CHEMISTRY COMMUNITY

Robert Tran 1B

Either way works, but the reaction is written with the fraction so that the coefficient of the product is one.

Robert Tran 1B

A catalyst is present in the beginning, while an intermediate is only present in the steps in the middle of the reaction process.

Robert Tran 1B

Molecularity is the amount of species that interact with each other as reactants.

Robert Tran 1B

Will there be a livestream option for the review session with classes being cancelled?

Robert Tran 1B

Why doesn't a catalyst affect the equilibrium position of a reaction?

Robert Tran 1B

For all conditions, the slowest step determines the rate of the reaction, because the reaction can only proceed as fast as the slowest process.

Robert Tran 1B

No, since the concentration is so high, it stays almost exactly the same, so it does not need to be included.

Robert Tran 1B

A catalyst changes the intermediates of a reaction so that the mechanism has a lower activation energy.

Robert Tran 1B

An integrated rate law shows the concentration of a substance at a certain point in time. The rate law only shows the change in concentration.

Robert Tran 1B

If the Ecell is the same, the substance that is oxidized/reduced will depend on the concentration. The substance in lower concentration will be oxidized, while the substance present in higher concentration will usually be reduced.

Robert Tran 1B

In addition to what has already been said, for a reversible expansion, there is heat transfer to maintain the temperature. However, for an irreversible expansion, there is no heat transfer because the change occurs too quickly.

Robert Tran 1B

No, since third order reactions are very uncommon, they are not covered in our curriculum.

Robert Tran 1B

The activation energy is the amount of energy that is required initially for a reaction to occur. This value is important because it determines how likely a reaction is to occur, and therefore, how long it will take to occur.

Robert Tran 1B

Since (delta)G in the Appendix is only for 25 C, we must calculate (delta)G using H and S to find it at 150 C.

Robert Tran 1B

It is Ecell because this value depends on the reaction quotient.

Robert Tran 1B

When you add the half reactions together, you get a coefficient of 2 in front of every reactant and product. In the dissociation reaction, the stoichiometric coefficients are 1. Thus, in order for the Ka to correspond to a stoichiometric coefficient of 1, we must square root the K value.

Robert Tran 1B

What's the difference between cell potential and standard cell potential?

Robert Tran 1B

When there is an acidic solution, you use H+ to balance out the hydrogen atoms. On the other hand, for a basic solution, you use OH- to balance out the hydrogen atoms.

Robert Tran 1B

Could someone explain conceptually why the gibbs free energy depends on the reaction quotient Q?

Robert Tran 1B

When we calculate cell potential, do we always subtract the potential of the right cell by that of the left cell?

Robert Tran 1B

Look at the balanced half reactions and determine how many electrons are being transferred in the redox reaction.

Robert Tran 1B

Another way to see cell potential is the potential of the cell to do work. If there is a greater difference between the concentrations of the reactants in a spontaneous reaction, it will be able to do more work.

Robert Tran 1B

Although iodine is a solid, it is not a conductor. Thus, we need to put a conducting metal (platinum) in order for the reaction to occur.

Robert Tran 1B

If the voltage of the cell is negative, then the cell does not have a spontaneous reaction in the specified direction.

Robert Tran 1B

The posts are usually counted at the end of the quarter. You should do 5/week to stay on track, but as long as you have 50 by the end of the quarter and you didn't do a bunch of them at the same time, you'll be good.

Robert Tran 1B

The salt bridge ensures that the solution in the anode and the cathode stays neutral. Since electrons are being transferred as the redox reaction occurs, the charges of the anode and the cathode are changing. The salt bridge dispenses ions as they change to ensure that there is no polarization that ...

Robert Tran 1B

The change in entropy is zero because the final state of the system is the same as the initial state. Since entropy is a state function and there is no overall change in the conditions, the entropy does not change.

Robert Tran 1B

So far in the course, the only form of work we have learned is the system expanding and pushing against the surroundings.

Robert Tran 1B

I also got pH = 4.545!

Robert Tran 1B

nRln(V2/V1) only works when the temperature is constant because it is derived from the equation (delta)S = q/T, which assumes that temperature is constant.

Robert Tran 1B

During a reversible expansion, the change in volume is slow enough that the temperature can stay constant. However, in an irreversible change, the process occurs too quickly to keep the temperature constant.

Robert Tran 1B

Since HA is a weak acid, it will not completely dissociate into H3O+ ions. This means that the initial concentration of HA will not be the same as the final concentration of H3O+ ions.

Robert Tran 1B

Work will be negative if the volume is increasing. You should always keep the negative if you are calculating the work being done on the system.

Robert Tran 1B

I noticed one of the practice problems wrote entropy as ΔS_m. Does anyone know what the "m" stands for in this term?

Robert Tran 1B

What is residual entropy and how does it arise?

Robert Tran 1B

A microstate is a possible arrangement of molecules in a given space. If there are more degenerate microstates, meaning that they all have the same energy, then the entropy is higher.

Robert Tran 1B

If C is not given in the problem, you can use the equation Cv = (delta)U/(delta)t or Cp = (delta)H/(delta)T.

