CHEMISTRY COMMUNITY

Andrew Yoon 3L

What would the standard conditions be? Would it just be 1 mol at 298 K?

Andrew Yoon 3L

N represents the number of moles of electrons that are being transferred in the reaction. You can only find N once you have balanced out the equation.

Andrew Yoon 3L

To find the activation energy of the reverse reaction, you add the activation energy and the positive delta H (this is when the bonds are being broken down).

Andrew Yoon 3L

Is the rate always going to depend on the reactant with smallest concentration? A pseudo rate is considered when there are too many changing concentrations. For instance, it is difficult to calculate the rate when you have k[A][B], and both A and B are changing. As such, you make one significantly ...

Andrew Yoon 3L

I think the dt at the end of the equation is used for derivatives/calculus. I don't think it'll come up on the final.

Andrew Yoon 3L

I first thought of the plugging in 1 to both [A] and [B]. Once plugging 1 in and solving for the rate, it would come out as just 1. Then, I plugged in the new numbers: 1/2 to [A] and 3 to [B]. The rate comes out as 9/2. 9/2 is the factor of which the rate would change when the [A] was halved and [B]...

Andrew Yoon 3L

When you solve for the average rate, the answer may appear as a negative number. However, it should always be positive we are looking at the forward reaction. Dr. Lavelle mentioned it lecture about it.

Andrew Yoon 3L

How do we know that an element/compound is created/made? I know that catalysts aren't formed or used up but appear on both sides of a process of reactions. Also, if they appear on both sides, would they appear on the final rate law?

Andrew Yoon 3L

The second order reaction is derived from the second order integrated rate law, which is 1/[A]=kt+1/[A]0. This equation involves the concentrations as well as the rate constant of the second-order reaction.

Andrew Yoon 3L

I was wondering how you would find the substitute of [HClO]? Like how would you know what to put on the reactants and the products side?

Andrew Yoon 3L

To find whether the reaction is spontaneous or not, you use the equation ∆G˚=-nFE˚. If E˚> 0, then ∆G˚ would be negative, making the reaction spontaneous. If Eº < 0, then ∆G˚ would be positive, making the reaction not spontaneous.

Andrew Yoon 3L

Standard Gibbs free energy is a fixed value for a reaction under standard conditions. Gibbs free energy is the energy that is available to do work and transfer in and out of the system.

Andrew Yoon 3L

I think your E˚cell value is might be wrong. I got E˚cell = 1.758V, but everything else looks correct! So it shoud be, G˚ = -(6 mol)(F Cmol-1)(1.758 V) / 1000 J.

Andrew Yoon 3L

To find the cell potential, you need to use the Nernst equation. Eo − [(RT)/(nF)]ln(Q). You find Eo by subtracting the standard cell potential of the cathode by that of the anode. The n is the number of electrons transferred, and F is Faraday's constant. Q can be found by using the given concentrati...

Andrew Yoon 3L

For this problem, you use the Nernst Equation. However, instead of lnQ, you use logQ. Eo would be 0V because we are under S.H.E. Q in this question would equal PH2/[H+]^2.

Andrew Yoon 3L

Oxygen will have an oxidation number of 0 when it is in its natural state (so when it's O2 or O3) When oxygen is in a compound, (i.e. KClO2) it will have an oxidation number of -2.

Andrew Yoon 3L

To draw/write out a salt diagram, I think it's best to place the anode on the left and the cathode on the right. However, it kinda depends on on the diagram and equation. The electron flow goes from the anode to the cathode.

Andrew Yoon 3L

Oxidizing is when a substance is losing electrons. Reducing is when a substance is gaining an electron.

Andrew Yoon 3L

KClO2⟶KCl+O2 As an uncombined element, O2 has a oxidation number of 0. KClO2 and KCl are both ionic compounds. K in both compounds will have a charge of +1. That means Cl will be -1 in the KCl compound. However, this is not the case for KClO2. Since oxygen will have a charge of -2 when it is in a co...

