CHEMISTRY COMMUNITY

Charysa Santos 4G

The more positive/less negative Ecell value is typically correlated to the cathode (reduced), and the more negative Ecell value is correlated to the anode (oxidized).

Charysa Santos 4G

Platinum (solid) is needed when there is no electrode for a given anode/cathode.

Charysa Santos 4G

If bonds are being broken, then that is endothermic (requires energy), but if bonds are being made then that is generally exothermic (releases energy).

Charysa Santos 4G

My TA said that she still has to input all of our homework grades, but I'm sure they should be out by around next weekend, like last time. However, due to the circumstances, I'm not sure when exactly they will be posted.

Charysa Santos 4G

ayushibanerjee06 wrote:it said that all inorganic phosphate came from ADP so you can use the stoichiometry to find how much Pi you have. you can calculate Q from there

I believe that the question stated that the phosphate actually came from ATP, not ADP

Charysa Santos 4G

Hi, can someone walk me through the steps of how to solve for the rate constant? In particular, I don't understand where the 0.59 value comes from (as per the solutions manual).

Charysa Santos 4G

Changing the mass of the electrodes will not affect cell potential, only the time of the reaction.

Charysa Santos 4G

You must find n by balancing the half reactions and seeing how many electrons are transferred (which is your n value)

Charysa Santos 4G

Because solids and liquids do not have a concentration, they are not included in the rate law.

Charysa Santos 4G

It is pretty much the same as balancing a reaction in an acidic solution, but you must balance the Hydrogens with OH- instead of H+

Charysa Santos 4G

We use an inert solid when there is none present in the anode, cathode, or both. It varies from case to case, so it isn't always at one end or the other, or even both.

Charysa Santos 4G

You would simply use a Platinum electrode where there isn't a solid metal electrode present for a certain cell.

Charysa Santos 4G

OH- and H+ can be both reactants and products in your redox reaction. This varies case to case, so you would have to balance each of your half reactions and see what needs to be balanced in order to determine where the OH- or H+ is needed.

Charysa Santos 4G

An oxidizing agent refers to the item being reduced, which allows for the other species to be oxidized. A reducing agent is exactly the opposite: it is being oxidized in order for another species to be reduced.

Charysa Santos 4G

When the solution is acidic, H2O is added in order to balance the oxygen, and H+ is used when balancing the hydrogens. However, It is usually safest to balance the oxygen before balancing the hydrogens.

Charysa Santos 4G

Yes, I believe they only taught us one way to write a cell diagram, so we can use it for both.

Charysa Santos 4G

A half reaction is either the reduction reaction (gaining electrons) or oxidation reaction (losing electrons) that make up your redox reaction.

Charysa Santos 4G

I found that this Khan Academy video may be helpful/relevant in answering your question: https://www.khanacademy.org/science/che ... ree-energy

Charysa Santos 4G

https://www.youtube.com/watch?v=B_em0quwuSw --> I found this video to be helpful in explaining the rusting process and how it relates to redox reactions

Charysa Santos 4G

Le Chatelier's Principle just refers to how adding more of a substance in either cell can cause movement of cell potential either up or down depending on what you are adding and to which side of the reaction it belongs to (reduction or oxidation).

Charysa Santos 4G

A half reaction is either the reduction reaction or oxidation reaction that comprise the redox reaction

Charysa Santos 4G

Delta S of the system is the entropy of the system, Delta S of the surroundings is the entropy of the surroundings (usually just the opposite/negative of Delta S), and the Delta S (total) is 0 for isothermal reversible reactions and is usually equal to Delta S (sys) for irreversible reactions.

Charysa Santos 4G

Phase changes correlate to the plateau of a heating curve, and there, you can use q = mΔh if you are given mass or q = nΔh if you are given moles. If you are calculating the diagonal/rise in temperature, you will use q = mCΔT or q = nCΔT.

Charysa Santos 4G

PV = nRT can be used at STP if you plug in 273.15 Kelvin for the temperature (T) and 1 atm for pressure (P)

Charysa Santos 4G

Exothermic reactions are generally spontaneous, because unlike endothermic reactions, they do not require heat input

Charysa Santos 4G

Think of energy/heat being a reactant in endothermic reactions (heat must be supplied), and as a product in exothermic reactions (heat is being released). So when you increase temperature in an endothermic reaction, you are increasing the amount of reactants so the reaction will favor the products, ...

Charysa Santos 4G

The K of a reverse reaction is just the inverse of K (or 1/K)

Charysa Santos 4G

You can tell that a reaction is spontaneous when Gibbs free energy (delta G) is negative, which means that it is releasing free energy.

