CHEMISTRY COMMUNITY

Benjamin_Hugh_3F

The easiest way is just referring to the half-reactions sheet and finding the reactions including H+, OH-, and H2O. Otherwise, isolate the reactants H+ and OH- and write a half-reaction equation resulting in H2O by using O2 gas to balance the oxygen molecules. You can determine the anode and cathode...

Benjamin_Hugh_3F

Ea(forward)=Etransition−Ereactants

Ea(reverse)=Etransition−Eproducts

Thus, Ea(forward)−Ea(reverse)=Eproducts−Ereactants=ΔH

Just plug the values into the equation.

Benjamin_Hugh_3F

Use the integrated law for first-order reactions: [A]= [A]0 e^-kt.
Plugin the numbers and rearrange the equations to determine the t value.
The result will be in seconds, so convert it to minutes.

Benjamin_Hugh_3F

The cathode should be on the right and the anode should be on the left. But the electrodes do not have any order, so can be written in any form.

Benjamin_Hugh_3F

K = k1/k'1 = 265/392 = 0.676.

Benjamin_Hugh_3F

rate = k * 0.5[A] * (3*[B])^2
rate = 4.5 * k * [A] * [B]^2
rate = 4.5 * 0.0860

Benjamin_Hugh_3F

K = k(attach)/k(loss), thus, k(loss)=k(attach)/K

k(loss)=k(attach)/K= (7.4x10^7 L/mol^-s)/326 = 2.3x10^5 L/mol^-s.

Benjamin_Hugh_3F

I wish I could move in, but I'm in Korea, so I don't think I'll be going to the states anytime soon. Hope everyone stays safe!

Benjamin_Hugh_3F

The oxygen in the air reacts with the iron itself. The rust forms when the iron is exposed longer time to the water in presence of sun and air or in absence of sun. Forming the formula Fe2O3.nH2O.

Benjamin_Hugh_3F

a)Using stoichiometric relationships we know that 1 mole of A would form 3 moles of B. Hence forming 0.018 mol/L of B would mean the loss of 0.018/3= 0.006 mol/L of A. So the initial concentration of A is 0.015 mol/L and the concentration of A after 3 min is 0.015-0.006= 0.009mol/L. Thus k=(1/t)ln([...

Benjamin_Hugh_3F

A catalyst won't appear in the overall chemical equation as it isn't consumed during the reaction. But it can appear as a reactant in the rate-determining step.

Benjamin_Hugh_3F

A catalyst lowers the activation energy, and rate constants are dependent on the activation energy. Thus a catalyst affects the rate constants.

Benjamin_Hugh_3F

At equilibrium, the rate of forward reaction is equal to the rate of the reverse reaction. When molecules first begin to react, the rate of the forward reaction is faster than the reverse reaction. As reactants are consumed and products accumulate the rate of the forward reaction decreases, and the ...

Benjamin_Hugh_3F

Electrons always flow from the anode to the cathode. I'm pretty sure the anode is always on the left, and the cathode is always on the right.

Benjamin_Hugh_3F

Kinetics is related to the rate of reaction and thermodynamics decides on whether the reaction is favorable or not. So kinetic stability means that the reactant reacts at a slower rate. And thermodynamically stability depends on whether or not the reaction is spontaneous. So a thermodynamically stab...

Benjamin_Hugh_3F

Try starting off by utilizing the equation we learned. E°= RT/nF (lnK).

Benjamin_Hugh_3F

The x value is the time and the y value is the concentration. The graph shows us the rate of reaction.

Benjamin_Hugh_3F

I agree with Hannah. Electrons always flow from the anode to the cathode, so the anode should always be on the left, and the cathode should be on the right.

Benjamin_Hugh_3F

Yes, you have to use the given equation to determine the anode. pb4+ is on the right side of the half-reaction and the final equation, making it an anode.