Andrew Yoon 3L

For this problem, you first want to look at the charge of the element on both sides of the equation. The charges on both sides should be equal. So in the In⟶In3+ equation, there are 3 more electrons on the left side than the right. So, to balance it, we add 3 electrons on the right: ln⟶ ln3+ + 3e-. ...

Andrew Yoon 3L

A fuel cell is thermodynamically feasible when ΔG is negative, which would mean it would be spontaneous.

Andrew Yoon 3L

The entropy is higher when the atm is lower because at lower pressures, the volume is greater (volume and pressure are inversely proportional). With a greater volume, there is more states the particles can achieve. Therefore, there is a greater entropy (S). If the atm was higher, then the entropy wo...

Andrew Yoon 3L

∆U = 0 for an isothermal expansion of an ideal gas because the work that is done within the system is replaced by energy in the form of heat. This means that Q = -W, which also can be written as ∆U = Q + W, which also equals 0.

Andrew Yoon 3L

In lecture #14, Lavelle went over the relationship between ΔS with T(temp). What did he mean when he said that "the ΔH(rxn) plays an important role at low temperatures"? Can someone clarify how it relates back to the relationship between ΔS and T?

Andrew Yoon 3L

Delta G represents the change in free energy of the reaction. Delta G Knot represents the change in free energy of the reaction when it is under standard conditions.

Andrew Yoon 3L

Elements that are in its pure form are the most stable. So diatomic elements and other specific compounds (like graphite) are pure.

Andrew Yoon 3L

The pressure in an open system is going to be constant because it has little to no effect on the external pressure, which is the pressure of the atmosphere.

Andrew Yoon 3L

I think that those constants are used for ideal gases.

Andrew Yoon 3L

Work is represented by "w". "W" represents degeneracy.

Andrew Yoon 3L

Yes, I believe that delta U can equal 0. Delta U is zero when there is no change in internal energy, which would occur when the system is isolated.

Andrew Yoon 3L

Question 10 of the sapling deals with delta H of fusion, which deals with moles.

Andrew Yoon 3L

Enthalpy is the heat energy required to form and break bonds in a chemical reaction. It is represented as H. Entropy is the amount of disorder in a system. It is represented as S.

Andrew Yoon 3L

Enthalpy energy is the heat energy that is related to the forming and breaking of bonds in a chemical reaction. Internal energy is the total energy (kinetic and potential energy) in the system.

Andrew Yoon 3L

The standard enthalpy of formation be 0 only when the compound is in its most stable state. The diatomic molecules that are in the standard state are H2, N2, F2, O2, I2, Cl2, Br2. I believe it also depends on the phase they are in.

Andrew Yoon 3L

Thank you everyone for responding! I understand it now! :)

Andrew Yoon 3L

The ones I can remember he saying in class were graphite, O2, and H2. Were there any others he explicitly mention?

Andrew Yoon 3L

I believe he said that method 3 was the "best", but method 1 was also an accurate way to calculate enthalpy change. It really depends on what you're given in a problem.

Andrew Yoon 3L

When bonds are broken, energy is gained. This is related to the boiling/melting point of a compound. When bonds are formed, energy is released. This is related to freezing/condensing.

Andrew Yoon 3L

I'm still a bit confused on why steam causes more severe burns compared to water at 100°C. Is it because the energy that released when it touches someone's hand is still going to be the same temperature when it is a gas, compared to when it is a water, which would temperature would decrease as more ...

Andrew Yoon 3L

Phase change is when a phase (solid, gas, and liquid) either melting, boiling, or freezing. The process of a phase changing to another phase is a phase change. For example, ice that melts to water is a phase change: it is melting.

Andrew Yoon 3L

I'm not entirely sure if there is a high pressure that there will be an higher equilibrium constant. All that is important is that the equilibrium constant stays the same if we change the pressure or the volume. Only a change in temperature will change the k value.