Charysa Santos 4G

Delta H is equal to q + w, so when there is no work being done on or by the system (or when w = 0), then delta H = q

Charysa Santos 4G

For each mole of lead, there are more protons, electrons, and neutrons than in carbon, so on a sub-atomic level, there is more entropy because these particles' movements contribute to the atom's overall entropy.

Charysa Santos 4G

Bond enthalpy questions usually give you the reaction (A + B --> C) and then you just look at each molecule that is in the reaction and look up their bond enthalpy values. Bonds broken are usually correlated to those of the reactants and bonds formed correlate to those of the products.

Charysa Santos 4G

Positive work = the surroundings are doing work on the system (i.e. positive delta H when heat (energy) is being added to a system)
Negative work = the system is doing work to its surroundings (i.e. negative delta H when heat (energy) is leaving a system)

Charysa Santos 4G

HF is not a strong acid, therefore it does not completely ionize (100%)

Charysa Santos 4G

P = Pressure, V = Volume, n = number of moles, R = gas constant, and T = Temperature

Charysa Santos 4G

A negative delta H is exothermic because that means that energy is leaving (-) the system.

Charysa Santos 4G

If Q is less than K, that means that the ratio of products to reactants is lower than at equilibrium, so the reaction will favor the products. If the Q is greater than K, then the ratio of products to reactants is higher than at equilibrium, so the reaction will favor the reactants.

Charysa Santos 4G

The gas constant (R) depends on what other units are given to you when calculating PV = nRT. The units are included on the formula/equation sheet.

Charysa Santos 4G

PV = nRT is the Ideal Gas Constant, so it applies to gases, not aqueous solutions.

Charysa Santos 4G

The R depends on what other units you are working with in your PV = nRT calculation.

Charysa Santos 4G

If your K is less than 10^-3, you can approximate the denominator.

Charysa Santos 4G

If they give you the pKa, they would likely also have given the concentration of either [OH-] or [H3O+] or you would have to solve for them, and then you could use that value to do -log([H3O+]/[OH-]) and find the pH/pOH.

Charysa Santos 4G

If the given K is less than 10^-3, then you can use approximation, meaning that you can disregard the X because it is small enough that it would not profoundly impact your equilibrium expression.

Charysa Santos 4G

If you know the pH, for example pH = 6, then according to the equation pH + pOH = 14 (derived from pKw = pH + pOH) then you would just set pOH = 14 - pH (6) so your pOH would equal 8.

Charysa Santos 4G

It's just a general rule to check whether or not your approximation is valid because the amount (X) should be small enough that it wouldn't profoundly impact your equilibrium expression.

Charysa Santos 4G

The 5% rule is for checking whether or not your approximation is valid. This is usually if the K is less than 10^-3 and you take out the X from the denominator of your equilibrium expression.

Charysa Santos 4G

You can only take out the X in the denominator if the K is less than 10^-3. The ice box helps to visualize and take inventory of what you start with and what is changing at the equilibrium.

Charysa Santos 4G

Kp is more particular to gases, and Kc applies to when concentrations are being used, so it would probably be safer to use Kc or just to leave K as is. I’m not completely sure, though...

Charysa Santos 4G

*Kc can be used for when concentrations are being used, while Kp is more particular to partial pressures and is more specific to gases.

Charysa Santos 4G

If all of the reactants and products are in the gas phase, then you must use Kp if only the partial pressures are given. Kc* is used for concentrations, and is thus used when the reactants and products are in the aqueous phase. I think it depends on what you are given.

Charysa Santos 4G

The coefficients are attached to the particular reactant/product as you balance the equation. This coefficient becomes the exponent to the same reactant/product when calculating Q or K.

Charysa Santos 4G

As the others have said, because Q is calculated in the same manner as K, solids and pure liquids are not included in the expression.

Charysa Santos 4G

Some solutions to reducing the acidity of the rain could include producing less excess carbon dioxide or sulfur dioxide in the atmosphere so that these gases do not react with the H2O to form acids. I'm not sure if that answers your question about "lessening the acidity," though.

Charysa Santos 4G

Yes, hydrogen bonding would result in a higher boiling point because compared to the PH3, Nitrogen has far greater electronegativity, which means that it is able to form much stronger (hydrogen) bonds which require more energy to break (as in boiling).

Charysa Santos 4G

Yes, because the polydentates have multiple binding sites, they are able to form a "claw" or loop around the metal cation.