Benjamin_Hugh_3F

Copper is a cation and chlorine is an anion. Thus, copper is oxidized and chlorine is reduced. In the compound CuCl, the ions are Cu+ and Cl− . Thus, the oxidation half‑reaction should contain Cu as the reactant and Cu+ as the product. It should also contain one electron on the more positive side to...

Benjamin_Hugh_3F

I'm also currently studying in Korea. For me, I think it helps a lot to watch the recorded classes because I tried taking classes live during midnight, but I wasn't able to focus, so if your classes are large classes and are recorded, just watch them during the afternoon in your timezone.

Benjamin_Hugh_3F

This is the sapling explanation. Assign the oxidation states to all species in the equation. In most compounds, oxygen has an oxidation state of −2 and hydrogen has an oxidation state of +1. The oxidation state of gold changes from 0 to +3, so it is oxidized. The oxidation state of nitrogen changes ...

Benjamin_Hugh_3F

I'll attach the step-by-step solution given by sapling. To begin, determine the oxidation numbers of each element in each half‑reaction. For the reduction step of the first reaction, the oxidation number of chlorine changes from +7 to+3 . Cl2O7⟶ClO−2 Next, balance the atoms of each half‑reaction. Ba...

Benjamin_Hugh_3F

The intensive property basically means that the standard reduction potential doesn't depend on how many times the reaction occurs. So the potential isn't multiplied by the integer used to balance the equation. An example that I found might help you understand the concept better. Imagine that you hav...

Benjamin_Hugh_3F

Determine which half cell is the anode and cathode. Then find the standard reduction potential for both zinc and silver from the list. Then use the equation E cell = E cathode − E anode to figure out the answer.

Benjamin_Hugh_3F

This is the explanation from sapling. In a galvanic cell oxidation occurs at the anode, so X is the anode. Reduction occurs at the cathode, so Y is the cathode. During oxidation, X loses electrons which travel away from the X electrode, through the wire to the Y electrode where they are gained by Y2...

Benjamin_Hugh_3F

An electrical potential is a measurement of the ability of a voltaic cell to produce an electric current. To get the maximum potential maximum amount of work has to be done so the lesser the current flows, the stronger the potential is.

Benjamin_Hugh_3F

When energy is released it is negative and when energy is absorbed it is positive.

Benjamin_Hugh_3F

https://chem.libretexts.org/
This is a website that I refer to a lot when I study.

Benjamin_Hugh_3F

These are some equations that come into my mind.

-ΔG∘r=ΣnΔG∘f(products)−ΣnΔG∘f(reactants)
-ΔS=nRlnV2/V1
-ΔST=CVln(T1/T2)

Benjamin_Hugh_3F

A larger disorder correlates to a higher ΔSvap, which means the molecules are more ordered in the liquid state. Thus high ΔSvap means molecules ordered liquid state and low ΔSvap means molecules are less ordered in liquid state.

Benjamin_Hugh_3F

The phase changes solid to liquid, liquid to gas, and solid to gas all have positive changes in entropy ( ΔS is positive). Liquid to solid, gas to liquid, and gas to solid all have negative changes in entropy ( ΔS is negative). The phase changes solid to liquid, liquid to gas, and solid to gas all h...

Benjamin_Hugh_3F

I'm not sure if we have the same sapling questions but based on my sapling #16, I am given a reaction equation to solve the delta G of the rxn. My equation is 6Cl2(g)+2Fe2O3(s)⟶4FeCl3(s)+3O2(g). All you have to do is refer to the standard energy of formation and plug it into the formula: ΔG∘rxn=ΣnΔG...

Benjamin_Hugh_3F

1. ΔG∘r=[ΔG∘f(C2H6(g))]−[ΔG∘f(C2H2(g))+2ΔG∘f(H2(g))]
2.Convert it to joules per mole
3.Set up the equation ΔG∘r = −(8.314Jmol⋅K)(25.0+273.15 K)ln(K)
4.Solve for K

Benjamin_Hugh_3F

It's just different expressions for volume units. 1L=1000ml=1000cm^3=1dm^3. They are all the same.