Andrew Yoon 3L

Since the problem gives the moles of NH3 in the beginning of the reaction, you would write 0.2 mol/L for the initial concentration for NH3. Then, you would solve for x just how you would for any other ICE box.

Andrew Yoon 3L

When your squaring your products, make sure you are squaring both the variable and the coefficient. (2x)^2 should equal 4x^2. Next, you should multiply out the denominator. Then, you should solve for x using the quadratic formula.

Andrew Yoon 3L

H+ or OH- would have molar concentrations because when strong acids/bases react with water, they completely dissociate. H+ can also be written as H3O+. Since H+ and OH- are products in the reaction, they must have a concentration. Dissociation does not mean they disappear.

Andrew Yoon 3L

When decreasing the temp, the k value will increase. This is an exothermic reaction. You can also see if the reaction is exothermic if delta H is negative.

Andrew Yoon 3L

Just to ask, if we are given a value for the products in the question as well has initial values for the reactants, would we include them in the I part of the ICE table?

Andrew Yoon 3L

You have to change mmol to mol/L. First change to mmol to mol and then divide by volume (L) to get the molarity.

Andrew Yoon 3L

For this question, you would need to add two or more equations together. Adding equations together is the same as adding numbers except the substances on their sides, stay on their respective sides (so like on the left or on the right). Next, in order to get the equation to exactly match with all th...

Andrew Yoon 3L

"<<" refers to how much smaller (or larger depending on what you're looking at) the number/variable is compared to the other number/variable.

Andrew Yoon 3L

For Kc, you would use the molar concentration of the substances in the system. If the question asked you to find the Kp, you would use partial pressures of the substances in the system.

Andrew Yoon 3L

For acid rain, you should know that it is formed in the atmosphere when carbon dioxide reacts with water, which produces carbonic acid and becomes acid rain.

H2O + CO2 --> H2CO3

Andrew Yoon 3L

For bronsted acid and bases and lewis acids and bases, it's pretty clear on what is a conjugate acid/base. However, I'm not entirely sure if neutralized reactions have a conjugate acid and base. I don't think they do because the products are water and a salt.

Andrew Yoon 3L

^^ yeah an amphoteric compound is a compound that can be an acid or base in a reaction. The most basic example is water, H2O. Since it can both accept or donate an H+, it can be bronsted acid or base.

Andrew Yoon 3L

Yeah so polyprotic acid and bases accept/donate more than 1 proton, in other words H+.

Andrew Yoon 3L

Yeah just know the relationship between pH, pOH, [H+], [OH-]. If you know the relationships among them well, you should be good!

Andrew Yoon 3L

There are no such things as a strong or weak salt because salts do not affect the pH.

Andrew Yoon 3L

When NH3 interacts with H2O, it doesn't give up an H to H2O because H3O is very unstable. So rather, it will accept an H from H2O. The products would be NH4+ and OH-. Since it is accepting an H, which can be thought of as a proton, NH3 is an base and H2O is an acid.

Andrew Yoon 3L

Lewis acids and bases focus on the transfer of lone pairs of electrons. Bronstead acids and bases focus on the transfer protons.

Andrew Yoon 3L

(en) refers to ethylenediamine ligand, or NH2CH2CH2NH2. Ethylenediamine ligand is a bidentate ligand which has a coordination number of 2, and since there are 2 of en, the coordination number would 4. For CO, since there are 2 of it, it will form one ligand each as a monodentate, which will have a c...

Andrew Yoon 3L

The transition metals are elements in the d-block, which are groups 3-12. They also have valence electrons in at least two shells.

Andrew Yoon 3L

You have most of the name correct. The only parts you have wrong in the name is the chlorine and the cobalt. Since there are 2 Cl anions in the backets, it would be dichloro instead of chloro. For the cobalt, it would be cobalt (III) because of the assigned charge. Since, we don't know the oxidation...

