CHEMISTRY COMMUNITY

Sean Reyes 1J

The main difference between an electrolytic cell and a Galvanic cell is the direction in which energy is converted. For example, the electrolytic cell converts electrical to chemical energy, whereas a Galvanic cell converts chemical to electrical energy

Sean Reyes 1J

Electrolysis occurs in an electrolytic cell. During this process, electrical energy is converted into chemical energy. This means that electricity would be supplied to facilitate a non-spontaneous reaction. Electrolysis is generally used to plate certain metals, which is where gold-plated jewelry co...

Sean Reyes 1J

An ion-selective electrodes a sensor that converts the activity of a specific ion dissolved in a solution into an electrical potential. The voltage is theoretically then dependent on the logarithm of the ionic activity, according to the Nernst equation, which is:
E(cell) = Eº(cell) - (RT/nF * ln(Q))

Sean Reyes 1J

A Galvanic cell and a voltaic cell are the same thing. There are other cells, though, such as an electrolytic cell. A Galvanic/voltaic cell converts chemical energy into electrical energy. An electrolytic cell uses electrical energy to drive a non-spontaneous reaction i.e. converts electrical energy...

Sean Reyes 1J

Usually, you can find the oxidation numbers of an element in a compound by using the oxidation numbers of the other elements present in that same compound. For example, in MnO4-, you know that the oxidation number of oxygen is -2. Using that information, you can find the oxidation state of the manga...

Sean Reyes 1J

Because k represents the rate constant, the value of k will never change for a unique reaction. That is to say, k itself will stay stagnant for that particular reaction. "Multiplying the table" by a factor of two would just change the concentration of the reactants, which would change the ...

Sean Reyes 1J

The overall reaction order would be 2, yes. But in terms of each reactant, the rate is first order. The rate law you wrote down is correct, but because the order of each reaction is 1, then the overall reaction order is 2.

Sean Reyes 1J

The unit of k basically just needs to lead to the unit of concentration/second
A zero-order reaction means that k has a unit of M/s
A first-order reaction has a k with unit 1/s
A second-order reaction has a k with unit 1/M*s

Sean Reyes 1J

A first-order reaction means that increasing the concentration of the reactant by a certain factor will increase the rate of the reaction by the same factor. A second-order reaction means that increasing the concentration of the reactant by a certain factor will increase the rate of the reaction by ...

Sean Reyes 1J

In kinetics, the value of n basically just gives the order in terms of that specific reactant. For example, an n value of 1 would essentially mean first-order reaction in terms of that reactant. Adding each order gives the overall reaction order. The order of each essentially tells you how fast the ...

Sean Reyes 1J

You would just use a standard delta G if the reaction is held under standard conditions (1 M or 1 atm ; 25ºC) or if the question specifically calls for a standard Gibbs free energy.

Sean Reyes 1J

You would use an inert electrode such as Pt(s) in the case that there are no solid species given by a half-reaction.

Sean Reyes 1J

In regards to the equation:
Delta G = -nFE ,
the amount of moles of electrons you need is found when balancing the half-reactions. The value of n will depend on the final result, meaning after you multiply to find the lowest stoichiometric coefficients needed to balance the entire reaction.

Sean Reyes 1J

The cathode is where the reduction half-reaction occurs, while the anode is where the oxidation half-reaction occurs.
In high school, we were taught "Red cat" and "An ox" as an easy way of remembering which reaction occurs in which electrode.
Hope this helps!

Sean Reyes 1J

You would need the largest positive voltage of as a result of both the half-reactions combined due to the fact that the potential difference comes from the maximum potential that can be produced. This maximum potential difference is represented by the E(cell). Additionally, the E(cell) must be posit...

Sean Reyes 1J

You can set P1V1 = P2V2 according to the Boyle’s Law, and then from there you can just divide out, which leads to:
P1/P2 = V2/V1

Sean Reyes 1J

A spontaneous reaction essentially means that the reaction will occur without the need of an energy input. That is to say, the reaction will proceed on its own, as someone else has already put it.

