CHEMISTRY COMMUNITY

Mackenzie Stockton 2H

Because E = E* - (RT/Fn)lnQ, the voltage of a cell depends on concentration

Mackenzie Stockton 2H

sea water leads to rust formation because of the high concentration of salt, which dissolves to create an electrolyte rich solution , which transfer electrons to form rust

Mackenzie Stockton 2H

rechargeable batteries are unique in that they only depend on reversible reactions

Mackenzie Stockton 2H

pH meter measures the hydronium concentration, which tells us about pH since pH=-log(H30+)

Mackenzie Stockton 2H

If the concentrations were equal, the E0 cell= 0 (system at equilibrium)

Mackenzie Stockton 2H

to find standard reaction enthalpy,

find the total standard enthalpy of formation of the products (summation) - standard enthalpy of formation of reactants

Mackenzie Stockton 2H

I believe that the higher the density, the greater the capacity.

hope this helps!

Mackenzie Stockton 2H

to calculate entropy, use

delta G = delta H - T delta S

hope this helps!

Mackenzie Stockton 2H

For 25C (298K), use the log equation.

Mackenzie Stockton 2H

When using standard reduction potentials, it is cathode-anode

Mackenzie Stockton 2H

Ecell= cell potential
Eocell= standard cell potential. this means it is the cell potential measured at standard conditions (1 atm, 25 deg C/298K)

Mackenzie Stockton 2H

As others have provided, the link is very helpful. It cleared a lot of things up for me.

Also, in general atoms have oxidation numbers that match their charges that we have worked with in 14a and 14b

Mackenzie Stockton 2H

Look at the coefficient when balancing the overall charge on each side of the reaction.

Mackenzie Stockton 2H

The botlzman equation is used to calculate entropy.

Second law of thermo- for a process to be spontaneous, delta (entropy of the universe) > 0

Mackenzie Stockton 2H

The cell can do work whenever Ecell > 0

Mackenzie Stockton 2H

I asked a TA about this an they are the same equation. In one of them the - sign is factored out, but you get the same answer.

Mackenzie Stockton 2H

say X = ln (K)

e^X = K

take e to the power of the thing on the other side of the equal sign

Mackenzie Stockton 2H

no, I am memorizing it because I feel like it will come up on the exam

Mackenzie Stockton 2H

the way I think of it is that gases are more "loose" and have more motion- molecules aren't held as tightly, so more motion means more entropy (disorder).

Mackenzie Stockton 2H

I believe they are given in the equation sheet so we do not have to memorize them

Mackenzie Stockton 2H

this makes sense because entropy does not decrease spontaneously for any system. For something to happen spontaneously (by itself), entropy will increase

Mackenzie Stockton 2H

the Gibbs free energy change of a spontaneous reaction will be negative

g=h-t(delta)S

Mackenzie Stockton 2H

Isolated system because the universe cannot gain or lose energy. Kinda hard to wrap your head around...

Mackenzie Stockton 2H

entropy (S) ---> S= KblnW1W2

its helpful to think of entropy as a measure of the disorder of a system

Mackenzie Stockton 2H

Closed system means matter is not exchanged between the system and surroundings, so Volume cant be exchanged.

Mackenzie Stockton 2H

The change in internal energy remains constant and is essentially 0.

Mackenzie Stockton 2H

Path A- reversible
use w=-nRTln(V2/V1), first find n= PV/RT

path b- constant pressure, irreversible
use w=PdeltaV

Mackenzie Stockton 2H

Hi , the integral, from what I remember, is the area under a curve. This is used to represent the summation of many values, in this case the summation of many values of work over a period that we change the volume. Summing up these little steps for a system thats reversible (at equilibrium) will yie...

Mackenzie Stockton 2H

Because work is dependent on distance, (w=Fd), and state functions do not depend on the path taken

Mackenzie Stockton 2H

When the system expands volume, it is using energy, so it loses this energy to the surroundings (the - sign is meant to show how the system is losing energy by doing work). Since delta V is positive, W ends up being negative

Mackenzie Stockton 2H

System in equilibrium- reversible process- this is achieved in a series of small steps (infinitely long) for an infinite amount of time. This is more efficient because there is more work achieved than a "fast process" Fast process- system not at equilibrium (like when the moles of gas on t...

