CHEMISTRY COMMUNITY

Sanjana Borle 2K

When using the pre equilibrium approach, how do we know which step we need to use to find Kc or the equilibrium constant? Is it always the first step?

Sanjana Borle 2K

I dont conceptually understand the difference between k and k prime. Why does k eq equal k divided by k prime? Is it products over reactants?

Sanjana Borle 2K

Like the diagram in class, you can tell that there is a phase change when the heat or enthalpy is increasing, but the temperature is not increasing, or delta T is zero.

Sanjana Borle 2K

A galvanic cell is essentially where chemical energy drives electrical energy, so in this case E is positive and the reaction is favored. In a electrolytic cell, E is negative, which means the reaction is not favored and an electric current must be supplied in order for it to happen. In this case, e...

Sanjana Borle 2K

Since the composition of the cells is the same molecule, there would be no difference between E cathode and E anode, making the overall cell potential zero.

Sanjana Borle 2K

Using the equation deltaG=-nfE(naught), if E(naught) is calculated using E(cathode)-E(anode), and E anode is bigger, this means that the total cell potential will be negative. Since negative times negative is positive, delta G is positive, which tells us that the forward reaction is not favored, but...

Sanjana Borle 2K

Yes, n is the amount of electrons transferred. When you add the half reactions to get the total reactions these number of electrons should cancel out

Sanjana Borle 2K

Since you flip the equation for the anode when writing out the total equation for a cell, it makes sense that Q would be anode/cathode because this way the anode becomes the product.

Sanjana Borle 2K

Adding water will dilute a solution, and depending on whether it is added to the anode or cathode, delta G, or work, may also go up or down.

Sanjana Borle 2K

I think all we need to know is that EMF is the same thing as the cell potential, or the variable E, so if a problem refers to emf it is just referring to E.

Sanjana Borle 2K

I dont understand conceptually how the standard Gibbs free energy for pure substances is also zero, like delta H standard. Since the equation for Delta G is H-TdeltaS, why doesnt the TdeltaS part factor in? Why is it still zero?

Sanjana Borle 2K

Can someone explain the conceptual reasoning behind why a concentration cell is available to do work if the concentration of ion in the anode is lower than the concentration of ion in the cathode? Is it because then electron flow will go from anode to cathode to balance out charges?

Sanjana Borle 2K

Yes, usually in cell diagrams you write the anode then the cathode from left to right, so to keep it consistent it makes sense to do this.

Sanjana Borle 2K

Diamond is thermodynamically unstable because the delta G to go from Diamond to graphite is negative, which means the reaction for that to happen is favorable. However, it is kinetically stable, at least at standard temperature and pressure, because the rate of the reaction would be so slow that ess...

Sanjana Borle 2K

Yes, the E value corresponds to the element with the highest oxidation.

Sanjana Borle 2K

If there was no salt bridge, the reaction would stop due to overly high concentration of negative or positive ions in the anode/cathode. By balancing out these charges with the anion or cation, the salt bridge helps the reaction to proceed.

Sanjana Borle 2K

In a concentration cell, essentially the reduction half reaction and oxidation half reaction cancel each other out because the same type of solution is used in both compartments of the cell.

Sanjana Borle 2K

The test will only cover the part of thermodynamics that we learned after the midterm (ie the rest of the Gibbs free energy equations) and the electrochemistry applications outline. Anything after that will not be tested, even if it is lectured on.

Sanjana Borle 2K

Yeah, my TA also said that you can assume that the charge of Oxygen is -2. Using this known value we can use it to find the oxidation numbers of other elements.

Sanjana Borle 2K

As Dr. Lavelle explained in class today, the reaction is favorable if Ecell is positive, because that means that delta G is negative. When delta G or Gibb's free energy is negative, that means the reaction is favorable.

Sanjana Borle 2K

Since standard cell potential is calculated using standard conditions, the stoichiometric coefficients do not affect it.

Sanjana Borle 2K

For 5C on the pizza rolls, it is false that one cannot calculate the entropy of vaporization for water at room temp because water has a boiling point of 373K. How would you calculate entropy of vaporization without raising the temperature? I dont understand how it is false.

