CHEMISTRY COMMUNITY

Patrick Cai 1L

The maximum work done is related to the formula standard free energy = n*F*E_cell.

Patrick Cai 1L

Pseudo-first order is when you have a rate law with some number of reactants, such that we make all except for 1 reactant constant (usually by making them in large excess so that any reactant used in reaction is negligible) and manipulate the reaction from there.

Patrick Cai 1L

Standard cell potential is defined as cathode minus anode by convention.

Patrick Cai 1L

Typically, we can approximate and use the ideal gas law wherever there is a simple atomic or diatomic gas at STP like that of helium and nitrogen; these are the most like point-particles.

Patrick Cai 1L

Typically, we can determine which step to be the slow step by first looking at experimental analysis and roughly determining what the rate is proportional to. It is from this point that we have to "guess" the elementary steps and identify a step that has reactants that are found in our exp...

Patrick Cai 1L

It was through experimental verification that we were able to tell over a given period of time, now called a radioactive substance's half life, that half of the substance would decay away; this fits within our model of a first order process.

Patrick Cai 1L

The units of the rate law vary with the order of the reaction, with the units of the general differential rate law given as moles/second ([change in concentration]/[change in time]).

Patrick Cai 1L

Metals pack together in lattices that have delocalized electrons amongst positively charged nuclei, resembling a "sea of electrons". This phenomenon allows for conductance of electrons and thus current.

Patrick Cai 1L

Typically, if only considering entropy of a reaction, if delta S is positive, then the reaction is considered spontaneous. However, there are more cases where temperature and enthalpy would need to be considered (Gibbs free energy equation).

Patrick Cai 1L

Common oxidation states to note are that the alkali metals are typically +1, alkali earth metals are typically +2, oxygen is typically -2 (except for in peroxides, which would be -1), hydrogen is typically +1, fluorine is typically -1, and chlorine is typically -1.

Patrick Cai 1L

This is just the given convention, because of how we define cell diagrams with anodes on the left and cathodes on the right. Further discussion would result in a physical, rather than chemical, explanation of current and electron flow.

Patrick Cai 1L

Entropy is proportional to the amount of possible microstates possible, and when a liquid goes to the gaseous phase, it has more potential states to occupy.

Patrick Cai 1L

Basically treat n as how you have treated it thus far with balanced chemical reactions, now just also being mindful of Faraday's constant.

Patrick Cai 1L

Most likely we would be only need to worry about batteries in the upcoming test but still knowing how to balance redox reactions would be good in general, like in the case of acid/base reactions.

Patrick Cai 1L

The anode is considered to be your electron source and the cathode is considered to be your electron reservoir.

Patrick Cai 1L

Gradually, there will become an excess of ions built up on either side of the battery cell, which will impede current flow and stop the reaction.

Patrick Cai 1L

There are two other cases where temperature has to be considered. If enthalpy is positive but entropy is also positive, at high temperatures the reaction would have a negative change in free energy and is spontaneous; if enthalpy is negative but entropy is also negative, at low temperatures the reac...

Patrick Cai 1L

For the graph, the point of lowest energy is where the reaction reaches equilibrium. Any other energy value will spontaneously move towards that lowest energy state and once equilibrium has been reached energy has to be inputted for it proceed. So your statement is correct, I believe.

Patrick Cai 1L

Everything in the syllabus prior to 4J, or entropy, will be covered. I believe that Gibbs free energy will not be be mentioned on the midterm.

Patrick Cai 1L

Some examples of intensive and extensive properties include density, which is a value independent of how much material you have, and mass, which is scales with the more substance you have, respectively.

Patrick Cai 1L

Reversible can be thought of as if the system and surroundings are at equilibrium, where any change in volume can be seen as a infinitesimally close to the original thermodynamic state; irreversible tends towards one direction and no small change can restore initial conditions.

Patrick Cai 1L

Ideal conditions usually implies that you are working with a monoatomic gas particles that elastically collide and thus can be modeled with the ideal gas law.