Sean Reyes 1J

When delta G is negative, this signifies that a reaction will proceed spontaneously. If delta G is postive, this means that the reverse reaction will be spontaneous and the forward reaction will be non spontaneous. Delta G is guaranteed to be negative when delta H is negative and delta S is positive...

Sean Reyes 1J

A bomb calorimeter take into account constant volume, whereas a normal calorimeter, such as a coffee-cup calorimeter, utilizes a constant pressure. When doing calculations involving a calorimeter, the value of the specific heat of the calorimeter using a constant pressure will be greater than the sp...

Sean Reyes 1J

I would take into account the context of the problem; if the problem uses kJ, then I would give an answer of heat with kJ as the unit. But if the problem used just J, then I would use J as the unit.
Hope this helps!

Sean Reyes 1J

Hi, I was just looking at my lecture notes and I didn't really understand why entropy is a maximum at equilibrium? Thanks!

Sean Reyes 1J

Because both heat and matter can not be transferred into or out of the system, there wouldn’t really be any changes in regards to heat. Because no change in heat is involved, I don’t think there would be any calculations to be done at least in regards to thermodynamics

Sean Reyes 1J

Delta U is basically the change of the internal energy of the system. Energy can be transferred into the system through the transfer of heat (which is represented through q) or with work being done onto the system (which is represented through w)
Hope this helps!!

Sean Reyes 1J

Work is the transfer of energy to a system through non-thermodynamic situations (basically just not through temperature differences). Work done on a system results in a positive value of w, while work done BY the system results in a negative value of w. Heat, in terms of thermodynamics, refers to th...

Sean Reyes 1J

If the problem didn’t give you K, then the value of Q wouldn’t make sense as you have nothing to compare it to.

Sean Reyes 1J

We can use the amount of moles on each side of the reaction to justify this. Because there is one mole of Cl2 on the reactants side and 2 moles of Cl in the products side, and increase in the pressure (through reduction of volume) would favor the reaction that produces less moles of gas, in this cas...

Sean Reyes 1J

Because in an endothermic reaction, heat is used to form the product, you can essentially treat heat as a reactant. Decreasing the amount of heat means you are decreasing the amount of reactants, and thus the equilibrium would favor the direction of the reverse reaction. Also, like already stated, t...

Sean Reyes 1J

I think it's because the addition of more reactants wouldn't result in a different equilibrium constant, it would just result in a new reaction quotient Q. Adding in more reactants would decrease the value of Q, which means that K>Q and that the reaction would favor the forward direction, not necess...

Sean Reyes 1J

If you were to write out the equilibrium constant for the concentrations of an acid, it would look like the following with the example using the acid ammonium: Ka = [H3O+][NH3] / [NH4+] Same goes for a base, using ammonia as the base: Kb = [OH-][NH4+] / [NH3] When multiplying these together, you wou...

Sean Reyes 1J

K is the equilibrium constant, meaning to calculate it, you must use equilibrium concentrations/partial pressures. Q is the reaction quotient and is calculated the same way as K, except using non-equilibrium concentrations/partial pressures. In comparing the two values (K and Q), you can find which ...

Sean Reyes 1J

Saying that the reverse reaction is spontaneous just means that the reverse reaction will occur and products will decompose to form reactants.
Hope this helps!

Sean Reyes 1J

Equilibrium constants help show whether or not there would be more reactants or products at equilibrium. For example, if K=100, that would mean that there are more products than reactants as this value is greater than 1. Also, the equilibrium constant can be compared to the reaction quotient to find...

Sean Reyes 1J

Because part A) is in terms of gases, you would use the partial pressures of the gases.

Sean Reyes 1J

Sodium bisoxalato(diaqua)ferrate(III) The answer is Na[Fe(OH2)2(C2O4)2] From this, you know that sodium will be acting as a cation and the coordination compound would have a negative charge (hence the suffix -ate). Ferrate is related to the element iron, which is why Fe is written. Iron also has a c...