Mackenzie Stockton 2H

A change in 5 degrees C is the same as a change in 5 Kelvins. If you are using the equation with delta T, since this is a change in temperature, and kelvin and celsius change on the same scale, you do not need to convert

Mackenzie Stockton 2H

molar heat capacity is the amount of heat required to raise one mole of a substance by 1 degree Celsius. I assume these will be used on the textbook problems :)

Mackenzie Stockton 2H

In general, if the first row has a "0", then the second row will be adding x or 2x, etc But for a more formal look at this, you should compare Q and K. If Q < K, then the reaction needs more products, and will proceed to the right. So the products will have a +x or +2x etc while the produc...

Mackenzie Stockton 2H

Catie Donohue 2K wrote:So just to clarify what's already been said, catalysts control the speed of endothermic and exothermic reactions, but do not affect the change in enthalpy of the reaction?

Yes, that is correct :)

Mackenzie Stockton 2H

Standard states are at 1 atm and 25 degrees Celsius. When trying to find the standard state of a molecule, if you cant look it up, I think we should just go with what we have seen in this class, like in previous problems in example. For example, N2 would be N2(g) and H would be H2(g), as these are w...

Mackenzie Stockton 2H

Hello! I think the ones he mentioned in class were He(g), Ar(g), N2(g), O2(g), F2(g), H2(g), Cl2(g), B2(l), I2(s), most stable form of carbon is graphite. I think in general we should just do what "feels right" or what we have seen before when trying to figure out the standard state in a p...

Mackenzie Stockton 2H

Catalyst speed up a chemical reaction by lowering the activation energy.

Enthalpy is a state property, so it does not depend on the path taken. Therefore, lowering the activate energy will not effect the net enthalpy.

Mackenzie Stockton 2H

Yes! I think that since the steam first comes into contact with the air, and the system involving the steam is much hotter than the surrounding, the system naturally loses heat to the surroundings before it hits your face. Also, I feel that this would have to do with diffusion of this extremely hot ...

Mackenzie Stockton 2H

For endothermic Rxn (delta H is greater than 0, the forward reaction requires energy): increase temperature--> increases K --> the forward reaction is favored (reaction shifts to the right) decrease temperature --> decrease K --> reverse reaction is favored For exothermic reaction (delta H is negati...

Mackenzie Stockton 2H

Yes, that is correct!

Now, you set the Kp expression you provided equal to the given K value. Also, set up an ice table with initial, change, and equilibrium concentrations to attain your quadratic, solve for x, and then you can find the equilibrium pressures for all species.

Mackenzie Stockton 2H

Q = [P] / [R], so if Q<K, there is no way that the reactant concentration could be greater than the products and Q be <K.

Mackenzie Stockton 2H

I= initial concentration C= change in concentration E= equilibrium concentration. For a balanced reaction, you have the initial concentrations of each species (given, or 0). Many times you have the equilibrium conc of one of the species, with which you can find the change in concentration for each s...

Mackenzie Stockton 2H

Yes, there are trends (like group 1 and 2 metal oxides/hydroxides are strong bases) and also specific strong acids and bases you should memorize, found in the textbook. When an acid protonates, it forms is conjugate base. When a base accepts the H+, it forms its conjugate acid. Heres an example: HCl...

Mackenzie Stockton 2H

Le Chatelier's principle holds that when a change is exerted on a system (like changing the concentration or pressure by changing the volume), the system will respond in a way that will minimize that change and return to "normal" Example: For the reaction A+ B --> C. Assume this reaction i...

Mackenzie Stockton 2H

We always use Kelvin for temperature in PV=nRT. This is simply because the units cancel out with the units of the other species in the equation.

Mackenzie Stockton 2H

I believe in lecture Dr. Lavelle said that an ideal gas is defined as a gas that does not undergo a phase change to a liquid when it is cooled. I believe that for this class, we assume all gases (assuming that they are a gas for a specific T and not a liquid that was cooled) are ideal and we can use...

Mackenzie Stockton 2H

One bar is about equal to one atm. There is a slight difference, but for the purpose of this class, you can use the two terms interchangeably.

