CHEMISTRY COMMUNITY

Seohyun Park 1L

What is the difference between activation energy and free energy of activation?

Seohyun Park 1L

Does the rate law of a reaction give the unique rate?
If so, how do you know if a question is asking you to find the rate law, or specifically the rate of formation of a product/reactant?

Seohyun Park 1L

Pre equilbirum approach is usually used when the slow step has an intermediate in its rate law, so mostly entirely in the case that you mentioned with a fast step first and then a slow step after. If the first step is the slow test, the pre- equilibrium approach is most likely not needed.

Seohyun Park 1L

Cell Potential changes depend on Q (concentration of products/reactants) as the reaction is always going to proceed towards equilibrium (K). So as Q gets closer to K, the cell potential will decrease as the reaction is closer to equilibrium. Standard cell potential is in the situation when the cell ...

Seohyun Park 1L

If a graph of the reaction is given in terms of progress v. energy, it would be the Activation energy of the forward endothermic reaction minus the enthalpy difference of the forward reaction.

Seohyun Park 1L

The integrated rate laws are given on the formula sheet, so you wouldn't need to know the exact derivations.

Seohyun Park 1L

Both equations are technically the same but due to rounding lead to slightly different answers. I personally just use the ln equation as the original equation is with ln.

Seohyun Park 1L

The definition of E standard is assuming that the concentrations in both cells is 1M. So if the concentrations on the cells are different, the E standard is still 0 seeing that the species are the same and they are both in 1M, but the E value would be different as they are not under standard conditi...

Seohyun Park 1L

Can liquids conduct electricity and act as cathode/anode? For example, in one of the textbook problems Hg(l) acts as an anode and there is no inert metal like platinum.

Seohyun Park 1L

You can use Van't Hoff equation to find K based on changing temperature but you can only do it in cases where you can assume entropy and enthalpy stays constant.

Seohyun Park 1L

Why is E standard a intensive property? What about E standard causes it to not change even when concentration changes?

Seohyun Park 1L

When writing cell diagrams and you use commas (when the components are in the same phase), does the order matter? For example, is there a difference between Cu2+ (aq), Cu4+ (aq) and Cu4+ (aq), Cu2+ (aq)?

Seohyun Park 1L

Why does the free energy of a reaction (not the standard free energy) depend on the pressure and equilibrium constant?

Seohyun Park 1L

The "m" in Sm stands for molar, so Sm means molar entropy.

Seohyun Park 1L

Delta H negative does not always mean a spontaneous reaction as entropy plays a part. If the entropy of the system decreases and the temperature is high enough, an exothermic reaction could be non spontaneous as the TOTAL entropy (entropy of system + surroundings) is decreasing.

Seohyun Park 1L

In irreversible expansions, will the internal pressure of the gas in the container be equal to the external pressure at the end of the expansion?

Seohyun Park 1L

Theoretically, every step would be in equilibrium, which makes it reversible not irreversible.

Seohyun Park 1L

Entropy change through heating curve is similar to that of calculating enthalpy change. For phase changes, you would use Delta S= qrev/T as temperature is constant. You can calculate qrev using the enthalpy of fusion/vaporization/whatever situation is. For temperature changes, you would use Delta S=...

Seohyun Park 1L

Why do molecules with higher molecular weight (not the number of bonds) have higher standard molar entropies? Does it have to do with vibrations of the particles?

Seohyun Park 1L

Why is the total entropy change equal to 0 in a reversible, isothermal gas expansion?

Seohyun Park 1L

Is a constant pressure calorimeter considered an open or isolated system?

Seohyun Park 1L

For enthalpies of reaction (both standard and not), do you use kJ or kJ/mol? It seems like in the textbook problems many times there are used interchangeably.

Seohyun Park 1L

I'm assuming you do assume w=0 because the only work we consider in reactions is usually pressure-volume expansion and in constant volume, delta v= 0.

Seohyun Park 1L

Besides by looking at the graph of reversible v. irreversible expansions and seeing that the area of work done is greater for reversible expansions, what explains the fact (more theoretical explanation) that reversible expansions do more work than irreversible expansions?

Seohyun Park 1L

Enthalpy of reaction is how much heat (at constant pressure) the reaction absorbs or gives off (so a more general concept/term). Enthalpy of reaction is how much heat a reaction absorbs/gives off when a compound is formed from its constituent standard elements. An example of this would be the change...

Seohyun Park 1L

Why is Cp for a gas greater than Cv?

Seohyun Park 1L

What exactly is the difference between heat and enthalpy? I know that heat is pathway dependent and enthalpy is a state function, and that the heat released/gained in reaction at constant pressure is the Delta H. But what makes q a pathway dependent state? What makes the heat released/gained at diff...