Charysa Santos 4G

Also, as a follow-up, how can we tell whether the metal -- in conjunction with the fact that it is attached to a conjugate base from a strong acid -- will produce either a basic or acidic pH in solution?

Charysa Santos 4G

For parts (e) and (f), I get that they're acidic because the conjugate bases come from strong acids (HCl and HNO3, respectively), but how would you be able to tell that the cation would have to be analyzed rather than the anion?

Charysa Santos 4G

How do we find out which base is stronger -- either BrO- or C17H19O3N -- without knowing the pKb value?

Charysa Santos 4G

Lewis bases usually have a lone pair so that it has electrons to donate while Lewis acids usually have a positive charge attached to them, meaning that they will likely accept an electron pair.

Charysa Santos 4G

My test 2 grade is also a 0/50, as well... I believe that the TA's should input these at a later time, though. I'm not sure why, but my homework category is also a 0/50 even though my TA hasn't technically collected all of our homework yet.

Charysa Santos 4G

If you want to calculate the charges using your knowledge of the periodic table and elemental charges that occur from it, you could do that, but it is time consuming and tedious. Like the person above mentioned, it would be in your best interest to just memorize these charges in order to conserve ti...

Charysa Santos 4G

Due to a water molecule's orbital geometry, only one of its lone pairs can be correctly oriented to 'bond' while the other lone pair will point away from the central atom.

Charysa Santos 4G

The difference is that Bronsted acids and bases focus on the exchange of H+ ions (protons) while Lewis acids and bases deal with the exchange of electrons.

Charysa Santos 4G

Which is stronger: a sigma or a pi bond, and why?

Charysa Santos 4G

Using the VSEPR formula, AX4 is tetrahedral because it has no lone pairs (E). However, if it is AX4E2, the shape is square planar because the two lone pairs of electrons cause the bonded electrons to be arranged in a square shape, which allows them to be farthest from one another.

Charysa Santos 4G

You must also indicate that there is a sigma bond present, in addition to the pi bond.

Charysa Santos 4G

If the molecule has 3 regions of electron density, but one is a lone pair, then it can be bent (< 120 degrees). However, if the molecule has 4 regions of electron density, and two of them are lone pairs, then it can also be bent (< 109.5 degrees).

Charysa Santos 4G

Sigma bonds overlap end to end while pi bonds overlap side by side, with one nodal plane containing the internuclear axis.

Charysa Santos 4G

Bent and angular refer to the same type of shape. Either works when naming AX2E and AX2E2 molecules.

Charysa Santos 4G

Because smaller, highly charged cations (which, due to their lower electronegativity, have lose electrons) have smaller radii, the force of their positively-charged nucleus can better attract electrons, causing their polarizing power to be larger.

Charysa Santos 4G

Essentially, if we go by periodic trends, Ba has the biggest electronegativity difference with Br compared to B and Be, making it the most ionic bond (ionic bond strength increases as the electronegativity difference increases between to atoms).

Charysa Santos 4G

Because there is an uneven charge distribution (of electrons) between S and O (oxygen is more electronegative), there are dipole moments that form between them, creating dipole interactions.

Charysa Santos 4G

No, only hydrogen atoms that are bonded to nitrogen, oxygen, and fluorine are able to form hydrogen bonds.

Charysa Santos 4G

A lone electron pair will repel its surroundings more than a bonded electron would because its negative charge isn't being distributed/shared unlike the bonded pair, thus its negative charge and repulsion is more concentrated/stronger.

Charysa Santos 4G

Ionic bonds are the strongest because the electrons are actually being donated to the more electronegative atom, and thus it would be hardest to pull these apart because it would take a relatively large amount of energy to remove electron(s) from such pairings

Charysa Santos 4G

In order for a molecule to form hydrogen bonds, at least one hydrogen atom in the molecule must be bonded to either a oxygen, nitrogen, or fluorine atom.

Charysa Santos 4G

I think that the bond lengths are more of an arbitrary approximation to gauge which atoms share how many electrons between their electron clouds. The more electrons that they share in close proximity (i.e. how many bonds they have between each other), the closer the electrons will be between those a...

Charysa Santos 4G

The angular momentum quantum number for the d subshell is l=2, and its corresponding magnetic quantum numbers can have the values -2, -1, 0, 1,& 2 (5 in total). In each of these, there can be 2 electrons, which means that there are a total of 10 electrons that can be placed in the d subshell.