Benjamin_Hugh_3F

In a reversible process, if the external pressure increases infinitesimally, the piston moves inward, and if the pressure of the system increases infinitesimally, the piston moves outwards. If the external pressure is equal to that of the system, the piston doesn't move. In an irreversible process, ...

Benjamin_Hugh_3F

1. Yes first convert the watts to joules. 2. Then find the moles of molecules by finding the difference in the initial and final mass and dividing it by its molar mass. 3. Divide the energy(joules) by the moles to find the enthalpy of vaporization, and convert it to Kilojoules. 4. The molar entropy ...

Benjamin_Hugh_3F

The equation for the change in internal energy is ΔU=nCVΔT.
CV=Cp−R, so given that the Cp is 7R/2, 7R/2-R=5R/2.
Now plug everything into the first equation using the moles(0.305m), CV, and change in temperature(12.3K).

Benjamin_Hugh_3F

My sapling question is different from yours, but I believe the values of the standard enthalpy of formation you used are incorrect. Try checking the values again using this link https://sites.google.com/site/chempendix/thermo.

Benjamin_Hugh_3F

It's better to remember that the hydroxides of the Group I (alkali metals) and Group II (alkaline earth) metals usually are considered as strong bases. Ex)LiOH, NaOH, KOH, RbOH,CsOH, Ca(OH)2, Sr(OH)2, Ba(OH)2 But I found a mnemonic device on google if you need it. Li ttle Na nnies K ill R a b bits, ...

Benjamin_Hugh_3F

Yes, partial pressure is dependent on the mole of gasses in the container. You are also right with the question. When there is an increase in pressure, the equilibrium will shift towards the side of the reaction with fewer moles of gas.

Benjamin_Hugh_3F

If the question asks for the delta H you have to write the negative sign, but if it asks for how much KJ is released, I believe a sign wouldn't be necessary.

Benjamin_Hugh_3F

q refers to the amount of energy(heat) transfer, and Delta H refers to the change in enthalpy, basically referring to the state of the system.

Benjamin_Hugh_3F

The A decreases in the graph, which means it's a reactant, and B and C increase, which means they are products. A decreases by 10 pka, and B and C each increase by 5 and 10 pka. Thus the balanced equation would be 2A(g) --> 1B(g) + 2C(g).

Benjamin_Hugh_3F

Kw is an equilibrium constant, so it stays constant unless the temperature changes. If you increase [H+] or [OH-] the concentration of the other one will decrease and the Kw will equal to 10^-14 anytime.

Benjamin_Hugh_3F

Ka = [A⁻]·[H⁺]/[HA] =1.4 x 10^-6

[A⁻] = [H⁺] = x.
[HA] = 0.20M - x.

Ka= x²/(0.20M - x)

Solve for x to figure out [H+], then use the equation -log[H+] to solve the PH

Benjamin_Hugh_3F

We are given the PH(13.25), which means -log[H+]=13.25. Then [H+] would equal 10^-13.25( or 5.6 x 10^-14). Using that value you can find [OH-] in the diluted solution since Kw=[H+][OH-]=10^-14 After calculating [OH-], [OH-] x (500ml/5ml) would give you the concentration of [OH-] in the original solu...

Benjamin_Hugh_3F

If you solve the quadratic equation your x value should equal 0.00957... Try dividing that value by 0.1182M. You'll get a different answer. I think you got the wrong answer because you rounded up the x value.

Benjamin_Hugh_3F

Ka = [CH3CH(OH)COO-][H+]/[CH3CH(OH)COOH]= 8.40×10^-4 [CH3CH(OH)COO-] = x [ H+ ] = x [ CH3CH(OH)COOH] = 0.1048 - x From there you can find the value of x. If you know the x value you can figure out the PH using PH= -log[H+], and the POH accordingly. For the percent ionization divide [H+] by 0.1048M a...