Seohyun Park 1L

When a problem asks for the pH of the solution, should you round the concentration for H+ to its proper sig figs before finding the pH (then rounding to its sig figs again)? I remember Dr. Lavelle mentioning not to round until the very last answer, but in the textbook solutions, they end up rounding...

Seohyun Park 1L

For me, I memorized the list of strong acids (7 or so please double check) and strong bases ( group 1 and group 2 hydroxides and oxides). The rest are usually weak acids and bases.

Seohyun Park 1L

ICE tables are only used to find concentrations at equilibrium and thus is related to K. Q gives ratios of the concentrations of products/reactants not at equilibrium.

Seohyun Park 1L

I believe you can use either. I would say use the units it gives in the problem? I don't think I encountered problems in the textbook that gave different units for gases.

Seohyun Park 1L

Does the 5% Rule for approximation only apply to acid/base reactions in water? Can we use the approximation technique for small K values for equilibrium problems not involving acid/base?

Seohyun Park 1L

When someone increases the partial pressure of one particular gas when there are multiple gases, is it implied that the person is adding more moles of the gas? Or is there another method?

Seohyun Park 1L

You would use ICE tables to find the appropiate equilbirum concentrations of Cl2 and F2 and the K values are in the textbooks. For part C, you can compare K values or compare concentration values to see whether Cl2 or F2 separates less, leading for it to be more "stable."

Seohyun Park 1L

Can we use values with both atm and bar in Kp for gases (not in the same calculation, but separately)? For example, if the problem gives gas pressure values in atm, we wouldn't need to convert to bar?

Seohyun Park 1L

Will a chemical reaction within a system always head towards equilibrium, no matter the concentration of the reactants? If a reaction does always go to equilibrium, why do we say some reactions go to completion then?

Seohyun Park 1L

I used an ICE table for that problem as it helps you see how much NH3 was formed in comparison to CO2. You don't need the value of NH4NH2CO2 in the problem because it's not involved in the equilibrium constant equation as it is a solid.

Seohyun Park 1L

You can use either, but sometimes they state explicitly to find Kc (concentration) or Kp (pressure) or they give the equilibrium constant in those two forms. If they give Kc, you have to use concentration and if they give Kp you have to use pressure.

Seohyun Park 1L

Amphiprotic refers to a compound that can accept or lose a proton. Polyprotic acids refers acids that has multiple protons it can lose in an acid-base reaction (for example H2SO4, H3PO4)

Seohyun Park 1L

A ligand is neutral if it has no charge. NH3 would be a neutral ligand while Cl- would not as it has an overall negative charge.

Seohyun Park 1L

When H20 is a ligand of a coordination compound, is it written as OH2 or H2O in the chemical formula? The solution manual seems to be inconsistent the method white textbook says OH2.

Seohyun Park 1L

An example would be a water molecule interacting with O2. The dipole moment between the O and H in water will cause the nonpolar bond between the two oxygens in O2 to have a instantaneous dipole moment with one side having a slight positive charge and the other side having a slight negative one.

Seohyun Park 1L

I think VSEPR always considers molecule with one central atom and names the structure based on the number of lone pair electrons and bonded electrons of the central atom. However, I'm not sure about the case for I3.

Seohyun Park 1L

Hybrid orbitals can only make up sigma bonds as pi bonds are only between p-orbitals

Seohyun Park 1L

Why is intermolecular energy described as negative?

Seohyun Park 1L

In HW problem 4.81 for 6th edition, the structure B3N3H6 (borazine) has both double bonds between N and B and single bonds between N and B in a hexagonal shape (similar to Benzene). How is possible that boron can form a pi bond along with 3 sigma bonds (two with N, one with h) when it only has 3 val...

Seohyun Park 1L

For trigonal bipyramidal electron structures, I know that for AX4E (seesaw) molecular structure, the lone pair is located on the equatorial plane with the trigonal planar structure because it "affects/repels less electrons." Why is that the lone pair in the equatorial plane affects less el...

Seohyun Park 1L

Double bond is basically a sigma bond and pi bond. The sigma bond is usually a hybridized orbital but pi bonds can only be between p orbitals, and not between hybridized orbitals.

Seohyun Park 1L

Why is it that AX2E3 has a linear shape even with a trigonal bipyramidal electron geometry? Wouldn't the 3 lone electron pairs have an effect on the shape?

Seohyun Park 1L

Can someone explain what E directly relating to polarizability and indirectly relating to radius means for instantaneous interactions? What is the energy referring to in this case?

Seohyun Park 1L

Why is it that a shape with the least amount of repulsion is the most stable? Don't the electron pairs want to be as far away from each other as possible?

Seohyun Park 1L

The elements that can have more than 8 valence electrons have orbitals principal quantum number of at least 3 (n=3) so they have access to the d orbitals (d orbitals only start appearing from n=3). So, they can put the extra electrons in the d orbital. This explains why oxygen and nitrogen are not a...