Charysa Santos 4G

An anion has a larger radius than its neutral atom because when you add an electron, the repulsive forces between the electrons is relatively greater than the pull of the positively-charged nucleus, thus causing the electrons to further apart, making the anion's radius larger.

Charysa Santos 4G

When energy is absorbed by an atom, it is receiving energy, so the change in energy is positive, causing an electron to become excited and move from a lower energy level (let's say, n=1) to a higher energy level (i.e. n=2).

Charysa Santos 4G

Ah, so because it's asking for a +2 metal, the ion's electron configuration for the d orbital is still the same as the neutral atom's because you're taking the 2 electrons from the s orbital... Understood!

Charysa Santos 4G

And also, can someone explain why this also applies to part (b), and why it is Fe^2+?

Charysa Santos 4G

Why would the M^2+ metal for [Ar]3d^7 be Co^2+? Shouldn't it be Cu^2+ since the metal in question supposedly lost 2 electrons and now has the electron configuration [Ar]3d^7?

Charysa Santos 4G

No, the noble gases do not follow the periodic trends (i.e. electronegativity, electron affinity, etc.) the way that the Group 1, 2, and so on elements do. They each have a complete valence shell, so they do not usually attract electrons.

Charysa Santos 4G

The bond length is determined by how many bonded electrons there are. The more electrons are bonded (i.e. a triple bond in which 6 electrons are bonded), the shorter the bond length. That means that a triple bond has the shortest length (and has the most attraction/energy bringing the two atoms toge...

Charysa Santos 4G

The lone pairs of the electrons found on neighboring atoms weaken these bonds due to electron repulsion. The neighboring atoms in a molecule that have lone pair electrons are not bonded as tightly because the lone pair electrons of both atoms repel one another.

Charysa Santos 4G

Electron affinity increases rightwards across a row, and then decreases downward, down a group/column.

Charysa Santos 4G

Anions are generally larger than its corresponding neutral atom because adding electrons increases the number of electron-electron repulsion interactions that take place. Cations are smaller than the corresponding neutral atoms, since the valence electrons, which are furthest away from the nucleus, ...

Charysa Santos 4G

Just think of it as having to insert energy (+) in order to take out the electron because the electron is being held to the atom by the positive charge of the nucleus.

Charysa Santos 4G

If there are multiple places where the center atom can bond with the outer atoms and these bonds are interchangeable, I believe that you just have to count/take account of all of these different forms to get the number of resonance structures.

Charysa Santos 4G

Electron affinity is simply the potential of an atom to accept an electron (or more than one) based on its size (how many shells does it have/how far is its valence shell from its nucleus) and whether or not it almost has a full valence shell (lefthand side of the periodic table of elements tend to ...

Charysa Santos 4G

Fluorine is the most electronegative element because it almost has a full valence shell, and since its atomic radius is relatively smaller than the other elements in its column/group, the positively-charged nucleus has a higher chance of attracting the last negatively charged electron to fill this s...

Charysa Santos 4G

An ionic bond is usually between a cation and an anion, and there is a transfer of electrons between the two. However, with covalent bonds, the electrons are merely shared between the two atoms.

Charysa Santos 4G

I believe that it is only momentarily "removed" from the metal, but the only possible way for it to "leave" the metal is if there is excess energy (if the photon's energy is greater than the energy to remove the electron) and in that situation, the electron is ejected from the me...

Charysa Santos 4G

I forgot to add that you can also use De Broglie's if you are given the wavelength and you need to find either mass or velocity (λ = h/mv).

Charysa Santos 4G

If you're dealing with quantum numbers and atomic orbitals in a question, you will most likely use Schrodinger's wave function equation. De Broglie's would be to find the wavelength (for instance, if you are given the mass and/or velocity of an object, then you would use De Broglie's equation).

Charysa Santos 4G

Oh, I see, I didn't realize at first that it was a constant. Thank you!

Charysa Santos 4G

In the solutions manual, can someone explain where the 1.6022x10^-19 J*Ev^-1 comes from when converting the given value in the problem to Joules?

Charysa Santos 4G

It depends on what you are given. They will usually ask for it, or if they give you the experimental data for something like a problem where you have to find the empirical formula, then you should calculate it to help you with the final answer.

Charysa Santos 4G

I remember Prof. Lavelle suggesting that we should convert the fractional stoichiometric coefficients into whole integers.

Charysa Santos 4G

My TA said that to be safe and secure partial credit in the case that your final answer is somehow incorrect, you should show as many steps as possible/necessary to indicate each step of a problem. It is totally up to you, though.

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