Patrick Cai 1L

Buffers are typically a solution containing a weak acid and its conjugate base or a weak base and its conjugate acid. Their overall effect, when subjugated to the introduction of either a strong acid or strong acid, is to lessen the degree by which the pH of the solution is affected. For instance, i...

Patrick Cai 1L

For the most part, we work with closed systems since isolated systems are not able to transfer energy or heat and open systems have non-constant variables of pressure, heat, etc.

Patrick Cai 1L

Essentially, if given the heat required to do so and the moles of substance analyzed. However, this may be different if other values are given.

Patrick Cai 1L

The units of enthalpy are typically (energy)/(moles), usually either Joules/mole or kiloJoules/mole.

Patrick Cai 1L

L*atm is equivalent to volume times pressure, giving us the fundamental SI units meters 3 * Newtons * meters -2 , equivalent to a newton*meter, or a Joule (W = -P \Delta V). In the case of thermodynamic systems, the questions would have units that would indicate towards what the final answer should ...

Patrick Cai 1L

Cells in this case would be seen exchanging molecules of CO₂ and O₂ while also having freely exchanging energy, making it an open system.

Patrick Cai 1L

Residual entropy is mostly considered in situations where all types of entropy is removed, such as the case of cooling molecules to almost 0 K. Under these conditions, the particles are considered motionless and thus we ignore aspects like entropy associated with gaseous phase particles, etc.

Patrick Cai 1L

A good equation mentioned today in lecture for calculating the number of possible degenerate state was the formula $W = 2^n$ , useful to determining all possible microstates of $n$ different and separate particles.

Patrick Cai 1L

These equations are theoretically derived as shown during lecture, typically involving work (which is equivalent to the negative integral of volume times pressure) and enthalpy (related the internal energy of the system) with assumptions of an idealized reversible thermodynamic system.

Patrick Cai 1L

Typically, the distinction between the object of interest and surroundings is the reaction vessel where the pertinent reaction is occurring and the rest of the universe. There are also cases where there are arbitrary boundaries made to distinguish the system from the rest of the universe, used more ...

Patrick Cai 1L

The units of Celsius and Kelvin should be interchangeable in this case, they are the same unit just shifted relative to each other.

Patrick Cai 1L

If needed, say there is a gaseous phase reactant or product in the system, the question would typically make a note to say either pressure or temperature is constant.

Patrick Cai 1L

Yes, steam at 100 degrees Celsius first undergoes a phase change from gas to liquid while remaining at the same temperature, releasing heat via condensation. Now, you are left with water at 100 Celsius which releases energy as same as the sample that started off as water at 100 degrees Celsius. This...

Patrick Cai 1L

In this question, the entire system is consisting of both the copper pot and water inside the copper. You must treat heat flow going to the copper pot, as it also changes in temperature as does the water inside.

Patrick Cai 1L

Protonation is the process of losing a proton, making a solution more acidic; deprotonation is the converse process. The process of determining protonation would be [conjugate base concentration]/[initial acid concentration]*100%, while deprotonation is [conjugate acid concentration]/[initial base c...

Patrick Cai 1L

For most intents, I think we will not be using such cases of superacids, as these are rather rare anomalies as compared to the scope of Chem 14B.

Patrick Cai 1L

The reason for this sig fig difference in calculations related to either pH or pOH can be seen on the Chem 14B website, under the link labeled "Everything you want to know about Significant Figures". Here, the concept of how floating point number is made is shown with respect to the mantis...

Patrick Cai 1L

As mentioned before, temperature is the only parameter that affects the equilibrium constant; this occurs as a result of how temperature actually affects the internal energy of the system, shifting the potential and kinetic energies of involved reactants and products.

Patrick Cai 1L

The specific process by which this happens was discussed in class today by Dr. Lavelle, autoprotolysis. Water (H₂O) occasionally, and spontaneously, pronates other water molecules, thus forming hydronium (H₃O⁺) and hydroxide (OH^-) ions.