Mackenzie Stockton 2H

I= initial concentration. This is the concentration of each reactant and product (mol/L) that you start off with C= change in concentration. The reactant usually will have a decrease in concentration that is proportional to the increase in concentration in the product. If there is one mol of a react...

Mackenzie Stockton 2H

Q can mean either Qp or Qc. Qp uses the partial pressures of each species (raised to a certain power if necessary), and is when all the elements in the equation are all gases, as solids and liquids can't exert partial pressure. Qc uses molar concentrations of each reactant and product (exclude solve...

Mackenzie Stockton 2H

T is constant because the temperature does not change when you are using PV=nRT. Although temperature in general can change, when we use PV=nRT we assume a certain set of conditions, in which Temperature is a set value.

Mackenzie Stockton 2H

Expanded octet just means that an atom utilizes its d block to hold more than 8 electrons in the valence, which is not possible with only s and p orbitals. The common expanded octets are P, S, Cl. Any atom in row 3 of the periodic table (in the p block) and below, can have an expanded octet because ...

Mackenzie Stockton 2H

The number in front is the energy level (n), or the principle quantum number. This specifies the different shells that the valence electrons are in.

Mackenzie Stockton 2H

See saw is AX4E , while trigonal pyramidal is AX3E

Mackenzie Stockton 2H

I think we just know that its square planar because Dr. Lavelle told us in class. Otherwise, theres no way to tell if somethings square planar vs tetrahedral if you cant see the Lone pairs. We know that only one O2 can bind to hemoglobin/the heme complex because the Fe is bonded to 4 N's and a hista...

Mackenzie Stockton 2H

I was also confused about this explanation the textbook gave. I do not think we have the memorize the pKA values or anything, I think that they were just provided in the textbook and we were supposed to reference them. Assuming we were not given the pKA values, I said that BrO- would be the stronger...

Mackenzie Stockton 2H

The quick answer is that whenever you see a compound with at least one polydenate ligand, that compound is a chelate. A chelate is a compound that is a ring-like structure, in which the polydenate ligand(s) form a ring which locks in the central TM atom. An example of a chelate is the heme complex. ...

Mackenzie Stockton 2H

Find the regions of electron density around that atom. Electron density refers to a Lone pair of electrons, or a bond (single, double, triple bonds all count as one region of electron density) If there is one region of e density - only uses s orbital two regions of e density- sp hybridization three ...

Mackenzie Stockton 2H

Water can act as an acid or base, it just depends. This makes sense if you think about Dr. Lavelle's discussion about how molecules do not just "choose" to be an acid or a base, and it depends on their chemical environment.

Mackenzie Stockton 2H

Polydenate means that the ligand binds with the TM more than once. So, polydendate ligands have at least 2 lone pairs, and they have to be long enough to stretch/bend in order to make 2/more coordinate covalent bonds with the TM. There needs to be single (Sigma) bonds that allow for this rotation. T...

Mackenzie Stockton 2H

For the chemical formula, the order does not really matter. Just make sure that you put the transition metal first, followed by all of the other ions and atoms.

Mackenzie Stockton 2H

Hybridization is a "mixing" of atomic orbitals in terms of energy. So, the hybridized orbital sp^3 is a mixing of one s and 3 p orbitals in terms of energy. Since this is true, the sp^3 hybrid orbital will have more energy than an unhybridized s orbital and less energy than a hybridized p ...

Mackenzie Stockton 2H

Yes, every bond is considered a region of electron density. Remember that a double bond and triple bond are bond considered one region of electron density, even though there is more than one bond.

Mackenzie Stockton 2H

it would be bent

there are 4 total electron density regions, with two being lone pair electrons and 2 being bonds

Mackenzie Stockton 2H

A molecule is polar if the dipoles on the diagram do not cancel out. So, the bonds themselves must be polar (there must be an electronegativity difference between the 2 atoms) and the bonds cannot cancel out, so there is a charge separation element too.

Mackenzie Stockton 2H

delocalized pi bonds occur when the molecule with the pi bond has resonance. Remember that resonance structures have atoms that all have the same bond lengths. For a resonance structure with double and single bonds, the actual bond length is in between double and single. Because all bond lengths hav...