Sean Reyes 1J

Thank you!

Sean Reyes 1J

I was just wondering whether or not we've covered bond order in lecture and what exactly is bond order?

Sean Reyes 1J

a) [Fe(CN)6]4- Okay so for this example, if you were to look up the oxidation number of CN, you'll see that it has a -1 charge. Because there are 6, that means the charge of the iron must be +2 as the overall charge must come out to be -4. I hope that made sense. Basically: (oxidation of Fe) + 6(-1)...

Sean Reyes 1J

When a strong acid dissociates, this yields a high concentration of H+ ions. Using the equation pH=-log[H+], you will find that the pH is very low which correlates to a strong acid.

Sean Reyes 1J

I realized I kind of didn't answer the question, my bad ahhhhh If the state of HCL is not mentioned, then depending on the context of the reaction you can see what state it is. For example, if it is reacting with water to form hydronium ions and chloride ions, then it is most likely acting as an aci...

Sean Reyes 1J

Most acids must be aqueous as this implies the idea that the acid can dissociate when in solution. This follows the Arrhenius definition of an acid, as this definition basically means that the acid will dissociate into its conjugate base along with an H+ ion.

Sean Reyes 1J

If you're basing this off a Lewis structure, then finding the amount of sigma and pi bonds is actually not too bad. Basically, every single bond is counted as a sigma bond, every double bond is counted as both a sigma AND a pi bond, and every triple bond is counted as a sigma bond and TWO pi bonds. ...

Sean Reyes 1J

Be is one of the exceptions to the octet rule along with hydrogen, helium, and lithium. Because beryllium does not have enough electrons at all to form an octet, it would only be able to from a single bond with each of the carbons. Additonally,if you used formal charge, the formula would be: 2 - ( 0...

Sean Reyes 1J

"A" is simply the notation for the central atom. "X" stands for the amount of bonded atoms (not bonds total, the amount of atoms attached) "E" is the number of lone pairs. For example, the VSEPR formula for CH4 would be AX4 since there are no lone pairs on the carbon an...

Sean Reyes 1J

Using the formal charge equation and with tine having two single bonds and one lone pair, tin would be:
FC = 4 - (2 + (4/2)) = 4 - (2 + 2) = 0.
This means that there is a formal charge of 0, which represents a pretty stable compound.

Sean Reyes 1J

Energy is required to form bonds. Because these are forming attractions with other molecules, this formation of bonds implies an exothermic reaction, which relates to a negative energy of the system

Sean Reyes 1J

Drawing the Lewis structure helps show the possible ways in which attraction can occur. For example, if you drew two water molecules side by side, you would notice the difference in electron density between the two molecules. This would lead you to draw the oxygen atom of one molecule being attracte...

Sean Reyes 1J

Hydrogen is an intermolecular force between the hydrogen in one molecule being attracted to a hydrogen/oxygen/nitrogen/fluorine in another molecule. For example, the hydrogen in one water molecule being attracted to the oxygen in another water molecule. This is also a type of dipole-dipole attractio...

Sean Reyes 1J

Atomic radius decreases across a period because of the pull that the protons have on the outermost shell. Across a period, the amount of core electrons doesn't increase, which means there is a higher effective nuclear force across a period. This results in a stronger pull on the electron cloud, effe...

Sean Reyes 1J

The exceptions that copper and chromium have in their d-orbitals are different than having an expanded octet (which exist when n>2). Because these elements exist in the transition metals, they have really weird rules as to how their valence electrons work. But yes, copper and chromium would have one...

Sean Reyes 1J

Polarizability tends to deal with the anion, while polarizing power deals with the cation.
The more polarizable an anion is, the more easily the electron cloud around it can be distorted.
The higher the polarizing power, the easier it is for the cation to distort an anion's electron cloud.