Robert Tran 1B

I understand how the equation (delta)S = (delta)H/T is mathematically derived, but I don't understand conceptually why it makes sense that change in enthalpy, temperature, and change in entropy can be related to each other. Does anyone have an explanation?

Robert Tran 1B

If multiple reactions are given, the Hess's Law should be applied. If one reaction and the standard enthalpies of formation are given, then you should subtract the standard enthalpies of formation of the products by that of the reactants.

Robert Tran 1B

Since this chapter mostly deals with changes in temperatures, it does not matter whether Kelvins or Celsius are used because they are scaled the same.

Robert Tran 1B

Closed systems can exchange energy with their surroundings. On the other hand, isolated systems cannot exchange energy with its surroundings. This means that closed systems can transfer heat, but isolated systems cannot.

Robert Tran 1B

What is the meaning of a reversible process and what are the implications of it having an infinitesimal changes?

Robert Tran 1B

The standard enthalpy of formation should be multiplied by the amount of moles reacted.

Robert Tran 1B

In addition to what was already said, an amphiprotic substance is always amphoteric. However, an amphoteric compound is not always amphiprotic.

Robert Tran 1B

Yes, because steam must lose energy to convert into a liquid when it condenses on your skin. This is in addition to the heat released by the temperature change in the water when it touches your skin, which would be the only source of heat for a liquid burn.

Robert Tran 1B

Pickup is at the mailing center in Young Hall. Be sure to bring your BruinCard or some form of ID when you pick it up.

Robert Tran 1B

The SI unit is kJ/mol.

Robert Tran 1B

In an endothermic reaction, the reaction removes heat from the surroundings. In an exothermic reaction, the reaction adds heat to the surroundings. However, all reactions take some heat to begin (activation energy), so the previous statements are based on net changes.

Robert Tran 1B

Since Al(3+) is a small, highly charged cation, it can act as an acid when it is a hydrate in the form Al(H2O)₆³⁺. The Ka value for this can be found in the text.

Robert Tran 1B

Has anyone seen homework problems that have to do with buffers? Also, will it be on the test this week?

Robert Tran 1B

When the pressure increases, the reaction will shift to the side that produces less moles of gas. Conversely, when the pressure decreases, the reaction will shift to the side that produces more moles of gas.

Robert Tran 1B

You should use the R constant that has units that cancel out with the other units in the equation. For example, in PV=nRT, we use 0.08206 (L*atm)/(mol*K) because it cancels with the pressure, volume, moles, and temperature.

Robert Tran 1B

The equilibrium will shift towards the right. This is because endothermic reactions take up heat, so forming more products would lessen the effect of the increase in temperature.

Robert Tran 1B

If the percent deprotonation is less that 5%, then when we calculate equilibrium concentrations, we can ignore the x values relative to the initial concentration because it is not significant.

Robert Tran 1B

Yes, because in a chemical equation, the products are on the right side. Thus, a shift to the right means more products will form.

Robert Tran 1B

Both the K constant and the initial concentrations should be used when calculating sig figs because they are both used in the overall calculation.

Robert Tran 1B

Kc is calculated when the reaction is at equilibrium. On the other hand, Q is calculated when the reaction is at any other state.

Robert Tran 1B

If the K value is large, the reaction favors the products. On the other hand, if the K value is small, the reaction favors the reactants.

Robert Tran 1B

The ideal gas law can be used to solve for pressure, volume, temperature, and amount of moles. In class, we also used it to convert from partial pressure to concentration and vice versa.

Robert Tran 1B

Maggie Eberhardt - 2H wrote:Sorry if this is a stupid question, but when/why do we use ICE table?

We use an ICE table when we are given the initial concentration and want to determine the final concentration values after equilibrium is reached.

Robert Tran 1B

Since pH uses a log scale, the initial molar concentration does not matter. To answer this problem, you can use any arbitrary value for the initial molarity and get the same answer.

Robert Tran 1B

Question 9C.5 part b asks how many places (CO3)2- can bind to a single metal center. The answer says that it can be mono or bidentate. Why can it be both?

Robert Tran 1B

pH values are not solely confined to the values 0-14. However, most solutions fall within this range.

Robert Tran 1B

This is likely not a typo, because the triple equal sign means "is equivalent to," which is more specific than "is equal to."

Robert Tran 1B

The hydrogen ion is often used in place of hydronium to simplify things. However, you should know that the hydronium ion better represents what is actually seen.

Robert Tran 1B

Cisplatin stops DNA replication by bonding to two exposed guanines. This prevents the enzymes from replicating the DNA. Transplatin does not stop DNA replication because its shape only allows it to bind to one guanine. This bond is not strong enough to prevent replication.

Robert Tran 1B

There isn't a clear definition for acids, just different theories. Thus, we have different classifications such as Bronsted and Lewis.

Robert Tran 1B

EDTA can remove harmful metals such as lead from the body because it is able to bind to the metals.

Robert Tran 1B

O2 is nonpolar because there is no difference in electronegativity, and therefore, no dipole moment between the atoms.