Benjamin_Hugh_3F

The equilibrium isn't reached when the number of reactants and products are equal, but rather when the rate at which products are made is equal to the rate at which reactants are made. When the rate equals out, no more reactants or products are formed.

Benjamin_Hugh_3F

The equilibrium constant would be Kc=[HI]^2/[H2][I2].
When you express Kc in terms of x it would be 53.3=(2x)^2/(0.800-x)^2, which equals 7.30=2x/(0.800-x).
If you solve the equation x equals 0.628M.
Since [HI] is 2x, 2(0.628M) will result in 1.256M.

Benjamin_Hugh_3F

I think you're right on this question. SF4 is a non-polar molecule with a see-saw shape.

Benjamin_Hugh_3F

Although XeF2 has 3 electron pairs because it is arranged symmetrically around Xe, so the bond angles will still be 180 degrees, making the molecule linear.

Benjamin_Hugh_3F

I agree with you that b and c are non-polar and a and d are polar molecules. Maybe the answer key is wrong?

Benjamin_Hugh_3F

I hope everyone does well on the test and has a happy winter break!! Good luck :)

Benjamin_Hugh_3F

The Arrhenius Theory states that acids are substances that produce hydrogen ions in solution and bases are substances that produce hydroxide ions. The Bronsted Lowry Theory states that acid is a proton donor and base is a proton acceptor. The Lewis Theory says that acids act as electron-pair accepto...

Benjamin_Hugh_3F

By definition, strong acids and bases completely dissociate and weak acids and bases partially dissociate. But I think you should just memorize it.

Benjamin_Hugh_3F

Well by definition, atoms that donate protons are acids, and atoms that accept protons are bases. So in the balanced equation, identify the number of hydrogens that increased or decreased. If it decreases, it means it is a Brønsted acid, and if it increased it means it is a Brønsted base.

Benjamin_Hugh_3F

I am also slightly confused because HF is known to be a weak acid, but sharing my second thought if we look at it from a relation between acid and conjugate base, a stable(weaker) conjugate base means it has a strong acid. If you look at the equation: HF + H20 --> F- + H30+, F- is a stable conjugate...

Benjamin_Hugh_3F

Salts formed by weak acid and base hydrolyzes just like the strong base/weak acid and strong acid/weak base reaction, but whether or not it creates an acid or base depends on whichever the acid or base is stronger. The dominant factor will determine whether it is acidic or basic.

Benjamin_Hugh_3F

C6H5NH3+ is a weak acid so it will give away a proton when it reacts with H2O, creating the equation: C6H5NH3+ + H20 -> H3O+ + C6H5NH2.

Benjamin_Hugh_3F

Looking at the PH equation will help you understand why pH<pKa means a solution is acidic.
pH=pKa+log([A−]/[HA])
If the pH is lowered so that it is lower than the pKa, then it means HA should be greater than A-, making the solution more acidic.

Benjamin_Hugh_3F

H2PO4- can act as a proton donor to a water molecule, showing its acidic character. (Conjugate base: HPO42-)

: 8757-15-39E-i4.png (3.86 KiB) Viewed 102 times

It can also accept a proton from HCl, showing its basic character. (Conjugate acid: H3PO4)

: 8757-15-39E-i6.png (3.61 KiB) Viewed 102 times

Benjamin_Hugh_3F

This chart may help you understand the relation between hybridization and molecular shape.

Benjamin_Hugh_3F

As Dr. Lavelle said in the email the test will be approximately weighted to the amount of time covered in the syllabus, so I think I'll be focusing more on the Quantum sessions.

Benjamin_Hugh_3F

I'm pretty sure each session will be covering the same topics, but since it's held by different TA's, the way they deliver the materials might be slightly different.