Patrick Cai 1L

Yes, this implies that the reaction will need some defined period of time to reach dynamic equilibrium.

Patrick Cai 1L

If a reaction is given with reactants and products solely in the gas phase, we would use K_p and use partial pressures derived from concentrations and the ideal gas law. Otherwise, K_c would be used with the concentrations involved.

Patrick Cai 1L

The difference between strong and weak acids/bases is dependent on their dissociation of either hydrogen or hydroxide ions, respectively. Strong acids typically have anions with a high degree of electronegativity, allowing for their hydrogen ions to be loosely bound and prone to disassociate. Strong...

Patrick Cai 1L

Aqua- is used where there is water molecules inside the coordination sphere. For instance, [Cr(NH₃)₃(H₂O)₃]Cl₃ is triamminetriaquachromium(III) chloride.

Patrick Cai 1L

Hemoglobin is made from four myoglobin-like subunits that come together via their quaternary structure. The way these four proteins come together have no bearing on the heme group, which binds with the oxygen.

Patrick Cai 1L

VSEPR does not have methods to find the exact bond angle magnitude (this is determined experimentally), it can tell you the shape and range of what the bond angle could be. Therefore, for the test, you would be only able to write down <120 degrees.

Patrick Cai 1L

If HCl is not specified as aqueous, it is in its solid, powdered form, where it is not considered an acid.

Patrick Cai 1L

Typically chelating ligands have multiple sites that allow for cations to bind, therefore allowing for repetition and stronger binding.

Patrick Cai 1L

The first molecule possesses iodine atoms, which are substantially larger than the fluorine atoms found in the second molecule. With a larger atomic number, iodine has more electrons and a larger electron cloud. Iodine, therefore, has a larger polarizability value than fluorine and forces a group of...

Patrick Cai 1L

To fully understand the polarity of the CIF 3 molecule, we would have to realize the asymmetric distribution of atoms around the central carbon, as well as the differences in dipole moment noted between the C-I bond and the C-F bonds. Combining these two aspects, there is a net dipole in the directi...

Patrick Cai 1L

VSEPR integrates the lone pairs, and different bond types to give more information than a Lewis structure would about the 3D configuration of a molecule.

Patrick Cai 1L

This Lewis structure does not reflect the 3D structure of CH 2 Cl 2 , which is tetrahedral. With this arrangement, no matter what, at least two corners of the tetrahedron has chlorine atoms. This, along with the difference in electronegativity of chlorine and carbon, produces a net nonzero dipole mo...

Patrick Cai 1L

Delocalized pi bonding is essentially the sharing of a pi bond over more than two nuclei. This can be prominently be seen with benzene, which shares 3 pi bonds over 6 carbon nuclei and contributes to the ring of electron cloud density characteristic of benzene.

Patrick Cai 1L

Polar molecules have one thing in common: a net nonzero dipole moment. To determine the dipole moment, one must consider the spatial distribution of the atoms and electron clouds, as well as the differences in electronegativity between the bonded atoms. For instance, in the case of H 2 O, both the e...

Patrick Cai 1L

Magnitude is meant as the strength of the dipole, usually given in units of debyes.

Patrick Cai 1L

Yes, but for ionic lewis structures, there are brackets around both the anion and cation with charge displayed to indicate that it is an ionic compound.

Patrick Cai 1L

Lone pairs are considered separate from one another, this is apparent with the sp³ hybridization of H₂O, which has two lone pairs and two bonds.

Patrick Cai 1L

Butanol is a somewhat polar molecule, as evident by the presence of its alcohol functional group (-OH), whereas diethyl ether is a non-polar molecule. The stronger intermolecular forces that come along with butanol as a result of its polar nature make it have a higher melting point than diethyl ether.

Patrick Cai 1L

In most cases, hybridized orbitals occur as the optimal, lowest energy state configuration a molecule can have; however, some examples exist of molecules whose un-hybridized orbitals are at a lower energy state than having potentially hybridized orbitals (H₂S).