Andrew Yoon 3L

An ionic liquid is a salt in a liquid state. It has a low melting point

Andrew Yoon 3L

Dipole-dipole interactions occur when both molecules that are interacting with one another are polar all the time. Dipole-induced-dipole interactions occur when there is a polar molecule interacting with a nonpolar molecule.

Andrew Yoon 3L

Both hemoglobins and myoglobins are hemeproteins. However, hemoglobins are found in red blood cells and diffuses oxygen throughout the body. This oxygen goes through the blood and tissues of the body. Myoglobins are found in muscle cells, and they store oxygen in the muscle cells.

Andrew Yoon 3L

Lewis acid is when accept electrons, while lewis bases donate electrons. Bronsted acids accept hydrogen protons, while Bronsted bases donate hydrogen protons

Andrew Yoon 3L

SO2, is a nonmetal oxide, which makes it a lewis acid. In addition, the shape of the SO2 is bent and it is polar. This causes the oxygen to attract more electrons, making it a lewis acid.

Andrew Yoon 3L

Although bond length definitely affects the strength of the bond, we also have to consider the intermolecular forces. Although both compounds only have LDF's. CCl4 has a higher boiling point than CH4 because it has stronger LDF interacting. This is due to it having more electron shells, which increa...

Andrew Yoon 3L

First, I would draw out the lewis structures for all of the compounds. You know all of them have LDP. Next, I would check for hydrogen bonding. That only happens between H and O, N, or F. Dipole-dipole interactions occur when a partially negative part apolar molecule is attracted to a partially posi...

Andrew Yoon 3L

Electron repulsion occurs when two of the same sign (negative and negative) come close to each other. They will repulse each other. Yes, electron repulsion does play a part in forming the shape of an atom.

Andrew Yoon 3L

Dispersion forces are forces between molecules; they hold the two molecules together. They are classified as intermolecular forces. Electronegativity is how often an atom attracts a shared pair of electrons, which connects two atoms together. Electronegativity determines intramolecular forces. Inter...

Andrew Yoon 3L

Cl has 17 electrons. It has 2 electrons in the first shell, 8 in the second shell, and 7 in the valence shell. The octet rule states that atoms will have 8 electrons in its valence electron. Cl will need one more electron to fill the valence shell and complete the octet rule. So 17 + 1 = 18 electrons.

Andrew Yoon 3L

@Maddie Turk

Yes, as the atomic radius increases, the electronegativity decreases. Because the electrons are further and further away from the nucleus of the element, the element becomes less active to attract electrons.

Andrew Yoon 3L

Yes the more stable molecule/better lewis structure would be when the central atom has a formal charge that is or very close to zero.

Andrew Yoon 3L

Yes the more stable molecule/better lewis structure would be when the central atom has a formal charge that is or very close to zero.

Andrew Yoon 3L

The electron that will removed is going to be from the last orbital of the element. Because this electron is furthest from the nucleus, it requires the least amount of energy to be removed. In order to find out which orbital the electron is being removed from, I would write out the electron configur...

Andrew Yoon 3L

To find the oxidation number of the example you gave, first you need to set up an equation. Since the final charge of the molecule is given (-1), we can set that equal to the charges of the Cl and O. -1 = (Cl) + 4(O). For O, we can assume it has a -2 charge. So then, we can solve the charge for Cl. ...

Andrew Yoon 3L

Hi, so for this problem, you have both structures correct. However for structure C, both O's (oxygens) should have a negative charge rather than C (carbon) having a negative charge. N (nitrogen) has the correct charge.

Andrew Yoon 3L

Electrons would be parallel when ground state electrons would fill two or more orbitals before pairing together in the same orbital. This means that the electrons in each orbital would have the same spin rather than when 2 electrons are in the same orbital and when they have opposite spins.

Andrew Yoon 3L

The second ionization energy is greater than the first ionization energy because there are less electrons in the element. With one less electron, the remaining electron(s) will face a greater attraction/pull from the nucleus of the element. In order to remove the second electron that is experiencing...