Sean Reyes 1J

You would be correct in saying that. Because there will always be a difference in electronegativity/electron affinity,the cation in the ionic bond will exert an electrostatic attraction on the electron surrounding the anion. This would distort the electron cloud, implying the concept of polarization...

Sean Reyes 1J

Degeneracy is basically having the same value of n. For example, if you were told to find the amount of degenerate orbitals in a 3p orbitals, there would be three different sets of quantum numbers you could use (because the spin of electrons doesn't matter in this situation): -(3,1,-1) -(3,1,0) -(3,...

Sean Reyes 1J

The loss of electrons means that the protons will have a stronger pull on the core electrons, as the charge is now positive. This means the electron cloud will decrease in size.

Sean Reyes 1J

We mainly need to know the relationship between n, l, and ml in that ml is dependent on l, which is also dependent on n.
So, for example, knowing that n =3 and l=2, that means that ml could take on the values: -2,-1,0,+1,+2.
Hope this helps!

Sean Reyes 1J

If n=2, that means that l could be equal to either 0 or 1.
In the case of l=0, that means that ml=0.
In the case of l=1, that means ml=-1,0,+1.
This gives a possibility of having 4 orbitals altogether.

Sean Reyes 1J

Delta v just implies the range of values that velocity could take on.
So if you are given +57/-4, then the values that velocity could take on ranges between those 61 values of velocity.

Sean Reyes 1J

When given l, the number of orbitals in a sub shell ranges from:
l,(l-1), ... , -l

Sean Reyes 1J

The quantum numbers, which you have labeled as (x,y,z), are actually numbers used to describe the specifics of an electron in an atom. (x,y,z) become (n,l,ml,ms) in the wave function. n is the principle quantum number and describes the shell. l describes the shape of the orbital. ml describes the su...

Sean Reyes 1J

Schrodinger's Wave Function gives a description of a specific electron for an atom, since no two electrons in the same atom have the same four quantum numbers. There aren't really any units to this, at least not any that have really been discussed in lecture as of yet. The four quantum numbers in ta...

Sean Reyes 1J

Also, depending on what the question calls for, use the corresponding units.
So if the question asks for an answer in Hertz, obviously just use Hertz. But for equations, they use s^-1, implying that s^-1 is usually meant more for calculations.

Sean Reyes 1J

Hertz (Hz) and s^-1 are the same thing.

1 Hz = 1 s^-1

Sean Reyes 1J

For the fourth row, you can use the equation of c=v * (wavelength) to find the value for frequency. Using that value of frequency, you can find the energy of the photon using E=hv. Depending on the value of the wavelength, you can then determine which type of electromagnetic radiation it is.

Sean Reyes 1J

When an electron moves from a higher energy level to a lower energy level, the change in energy is negative, which you understood. The reason we used a positive value when using the equation, E=hv, is because we were using the energy of the photon emitted. When a photon is released, the photon will ...

Sean Reyes 1J

The metal hydroxide, shown as M(OH)2, has a molar mass of 74.10 g/mol. Hydroxide alone has a charge of -1, which would imply that the metal has a charge of +2 since there are 2 hydroxides per metal. Sulfur when ionized has a charge of +2, which would mean that the salt would look like: MS. Using the...

Sean Reyes 1J

I just realized I didn't even answer the question my bad hhhhhh. But using the moles found from part a of O2 and of P4O6, you would convert both to moles of P4O10 using stoichiometry. The lower amount is the maximum amount that you would theoretically be able to create in a lab experiment. Then, usi...

Sean Reyes 1J

The limiting reactant overall for BOTH reactions together is O2. Using only the first chemical reaction may make it seem as though the P4 is the limiting reactant, but when looking at both reactions in the formation of P4O10, O2 is found to be the limiting reactant. Given that both white phosphorus ...

Sean Reyes 1J

The prefix "hepta-" implies that there are 7 water molecules.
This would mean that the compound would be written, in its entirety, as:
MgSO4 ・ 7H20

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