Seohyun Park 1L

What exactly is the difference between polarizability and electronegativity? I know electronegativity is the pull of electrons and is the cause of dipole moments, but is polarizability only relevant in the induced dipole-induced dipole intermolecular force?

Seohyun Park 1L

Technically, intermolecular forces (ion-dipole, dipole-dipole, dispersion) occur between molecules and compounds, and not between bonds within the compound itself. Hydrogen bonding is a type of dipole dipole. And dispersion forces are present for all interactions between molecules. For ionic, I'm as...

Seohyun Park 1L

Problem 3.57 in the 6th edition asks for the lewis structure for hydrogen sulfide HSO3-. How do you know that the H is bonded to one of the oxygens? I drew the lewis structure so the H is bonded to S (the central atom) and worked out formal charges to seemingly make it work but the solutions manual ...

Seohyun Park 1L

Conceptually, why is energy released when an atom gains an electron? I understand that it takes energy to remove an electron (ionization energy), so the other way around would release energy, but is there another explanation?

Seohyun Park 1L

Most likely atomic radius, ionization energy, electron affinity, and electronegativity. You will probably also need to know the trends for ionic radii.

Seohyun Park 1L

The number of nodal planes matches the number of the angular momentum quantum number. For example, s has 0 (l=0) and p has 1 (l=1) and d has 2 (l=2) (technically only 4 out of 5 but the pattern remains essentially same). You can see this in the shape of the orbital itself as the p orbital has one po...

Seohyun Park 1L

What exactly is the definition of resonance? Is it the fact that molecules can have multiple lewis structures or the fact that electrons are delocalized and there is a "blending of structures"?

Seohyun Park 1L

Since the light emits 11J of total energy, you would divide 11J by the energy of one photon to find the total number of photons involved.

Seohyun Park 1L

The energy of the photon is equal to the energy required to remove an electron from the metal PLUS the kinetic energy of the removed electron. Since the electron removed in the problem has that given kinetic energy, you have to take into account both the kinetic energy of the electron AND the work f...

Seohyun Park 1L

You would have to add the E given the frequency to the energy level for n=4. Using that new E value, you would plug it in the E=-hR/n^2 to find the n value for the energy level for n2.

Seohyun Park 1L

For 6th edition, 1.15, the problem asks to find the principal quantum number of a certain wavelength. Using Rydberg formula, I was able to find the right value of n2 assuming n1=1, but when I tried using E=-hR/n^2 and subtracting the energy level for n1 from n2, I failed to get the right n2 value. I...

Seohyun Park 1L

Conceptually, why is it that the more precisely you measure the position of an object, the less precisely you can measure the momentum for the Heisenberg Indeterminacy Equation?

Seohyun Park 1L

Since you are detecting the light that is absorbed by the substance, the spectrum would be an absorption spectrum as you are seeing which wavelengths of light are being absorbed (hence the name absorption spectroscopy). If you were detecting the light emitted by a substance, then it would be the emi...

Seohyun Park 1L

For 1.33 (6th edition), part a asks for the wavelength an electron gives off given its velocity. First, I used wavelength = h/p (de borglie equation) to find the right answer. I tried a different method using the given velocity to find its kinetic energy (KE= 1/2mv^2) , and plugged that into E=h(fre...

Seohyun Park 1L

If a light has a long wavelength, it has a small frequency. The energy per photon is determined by E = hv (with v being frequency and h is Plank's constant). Small frequency means less energy per photon, making the photon not have enough energy to remove the electron from the metal.

Seohyun Park 1L

You basically need to find the amount of P4O6 produced from the first reaction. Then, you would find out how much P4O6 is consumed with the O2 in the second reaction. Subtract the P4O6 consumed from the P4O6 used in the first reaction, and you would have the mass of the excess reactant.

Seohyun Park 1L

Basically, the photoelectric effect showed that the wave model was not enough to describe the characteristic of light. If light was only a wave, increasing the intensity of the light, no matter what wavelength, would have gotten the electrons out (because for waves higher intensity --> more energy -...

Seohyun Park 1L

200. would be 3 sig figs and 200.0 would be 4 sig figs so they would be different

Seohyun Park 1L

The 40.48 g/mol is for the metal of the compound (which is Ca). If you take the sulfide of Ca, it would be CaS, so you would need to add the molar mass of sulfur to the molar mass of Ca, getting a final answer of 72.15 g/mol.

Seohyun Park 1L

Since it's asking for moles and you're given number of atoms, it's like you said how you just need to divide by Avogadro's number

Seohyun Park 1L

If the problem doesn't specify, mass percent composition refers to finding it for all the elements (in this case C, O, N, H)

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