Mackenzie Stockton 2H

Hybridization is a mathematical model that can be thought as a "mixing" of several orbitals in terms of energy. For ex, sp^2 hybridization creates a hybrid orbital that is a "mix" of one "s" and 2 "p" orbitals to create an sp^2 orbital that has an energy level...

Mackenzie Stockton 2H

Lewis bases- donate an electron pair in coordinate covalent bond. For atoms without a charge, look for lone pairs on the atoms which can be easily donated. Lewis acids- accept a lone pair of electrons in a coordinate covalent bond. For atoms without a charge, look for atoms like B that do not have a...

Mackenzie Stockton 2H

Electronegative, electron affinity, and ionization energy all have the same trends. They increase across a period, and decrease down a group. ionization energy has one exception- O has a lower ionization energy than N for electron-electron repulsion reasons (N has 3 unpaired e's in its p subshell wh...

Mackenzie Stockton 2H

Polarizability pertains to the anion. It is a measure of how easily their electrons can be distorted (and moved into the shared region, which is on the internuclear axis between two atoms in a bond). Larger anions have more electrons that are not as closely held to the nucleus, so they are more pola...

Mackenzie Stockton 2H

The best way to calculate formal charge is (number of valence electrons) - (dots) - (lines). Professor Lavelle covered another formula in class, but the formula I provided gives the same answer and is a lot faster.

Mackenzie Stockton 2H

We can predict the bond angles using VSPR, which is based on electron electron repulsion between lone pair electrons and bonding pair electrons. In terms of finding the exact value of the bond angles, this may not be always known, as many times the angles are described as being "less than"...

Mackenzie Stockton 2H

Look at the trends Bond length depends on the number of bonds (double, single, triple) and the size of the atoms You cant look at the periodic table for the number of bonds, but you can look for the size of the atoms atomic radius increases down a group (higher energy levels occupied with more elect...

Mackenzie Stockton 2H

Agreeing with what everyone has said, you look at the atomic radius (larger atomic radius means the electrons are less tightly held and more easily distorted). In terms of looking at this on the periodic table, Cl- is clearly the largest atom of all the ones on the list (because its on a lower perio...

Mackenzie Stockton 2H

Hi, I was also confused about this. But, since in lecture and all of the peer review sessions they have the arrow pointing to the more electronegative atom, I think that we should use this as the standard. It makes sense because the arrow represents the pulling of the electrons, and the more electro...

Mackenzie Stockton 2H

I dont think there is any set rule, but I like to draw the lewis structure with the lowest formal charge that I can think of and then quickly draw some other options just to make sure that it does in fact have the lowest possible formal charge. Helpful tips would be to make sure that the most electr...

Mackenzie Stockton 2H

The exceptions are: less than an octet: H, He- 2 electrons (usually) Li, Be - 4 electrons usually Al and Boron- won't always have less than an octet, but if they do they'll usually have 6 electrons in the valence radicals (7 valence e's) In terms of explaining this, it makes sense that H and He have...

Mackenzie Stockton 2H

Usually, we are looking to draw a lewis structure with a formal charge equal to zero, because this is the most stable form. Many times there are many different possible ways we can bond atoms in a molecule via a lewis structure, so considering formal charge is the way to figure out the "correct...

Mackenzie Stockton 2H

I don't think that you have to do that, at least for this class! However, I know that a double bond is stronger than a single bond, so that may be why you draw the double bonds as shorter in some cases.

Mackenzie Stockton 2H

It doesn't matter if its an electron, formal charge is the # of valence e's - (# dots) - (#lines) to put it simply. So if you get -1 when you do this, the Formal Charge would be -1.

Mackenzie Stockton 2H

Lower ionization energy (and thus lower electronegativity) has more space to accept bonds/electrons. So, it goes in the middle because this atom generally has the highest number of bonds in the atom

Mackenzie Stockton 2H

As you move right across a period, the number of protons increases (positive charge). This positive charge "pulls in" the negative electrons, so the electrons are closer to the nucleus (where the protons are). Because the electrons are more pulled closer to the nucleus as the number of pro...

Mackenzie Stockton 2H

For an electron to be excited, it has to absorb a photon of light with a frequency (v) that matches the specific energy difference between two energy levels/shells. After the electron is excited, it will eventually come back down to the lower energy state, emitting a photon with the same frequency/e...