Patrick Cai 1L

Formal charge is determined by the formula FC = [# of valence electrons on atom] – [non-bonded electrons + number of bonds]; this is useful in determining whether or not a molecule is stable. Partial charge is a notation used to indicate that a molecule has an an asymmetrical distribution of charge ...

Patrick Cai 1L

Ionic compounds still have London dispersion forces occurring, since the presence of a polarizable electron cloud allows for it. However, the primary intermolecular force present will be that ionic attraction.

Patrick Cai 1L

Polar compounds typically have significant dipole moments and dissolve in the most ubiquitous polar solvent, water. They tend to also have higher melting and boiling points than nonpolar compounds with molecular weights similar to them. Nonpolar compounds lack dipole moments and thus don't dissolve ...

Patrick Cai 1L

Hydrogen bonding is the result of an especially polar bond occurring between the highly electronegative atoms of the upper right section of the periodic table (nitrogen, oxygen, and fluorine) and hydrogen. For most compounds that contain hydrogen, for instance hydrocarbons, hydrogen bonding is not p...

Patrick Cai 1L

Sigma bonds are the first type of bond to form (single bonds) in chemical reactions, of which orbitals bond end-to-end and allow for rotation along the internuclear axis. Pi bonds are the second type of bond to form (double and triple bonds) in chemical reactions, of which orbitals bond above or bel...

Patrick Cai 1L

VESPR shapes are formed more specifically to maximize repulsion between the regions of electron cloud density.

Patrick Cai 1L

H₂O is not linear because in addition to its 2 bonding pair electrons, it also has 2 lone pair electrons that distort the shape of the atom to resemble an exaggerated tetrahedron. This explains the bent shape of H₂O and the presence of a 104.5 degree H-O-H bond angle.

Patrick Cai 1L

Dipole is defined as the following: "a pair of equal and oppositely charged or magnetized poles separated by a distance." Induced dipole occurs as a result of the polarizability of an electron cloud of a molecule. When an electrically neutral molecule is in close proximity of an ion, the c...

Patrick Cai 1L

Typically, molecules with stronger intermolecular forces tend to have higher melting and boiling points, with hydrogen bonding strength > dipole-dipole interaction > van der Waals interaction.

Patrick Cai 1L

The general trend for dispersion forces is indeed related to the number of electrons tied to the atom or molecule. Therefore for larger atoms or molecules, the more electrons they have and the greater amount of dispersion forces present.

Patrick Cai 1L

Basically yes. A formula unit indicates the lowest whole number ratio of ions in an ionic compound, as contrasted to molecules, which are composed of two or more elements covalently bonded.

Patrick Cai 1L

The Z-effective of Ca 2+ is greater than that of Na+, which is to say the electrostatic attraction between the remaining electrons of Ca 2+ and protons of the nucleus eclipses the electrostatic interaction measured in Na+.

Patrick Cai 1L

Given that blackbody radiation was observed as a macroscopic effect, the generalizations produced by classic blackbody radiation theory holds true for classic mechanics. However, if we were to consider the quantized nature of matter, increasingly specific analyses of blackbody radiation fails at the...

Patrick Cai 1L

Radical compounds form in the context of redox reactions, in which a certain chemical species is given an unpaired electron. A prominent example (and one mentioned in class) is the methyl radical, which forms from the incomplete combustion of ethane.

Patrick Cai 1L

The Lewis structure version that has the more optimized combination of atoms with formal changes equal to 0 or as closest to 0 would be the more stable Lewis structure.

Patrick Cai 1L

An example of an element being bonded with more than 8 valence electrons shared is phosphorus in the compound phosphorus pentachloride (PCl₅), which forms an expanded octet to accommodate this change.

Patrick Cai 1L

Light slows down when in any medium with some amount of matter (water, gas, etc.) because light particles would interact with atoms, get re-emitted, and take a longer period of time to traverse the same distance it would normally travel in a vacuum. For calculating the speed of light through other m...

