassociates in water. This is equal to Keq in a disassociation reaction (forward), or Keq = 1/Ka when the reaction is in the reverse direction
What solvents are preferable for Hydrophobic AAs during dimerization?
For dimerization, where hydrophobic AAs are interacting with one another to fold properly, hydrophobic solvents are LEAST favorable because the hydrophobic AA residues would interact with the solvent
How to determine orbital hybridization?
Determine number of valence electrons on central atom, and how many bonds and lone pairs on central atom
Internal reflection
Occurs when ray of light travels from medium with higher index of refraction to medium with lower index of refraction
How do you calculate Gibbs free energy of a reaction that is coupled with another reaction?
Sum the change in Gibbs Free energy of the formation of that reaction with that of the reaction it is coupled with
What is Keq of a spontaneous reaction?
Keq > 1 for a G < 0 (spontaneous reaction)
LiAlH4
Strong reducing agent that reduces carboxylic acid derivatives to primary alcohols
H2 with Pd
Reduces alkenes to alkanes, as well as carboxylic acid derivatives to alcohols
Diatomic Nitrogen (N2)
An inert, non-reactive gas that is commonly used in the atmosphere when working with reagents that may react with O2 or other reactive gases.
pH > pKa
More basic solvent, and residues are in their deprotonated form
pH < pKa
More acidic solvent, so residues are in their protonated form
Torque
Torque = rFsin(θ )
Ways to increase torque
1) Increase Force
2) Increase r = distance from lever
3) Increase angle between force and lever so that it is as close to perpendicular as possible
Effective Nuclear Charge (Zeff)
The attractive force of the positively-charged nucleus on the atoms’s valence electrons. Increases from Left to Right as more protons are added, but decreases down a column, because more core electrons are shielding the valence electrons
Atomic size/ radius
It decreases from left to right, and increases down a column since there is less attractive force between the positively-charged nucleus and valence electrons allowing an atom to increase in size
Ionic radius
The radius of charged species. Positively charged ions are smaller in size than the uncharged atom, and negatively charged ions are larger in radius than uncharged atoms.
Formal Charge
FC = # of valence electrons - # of bonds - # lone electrons
Jones Reagent
KMnO4 and CrO3; strong oxidizing agents that can convert aldehyde to carboxylic acid
What happens to boiling point if you DECREASE vapor pressure?
Decreasing vapor pressure, would require more kinetic energy for the vapor pressure to equal atmospheric pressure, so boiling point would increase
Nitrate
[NO3] -
Sulfite
[SO3] 2-
Sulfate
[SO4] 2-
Hypochlorite
[ClO]-
Chlorite
[ClO2]-
Chlorate
[ClO3]-
Perchlorate
[ClO4]-
Carbonate
[CO3]2-
Bicarbonate
[HCO3]-
Phosphate
PO₄³⁻
Ammonium
NH₄⁺
Manganate
MnO₄²⁻
Permanganate
MnO₄⁻
Mutarotation
Interconversion between anomers of a compound
When does a particle feel force by a magnetic field?
Magnetic force = qvB, so a particle must have a velocity and charge to feel a force.
Which halogens make the best leaving groups in acyl halides?
The largest halogens (further down a column) make the best leaving groups
How to minimize power lost during transmission through power lines?
P = I^2R, so to minimize power lost we should minimize current (I)
What is the trend of current flowing through a circuit?
Current tends to travel through the path of least resistance (Ex: If a circuit has a branch with no resistors, the current will attempt to travel through it first)
Grignard Reaction
A reaction that results in a new carbon-carbon bond by using organomagnesium species (RMgX) like CH3MgBr
Speed of acid-base chemistry in a reaction
Faster than carbocation formation, since carbocations are unstable. However, acid-base chemistry such as a proton transfer typically occur at a faster rate
What do you do when given the energy of a photon as eV?
Convert it to Joules using the energy for 1eV given (1.6 x 10^-9)
Ferrous Ion
Lesser charge “ous” - Iron (II) cation
Ferric Ion
Greater charge “ic” - Iron (III) cation
Higher Ka value
More acidic, since K is the ratio of products to reactants, a larger number implies that the acid dissociates completely in water
Large pKa
pKa = -log(Ka), so higher pKa is weaker acid
How to increase the acidity of a compound?
Resonance stabilization and MORE electron withdrawing groups closer to the acidic functional group
What do similar λmax of compounds in UV/Vis spec indicate?
UV/Vis uses light waves to determine the combination of groups of a compound based on light absorbance and reflectance. Similar λmax indicates similar chromophoric groups between compounds
When does a solution with a transition metal ion appear colorless?
When the transition metal has a full d orbital. The unfilled d orbital allows for excitation of electrons through absorbance of visible light that we see as color
How do you calculate the concentration of titrated solution?
When given the volumes of titrant and titrated solution, and the concentration of the titrant at equivalence point, use M1V1 = M2V2
Isoelectric Point of an AA
When the net charge of the amino acid is 0. In a neutral amino acid, usually when the Carboxylic acid is de-protonated and amine group is protonated
Mechanical Advantage
MA = Force(input)/ Force(Output)
W(input) = W(output)
Force(input)d = Force(output)d
Rearrange to get Force(input)/Force(output)
What happens when CO2 undergoes hydrolysis in water?
CO2 forms carbonic acid (H2CO3) a weak acid that gives water a pH less than 7
When is a negative value for pH acceptable?