Mackenzie Stockton 2H

The Hamiltonian of the wave function is equal to the energy of the wave function. Since the wave function is sin theta/cos theta, the Hamiltonian is taking the double derivative of the wave function (sin theta), which gives you back sin theta. because of this fact, you are given back the wave functi...

Mackenzie Stockton 2H

I believe that the measure of the atomic radius still exists, but at least for our purposes, we cannot calculate it from just a lone atom, only when it is interaction with another.

Mackenzie Stockton 2H

The position of a nodal plane also further differentiates an orbital from another (px, py, pz for example). The position of the nodal plane implies how the orbital is shaped and oriented.

Mackenzie Stockton 2H

I think the biggest reason for knowing the fourth quantum number is to understand that no 2 electrons can have the same 4 quantum numbers in an atom. The fourth quantum number provides the direction of spin.

Mackenzie Stockton 2H

The equations will give you the wavelength in meters (as long as all of the values you plug in are in SI units). However, you can give the answer in m or nm, but since our midterm is multiple choice, it should be clear which one they are asking for.

Mackenzie Stockton 2H

When it says delta x is equal to 10 m/s + or - 3, then the uncertainty in x would be 6

when it says delta x is 1% of the radius (or anything along these lines), take 1% of the specified value

When an electron or something is confined to the atom, the uncertainty is the diameter of the atom

Mackenzie Stockton 2H

Hi! Confirming what has already been said, light has momentum in the form of energy even though it does not have a mass. So, photons do have momentum but because they do not have mass, you cannot use the debroglie equation for a photon/EMR

Mackenzie Stockton 2H

I went to a UA session about this, and the statement technically depends on whether light is acting like a wave or a particle. If light is acting like a particle, increasing intensity increases the amplitude of the wave, so it would increase energy. If light is acting like a wave, increasing intensi...

Mackenzie Stockton 2H

For a particle-model, increasing intensity means increasing the amplitude, which increases the energy. This refers to increasing the intensity (brightness) of the light For a wave-like model, increasing intensity does not increase the energy because the EMR is acting like a particle and not a wave. ...

Mackenzie Stockton 2H

Both equations are valid for calculating the energy of the photon. You would use either equation depending on what variables you are given.

Mackenzie Stockton 2H

Here are the general rules: Light can have both wave and particle properties, both are valid, but we just refer to light as a wave or particle depending on the situation. When we say light is acting like a wave, increasing intensity means increasing the amplitude of the wave, which increases energy ...

Mackenzie Stockton 2H

This is correct. Every day objects do not demonstrate diffraction patterns because their masses are large, so the value of their wavelength from the equation wavelength=h/momentum yields an extremely small wavelength. Because their wavelengths are so extremely small, we cannot measure/notice wavelik...

Mackenzie Stockton 2H

An electron transition means that an electron is either absorbing a photon (absorption) and going to a higher energy level (a higher n). An electron transition to a lower energy level entails the electron emitting a photon of light. The energy required or released for an electron to make an energy t...

Mackenzie Stockton 2H

yes, the threshold energy is the same as the work function. remember that this is equal to the amount of energy that is required to remove from electron from a certain element/atom (ejecting it so that the electron is no longer associated with the atom).

Mackenzie Stockton 2H

I also had this question. Fundamentals D (Nomenclature), which is part of the optional reading, is all about naming compounds and all the rules. It was very helpful and I would recommend looking at sections 1-4 if you're having difficulty because it really cleared it up for me!

Mackenzie Stockton 2H

E.21 Calculate the amount (in moles) and the number of molecules and formula units (or atoms, if indicated) in (a) 10.0 g of alumina, Al 2 O 3 ; (b) 25.92 mg of hydrogen fluoride, HF HF; (c) 1.55 mg of hydrogen peroxide, H 2 O 2 ; (d) 1.25 kg of glucose, C 6 H 12 O 6 ; (e) 4.37 g of nitrogen as N N ...

Mackenzie Stockton 2H

Hi, like others have said, the solute is the substance that is dissolved in the solvent. Just a tip to remember when dealing with dilution problems- the moles/amount of solute stays the same before and after you dilute a solution, only the concentration of the solute changes. The solute concentratio...

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