Andrew Yoon 3L

Yes, a triple bond is considered one sigma bond and two pi bonds right

Andrew Yoon 3L

Pi bonds only have p hybridization and not spx because they can only form with p orbitals.

Andrew Yoon 3L

Fluorine is the electronegative because it has 7 valence electrons. It only needs one more electron in order for it to have a noble gas configuration (electron octet). Therefore, it easily attracts electron and is highly reactive.

Andrew Yoon 3L

If your equation has any stoichiometric coefficients that are fractions, you need to convert them to whole numbers. Since you can't have a fraction of a compound, you need to multiply whatever number on one side to the other as well in order for it to be balanced.

Andrew Yoon 3L

For +1/2, I think it is supposed to represent spin up, and -1/2 is supposed to represent spin down.

Andrew Yoon 3L

All of the Sapling hw and chem community posts are due at Sunday night at 11:59 pm.

Andrew Yoon 3L

I think that those equations are derived from E = mc^2 and c = (λ)(v, frequency), P = (m)(v, velocity), and E = (h)(v, frequency)

Andrew Yoon 3L

For now, c will always be equal to the speed of light, which is 3x10^8 m/s.

Andrew Yoon 3L

The first step is to convert 3.39g of CuNO3 into moles. You can do this using the molar mass of CuNO3. Once you have converted the mass to moles, use the molarity equation (M = n/v) to solve for the volume. Make sure to convert to milliliters.

Andrew Yoon 3L

In this case, n=1 would be the final energy and n=2 would be the initial energy level. In order for it to be less confusing, you can replace n1 and n2 with nfinal and ninitial

Andrew Yoon 3L

No, Black Body radiation will not be on the midterm.

Andrew Yoon 3L

Amplitude is only used in the wave model. Increasing the amplitude means that there is a higher intensity. Decreasing the amplitude means that there is a lower intensity. With more a higher intensity, the brightness increases and vice versa. In order to change the energy, we have to change the frequ...

Andrew Yoon 3L

Hi, so for this question, you still use the equation (delta momentum)(delta position) > or equal to (h/4pi). However, for delta momentum, change the mass to helium. In order for helium to match with the units in the equation, first change the molar mass from g/mol to kg/mol. Next, multiply it my Avo...

Andrew Yoon 3L

There is an acronym:
King Henry Doesn’t Usually Drink Chocolate Milk

K- kilo
H- hecto
D- deca
U- base unit
D- deci
C- centi
M- milli

Andrew Yoon 3L

Once you have your answer, find the number with the least sig figs, and then apply the number of sig figs in that number to your answer.

Andrew Yoon 3L

I think the concept an how the equation is used is important for us and for the exam.

Andrew Yoon 3L

Hi! Yes, questions, comments, and replies are all counted as points. You need at least 5 of any of the three by Sunday at 11:59.

Andrew Yoon 3L

I would because it just gives you a lot of practice. Doing all the problems, is however, really hard to do.

Andrew Yoon 3L

To find the molecular formula, count the number of carbons, hydrogens, and oxygens, respectively. The order of the elements in the molecular should be CHO. Once you have found the number of each element (C6H8O6), you can find find the molecular mass of the compound. The molar mass of carbon, hydroge...

Andrew Yoon 3L

Hi!

Yeah I had the same problem too. What I suggest is to just go over the main chemical formulas (i.e. sulfide, bicarbonate, hydroxide, etc.). Those are kind of the basic formulas, but I don't think we are required to memorize anything more complicated than the examples.

Hope it helps!

Andrew Yoon 3L

The first step that I took to solve this problem was to figure out the mass of M. Since we know the mysterious compound has a molar mass of 74.10 g/mol and the molar mass of (OH)2, we can figure out the molar mass of M by subtracting 34.08 g/mol from 74.10 g/mol. This mass turns out to be 40.08g/mol...

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