Patrick Cai 1L

Ionization energy is the energy required to remove an electron from any atom to turn it into an ion. Electronegativity is a measure of how strongly an atom attracts electrons.

Patrick Cai 1L

It is a good rule-of-thumb to assume most atoms of the p-block elements want a full octet, or eight electrons in their valence shell. There are exceptions to this eight electron rule, including hydrogen, which tends have 2 electrons in its valence shell once full.

Patrick Cai 1L

Photons are the elementary particle that is responsible for carrying the electromagnetic force and manifests in electromagnetic radiation. Photons exhibit wave-particle duality, so light is carried by photons which have wave-like and particle-like tendencies.

Patrick Cai 1L

n: the energy level (goes from n = 0,1,2,...) l: the subshell (goes from l = n-1, n-2,...0) m l : the orbital (goes from m l = l, l-1,...-l+1,-1) m s : one of the two electrons that may be within an orbital (either +1/2 or -1/2) First 3 quantum numbers, when expressed as parameters of the wave funct...

Patrick Cai 1L

From the classic double slit diffraction experiment carried out using an electron beam, it was proven that individual electrons would make contact at singular points on the other side (demonstrating a particle-like nature) but given sufficient time and electrons passing through, the resulting patter...

Patrick Cai 1L

The answer is C: incoming, large. It is because the energy that is exciting the electron and causing it to be ejected is coming from the incident (incoming) light from some given light source, with photons of a given energy greater than the work function to actually eject the electrons.

Patrick Cai 1L

Silver is among the elements (other examples include copper and gold) with special electron configurations, where it is more energetically stable to have a full d-shell rather than a full s-shell. This is why silver's electron configuration is [Kr] 4d^10 5s^1 rather than [Kr] 4d^9 5s^2.

Patrick Cai 1L

Prof. Lavelle has made measurements of light using the wavelength of light, for instance when he mentioned that the wavelengths of violet and red light are 400 and 700 nm, respectively. Wavelength is typically used to determine the color of light.

Patrick Cai 1L

When in doubt, you can attempt to use dimensional analysis to double-check that you are using the right units. For instance, if you are given Planck's constant's but you forgot the units of it, you can use de Broglie's equation to back-solve for what units Planck's constant is.

Patrick Cai 1L

The idea of a free radical is not necessarily restricted around even or odd number of valence electrons it has; rather it is dependent on an atom having a "free" electron that is highly unstable and this electron seeks to form a bond by taking an electron from another atom/molecule. Diamag...

Patrick Cai 1L

Honestly there is no easy way to go about this, the best way is to brute force memorization of the set of prefixes. Maybe use flashcards?

Patrick Cai 1L

Theoretical is the value that you obtain from doing stoichiometric calculations and obtaining a number for the maximum possible amount of product. Actual is the value you obtain experimentally, as a result of doing the experiment in a real world setting. In such a situation, the reaction being analy...

Patrick Cai 1L

The way that microwaves work to heat up food is that it interacts in a special way with water. The resonance frequency of water is within the microwave range, so when microwaves are applied to a sample containing water, the water molecules begin to vibrate and produce heat on the macroscopic scale. ...

Patrick Cai 1L

The note is making the statement that there is no need to start from averaging the atomic weights of the two predominant isotopes of copper, then multiplying by Avogadro's constant to get molar mass. Instead it is suggesting that you can just take the molar masses of copper-63 and copper-65 and take...

Patrick Cai 1L

Yea, for this question it asks for the mass percentage composition which is basically asking for the mass percentages of all elements present in l-carnitine. It can be easy to miss that one word that gives you the entire question, I did that in my first reading of the question too.

Patrick Cai 1L

For doing stoichiometric calculations, typically reactants/products with a coefficient of one are not written with the number 1, as it is implied by convention there is one mole of that reactant/product. I personally have not seen the number 1 written down by any previous chemistry teacher.

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