Benjamin_Hugh_3F

Resonance can lead to the delocalization of the electron pair in the base, which increases the stability. A weaker base means it has a stronger conjugate acid; thus, an acid with a delocalized conjugate base means it is acidic.

Benjamin_Hugh_3F

A conjugate acid and base are basically two substances that differ only by one proton (H⁺). A conjugate acid is formed when a proton is added to a base, and a conjugate base is formed when a proton is removed from an acid. The following images are examples of conjugate acid-base pairs.

Benjamin_Hugh_3F

I think you're right about writing diaqua before bisoxalato because as long as I know the name should be alphabetized according to the actual ligand name, instead of the prefixes.

Benjamin_Hugh_3F

An acid is a substance that donates protons following the Bronsted Lowry definition or it can also be said as a substance that accepts a pair of valence electrons to form a bond following the lewis definition. Both definitions essentially create an negative charge. A base is a substance that can acc...

Benjamin_Hugh_3F

Just to clarify, the coordination number is basically equal to the number of ligands attached to the central atom, not the total number of ligands right?

Benjamin_Hugh_3F

I think it's a nomenclature to use the Latin name(Ferrate) when naming a coordination compound.

Benjamin_Hugh_3F

The lone pairs react with the bonding pairs at an angle of 90 degrees. In the T-shape, there will be 4 lp/bp interactions, but in the case of a trigonal planar shape, when the lone pairs are placed at the top and bottom, the lone pairs will result in 6 lp/bp interactions, which causes more repulsion...

Benjamin_Hugh_3F

It's on a different date, but the process such as zoom proctoring and using the lockdown browser will be the same right?

Benjamin_Hugh_3F

I haven't seen my family for 5 months cause the border is blocked, but I at least went skiing with my friends which were pretty fun.

Benjamin_Hugh_3F

Ligand is "an ion or molecule attached to a metal atom by coordinate bonding." And a neutral ligand basically means a chargeless ligand. Common examples of it include H20, CO, NH3, and C2H4.

Benjamin_Hugh_3F

The true bond length will be the average of all resonance structures since they act as the same molecule's contributing structures. To determine which resonance structure contributes the most, you need to compare the formal charge. The structure with the least number of formal charges will be more s...

Benjamin_Hugh_3F

Dipole simply means a pair of equal and opposite electric charges separated by a small distance. Whereas the dipole moment is the strength of the dipole.

Benjamin_Hugh_3F

As long as I know, it's the date written on MyUCLA, but it says that check back on 11/30/2020 for the exam location, so I guess we'll receive an email soon regarding the exam.

Benjamin_Hugh_3F

I think it depends on what the questions ask for, but at least in high school, as long as our answers were in a certain range, it was fine. However, I still think It's always better to just memorize the exact/approx values just in case.

Benjamin_Hugh_3F

I think it was better than the first test, but I'm not that confident either. You'll definitely pass so don't worry too much about it!!!

Benjamin_Hugh_3F

Not having a double bond doesn't mean there isn't a resonance structure. As long as, 1.The overall charge of the system remains the same, 2.The bonding structure is the same(single, double, triple bonds can be different) 3.The structure follows the rules of lewis structure 4.The same molecular formu...

Benjamin_Hugh_3F

I'm guessing no because chemical bonding requires the transfer of energy; however, although atoms do have zero-point energy(vibration), I don't think the molecular motion can transfer the energy to another atom.

Benjamin_Hugh_3F

I'm pretty sure we're going to be given the molecular formula just like the question in Sapling. If not, an example structure for questions such as drawing resonance structures.

Benjamin_Hugh_3F

The structure with a lower formal charge is more preferred. In the first structure of a, the formal charge of all three atoms is 0, but in the second structure, Xe's formal charge is -1, and the F on the right is +1, making the first structure more dominant. Similarly, in the first structure of b, t...

Benjamin_Hugh_3F

The electron configuration is actually [Ar] 3d10 4s2 4p1. I believe the reason why Ga3+ is preferred over Ga+ is that removing 3 electrons will give Gallium a full shell, making it more stable.