Robert Tran 1B

Bent and angular mean the same thing. There are also several names for other structures, such as seesaw (disphenoidal).

Robert Tran 1B

The bond angle will be less than expected if there is a lone pair present, because the electron-electron repulsions will push the bonds closer together.

Robert Tran 1B

A linear bond can be polar if the dipole moments are unequal, and therefore, do not cancel out.

Robert Tran 1B

Hybridization will not be tested on Test 2. Only content from after the midterm to sigma and pi bonds will be tested.

Robert Tran 1B

Oxygen can have all types of bonds, but it usually does not have triple bonds because the formal charge of oxygen would be more likely to have a nonzero value. This is because oxygen has 6 valence electrons and a triple bond would cause the formal charge to usually be 1.

Robert Tran 1B

Radicals are highly reactive because they have one unpaired electron. Antioxidants prevent them from reacting by donating an electron to make an electron pair.

Robert Tran 1B

Only sigma and pi bonds from today's lecture will be covered on Test 2.

Robert Tran 1B

A is the central atom, X is the amount of bonded atoms, and E is the amount of lone pair electrons.

Robert Tran 1B

Since the S--F bond has a dipole moment and the seesaw shape does not allow the dipole moments to cancel out, the molecule is polar. If all the bonds were arranged symmetrically, in a tetrahedral shape, for example, the molecule would not be polar.

Robert Tran 1B

There's no curve for the midterm, but if the average grade is low enough, there will be a curve applied to the final grade.

Robert Tran 1B

I think since that was covered before the midterm, we will not need to know how to identify acids and bases for test #2.

Robert Tran 1B

The lone pairs in the sulfite ion cause the bond angles to be slightly smaller because the electron-electron repulsion pushes the bonds closer together.

Robert Tran 1B

A permanent dipole is caused by a difference in electronegativity. An induced dipole is caused by a charged atom or dipole that pulls electrons in one side, which causes a temporary dipole.

Robert Tran 1B

Hydrogen bonds can only form with N, O, and F because they are the only elements that have a high enough electronegativity to create a strong dipole moment.

Robert Tran 1B

No, we do not need to calculate the strength of bonds. However, we should be able to recognize trends in bond lengths.

Robert Tran 1B

I think all of them have to be memorized. He just demonstrated how to determine the shapes of a couple molecules in class just as an example.

Robert Tran 1B

The VSPER formula would be AX4, since there is one central atom and four bonded atoms. The E will not be included since there are no lone pair electrons.

Robert Tran 1B

Yes, on previous midterms there was an equation/constant sheet and periodic table attached to the back.

Robert Tran 1B

Expanded octets would be used if it's clear that there is more than 4 atoms bonded to the central atom (ex: XeF5). Also, the octet can be expanded if the formal charge favors it in the lewis structure.

Robert Tran 1B

There are some exceptions to the octet rule for these atoms. For example, CH3 is a radical, so it only has seven electrons around it, which breaks the octet rule.

Robert Tran 1B

I'm assuming if you're asked to find the smallest cation, it is given that all the cations have the same amount of valence electrons. In this case, the smallest cation would have the highest amount of protons because this would mean the nucleus has a stronger pull on the electrons.

Robert Tran 1B

You would need to calculate the formal charges of the atoms and add the single electron to the atom that would make all of the formal charges closest to zero.

Robert Tran 1B

An ionic compound has at least two atoms. Even in the atom that donated an electron, the nucleus still exerts a small attractive force on the electrons of the other atom(s). This causes them to be pulled slightly in one direction, which means they are slightly covalent.

Robert Tran 1B

Delocalization also occurs in other molecules, such as metals. However, as far as what we have learned in class, delocalization only applies to resonance structures.

Robert Tran 1B

Yes, because if there is a substantial difference in electronegativity, one element is more likely to give up electrons, while the other element is likely to take electrons.

Robert Tran 1B

Electron affinity is not as periodic as ionization energy. Thus, although electron affinity tends to increase going right and up, there are many exceptions to this.

Robert Tran 1B

To identify a radical, you usually have to look at the molecule's lewis structure and determine if there is an unpaired electron. If so, the molecule would be a radical.

Robert Tran 1B

If we are considering the anions and cations of one element, then the anion should be larger than the cation. This is because the anion will have more electrons, which creates more electron repulsion within the atom and increases the size of the electron cloud.

Robert Tran 1B

As "l" (the number corresponding to the orbital) increases, the orbitals become increasingly less likely to penetrate the nucleus. Since the electrons spend more time further from the nucleus as l increases, they also experience more repulsion from other electrons. This means that the ener...

Robert Tran 1B

ATingin_3I wrote:Also speaking of frequency, is frequency always measured in terms of Hz?

The SI unit for frequency is Hz (s^-1). However, 1 divided by any unit of time can be used to measure frequency (ex: 1/hr). These are often not seen though because it is impractical for chemistry.

Robert Tran 1B

There are only two possibilities for the spin direction of an atom: upwards and downwards. Because of this, there are also only two possible spin magnetic quantum numbers. I believe the numbers +1/2 and -1/2 were chosen somewhat arbitrarily.

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