When the concentration of hydronium ion (H+) is greater than 1M since
pH = -log[H+] = -log[10^1] = -1
Continuity Equation
A1V1 = A2V2, where fluid velocity and cross-sectional area are inversely proportional
Relationship between velocity and pressure
Inversely proportional
Partial Pressure
Partial Pressure = X(mole ratio of gas)*P(total pressure in container)
Temperature vs. relative humidity
At decreasing (colder) temperatures, relative humidity declines because percentage of water vapor declines
Volume that one mole of ideal gas occupies at STP
22.4L
Which phase changes are considered exothermic?
Changes from gas to liquid to solid
% Dissociation of an Acid
% dissociation = [H+]/[HA] * 100%
What makes Glycogen better as a storage molecule than amylopectin?
More alpha-1,6 glycosidic bonds making it more densely packed
Ammeter
Measure current
Ohmmeter
Measures resistance
Voltmeter
Measures potential
Direction of electric field lines
Move away from positive ions
What is the function of a salt bridge in a galvanic cell?
Electrons would flow from anode to cathode in an effort to reduce. After only a short time, however, the cathode half-cell would become highly negative in comparison to the anode half-cell. As electrons would now be traveling against their charge gradient, the process would grind to a premature halt. On the other hand, when a salt bridge is present to connect the two solutions, otherwise uninvolved ions can move to neutralize this charge difference. In this case, one sulfate ion will move to the right for every two electrons that move to the left.
What happens to density at higher altitudes?
Density and pressure decrease at higher altitudes
Relationship between boiling point and altitude
Since atmospheric pressure decreases at higher altitudes, boiling point decreases as well
Compressibility of gases’ effect on their density
Since gases are compressible, they have changing densities. This is a main reason for why studying buoyancy in gases is more complex than liquids
Solubility Product (Ksp)
A constant that measures the extent an ionic compound is soluble/ dissolves in water. Higher Ksp, higher solubility. Temperature and pressure changes impact Ksp
What changes when a wave travels through a different medium?
The speed or velocity at which the wave is traveling changes in different medium, and wavelength changes to maintain a relationship between speed and frequency
Glycerol Structure
Three CH groups bound to 3 OH groups, so can form 3 hydrogen bonds
Hydrofluoric Acid
A WEAK acid that does NOT completely dissociate in water
Relationship between vapor pressure & boiling point
Inverse relationship: compound with the highest boiling point has the LOWEST vapor pressure. It takes MORE heat to equalize vapor pressure to atmospheric pressure
Alpha Decay
Result in emission of an alpha particle (which consists of 2 protons & 2 neutrons)
The Two Types of Beta Decay
1) Beta-minus decay: neutron converted to proton and electron emitted
2) Beta-Plus decay: proton converted to neutron and positron emitted
Daughter nuclei of an alpha decay
Parent nucleus decreases in atomic number by 2 and atomic mass by 4
Daughter nuclei of Beta-minus decay
Atomic number increases by 1 and atomic mass stays the same
Daughter nuclei of Beta-plus decay
Atomic number goes down by 1 and atomic mass stays the same
Gamma Decay
The parent nucleus emits a gamma photon, resulting in the nucleus to go from a high energy state to a lower energy state but element, atomic mass, and number remain the same
Molality
moles of solute/ kilograms of solvent
Freezing point depression
ΔTb = Kfmi
Kf: freezing point depression constant
m: molality
i: van’t hoff factor (the number of components solute dissociates to)
Structure of Phosphatides
Phospholipids that are a major component of cell membrane; amphipathic with a nitrogenous end
What reactions favor thermodynamic control?
The reactions that have lower reaction times, more stable product (lower free energy), and usually reversible
What reactions favor kinetic control?
The reactions with the lowest activation energy (will occur faster), and irreversible
What is the reduction potential (Ecell) of a Galvanic cell?
Galvanic cells or voltaic cells always undergo a spontaneous reaction, so they have a POSITIVE Ecell
Relationship between Pressure & velocity in fluid systems
Inversely proportional; as velocity increases, pressure decreases to maintain energy balance
Relationship between area & velocity
Inversely proportional; as area increases, velocity decreases
How do you calculate the power of a lens
Equal to 1/f, so to calculate power, use the thin lens equation 1/f = 1/di + 1/do. Power of a lens is measured in diopters (m-1)
Anode vs. Cathode in Galvanic Cell
Anode (Negative, lower potential) and Cathode (Positive, higher potential)
Anode vs. Cathode in Electrolytic Cell
Anode (Positive, higher energy potential) & Cathode (Negative, lower energy potential)
What does ester hydrolysis require?
Strong acid such as H2SO4
Sublimation
Solid to gas phase change
Deposition
Gas to solid phase change
When to use Simple Distillation?
When the two compounds have boiling points <150 and are >25 degrees apart
When to use Fractional Distillation?
When the two compounds have boiling points <150 and are <25 degrees apart (smaller difference)
When to use Vacuum Distillation?
When the two compounds have high boiling points >150
Trend for increasing reducing agent strength in the periodic table
Reducing agents donate electrons, so reducing agent strength increases down a row as electronegativity decreases
SI unit for Coulomb (C)
Think of the equation for current (I) = Q (charge) / t (Time) so Amperes/ seconds
Lorentz Force
The force acting on a charge q entering a magnetic field of strength B at a velocity v (F = qvBsin(theta))
Resistance of a wire
R = resisitivity*Length/Cross-sectional Area
Color Wheel
What can Mass Spec detect?
Cations ONLY!
Electric force between two charges
kq1q2/r^2
Grignard Reaction
A carbon-carbon bond forming reaction that can convert ketones and aldehydes into alcohols when reacted with organometallic reagents
Hydrostatic Pressure Equation
P = densitygravitational accelerationheight
Single-Slit diffraction Pattern Equation
Sine(theta) = m*wavelength/width, where m = order of the minimum