Benjamin_Hugh_3F

The dipole-dipole interactions come from the c-cl bond because the cl's are arranged asymmetrically, creating a net-dipole. C will have the positive charge and Cl will have the negative charge.

Benjamin_Hugh_3F

As long as I know the total # of resonance structures can only be determined through drawing it out. For the structure between carbon and nitrogen, as long as the structure has the same molecular formula, the total number of electrons (same overall charge), and the same atoms connected together, it ...

Benjamin_Hugh_3F

The electrons in the 2s orbital has more density near the nucleus than the 2p electrons so the orbital energy becomes negative. The 2p electrons are shielded by the 2s orbital; thus, has higher energy. Also referring to the quantum number, l=0 for the 2s orbital and l=1 for the 2p orbital, so 2p ele...

Benjamin_Hugh_3F

Ionization energy can be measured in other states, but the reason why it is measured in a gaseous state is that there is less attraction between the other particles that can affect the ionization energy. If the IE was measured in a solid-state, the intermolecular forces can deceive the value as the ...

Benjamin_Hugh_3F

The major examples are chromium and copper. According to the Aufbau principle, the electron configuration of chromium should be [Ar] 3d4 4s2, and copper should be [Ar] 3d9 4s2. However, in reality, it is [Ar] 3d5 4s1 and [Ar] 3d10 4s1. This is because a half-filled or completely full d-subshell is m...

Benjamin_Hugh_3F

Atoms have a tendency to either form a full octet or a half-filled octet. Fluorine has 7 electrons in the outer shell, nearly achieving a full octet, and it has a higher nuclear charge, making it hard to remove the electrons. On the other hand, Oxygen has 1 more electron in the 2p orbital than the h...

Benjamin_Hugh_3F

It refers to the effective nuclear charge, so if an electron has a more effective nuclear charge than others, it means it causes greater attraction, pulling the electrons closer to the nucleus.

Benjamin_Hugh_3F

Sulfur has an expanded octet, allowing it to occupy its empty 3d orbitals. Because it has 6 unpaired electrons, it can form 6 covalent bonds, allowing it to have 12 valence electrons.

Benjamin_Hugh_3F

Honestly, it's not that easy to fully get rid of your anxiety. Consider the test as another sapling assignment. You'll feel less pressured. Study hard for a couple of hours and take a break by listening to music or watching Netflix. Personally, this helps me a lot because it stops me from consistent...

Benjamin_Hugh_3F

As explained in the solution in Sapling, the formal charge of the central atom that matches the oxidation number most closely is the most plausible structure. For example, in question 9, the Cl atom from structure E has a formal charge of 3+, which is the closest to the oxidation number of +7; thus ...

Benjamin_Hugh_3F

I think you already have the idea, but just to clarify, the atomic radius decreases across the period and down the group, so the attraction of the nucleus and electrons are stronger, causing the atoms to be more compact, which increases the Zeff. Zeff is the effective nuclear charge, so the ionizati...

Benjamin_Hugh_3F

I believe H2SeO4 has a dipole-dipole force due to the asymmetry of Se since the O has a higher electronegativity than Se, which leads to the greater pulling of electrons. Being more electronegative means more electrons are attracted to that atom, so I'm assuming that the Oxygen region is more negati...

Benjamin_Hugh_3F

Adding on, electronegativity can also affect the bond length. The higher the electronegativity, the stronger the electrons will be pulled toward the atom. Which will lead to a shorter bond length since it's harder to separate the electrons from the atom. I guess this is just another way to explain b...

Benjamin_Hugh_3F

O has an ionization of 1314, and Cl has 1251. The two elements are close to each other, so it may be a little confusing to conclude exactly by looking at the periodic table, but I think if there's a question on ionization energy, we would be given a chart with the energies listed on it.

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