Sanjana Borle 2K

What about aqueous?

Sanjana Borle 2K

How does entropy of a substance in aqueous phase relate to entropy in the gas, liquid, solid, etc. phase?

Sanjana Borle 2K

How do we know that a system is not doing work on the surroundings? Would the only case for this be that the system is not expanding?

Sanjana Borle 2K

For the equation for isothermal reversible expansion, w=-nrTln(V2/V1), are the final temperature, moles, pressure used always?

Sanjana Borle 2K

Yes, in an adiabatic process q equals to zero because there is no transfer or heat between a system and its surroundings.

Sanjana Borle 2K

If we are given a problem that involves a substance that is not an ideal gas, Cp and/or Cv will probably be given in the problem right?

Sanjana Borle 2K

Bond enthalpies should be given. The only type of problem that we would need bond enthalpy for is for calculating delta H, and subtracting the bonds formed from the bonds broken. In this case its usually helpful to draw out the structure.

Sanjana Borle 2K

For enthalpy and heat, the only differences between them (q and H) is that enthalpy is a state property and the heat is not, correct? When are we supposed to assume that they equal each other?

Sanjana Borle 2K

I'm a little confused with the difference between an adiabatic and isothermal system. For isothermal since delta T is 0 and for for adiabatic system q is 0 does it mean that all isothermal systems are adiabatic and vice versa? since q=ncdeltaT?

Sanjana Borle 2K

Usually for thermodynamics problems Kelvin is used, but for many equations it doesn't really matter because the difference in one degree of Kelvin is the same as that of Celsius.

Sanjana Borle 2K

I don't think we need to memorize them.

Sanjana Borle 2K

It does not matter for the most part because the change in temperature in one degree of Celsius is the same as the change in temperature in one degree of Kelvin.

Sanjana Borle 2K

Phase Changes occur when temperature is constant, and the temperature goes up as the entropy of the solution goes up; however it doesn't undergo a phase change at this time.

Sanjana Borle 2K

Delta H is measured in heat, whereas Q means enthalpy. Enthalpy is a state property, whereas heat is not.

Sanjana Borle 2K

The equilibrium constant does not change with pressure.

Sanjana Borle 2K

Strong acids are usually ones that give off protons easily, such as HF or HCl. Strong bases will give off OH- easily, such as NaOH.

Sanjana Borle 2K

Bond enthalpies are only accurate with diatomic molecules with atoms of the same type, otherwise it is not so accurate since the enthalpy is calculated using averages.

Sanjana Borle 2K

I believe it was anytime this week after 11 but they should be handing them out next week too.

Sanjana Borle 2K

Yes, you can assume that the temperature is 25 degrees and you can use the equation.

Sanjana Borle 2K

Kp is the constant given by the partial pressures of the gases, and Kc is the equilibrium constant given by the concentrations of gases. They are both calculated the same way but will result in different numbers. I'm pretty sure that if we need to know them then the conversion constants will be give...

Sanjana Borle 2K

Is water included in the K constant expression if it is a gas? Is it only not included when it is a solvent?

Sanjana Borle 2K

If Q is less than K, then it means that there are more reactants than products when compared to equilibrium, so more products need to be formed.

Sanjana Borle 2K

Your best resources are probably the 2 Outlines as well as the Peer Learning and Step Up sessions.

Sanjana Borle 2K

If the initial concentration (such as 0.1-x) is small enough, then you can "take away" the x from the bottom ONLY since it is probably a small number, but this is just to make calculations easier. Technically it's not mathematically correct but the difference if you used the quadratic form...

Sanjana Borle 2K

Yes, generally an ice table is used if you know initial concentrations, and the K value. I dont think we have seen many other variations of this.

Sanjana Borle 2K

Also for solids and liquids, pressure does not affect them, in other words they can't be compressed further, whereas gases can.

Sanjana Borle 2K

If you compare Q to K, you can determine whether the reaction is going go to in the forward or reverse reaction to reach equilibrium.

Sanjana Borle 2K

Im not sure but I believe we might have to, since an equation sheet and periodic table is all we get.

Sanjana Borle 2K

As we learned in class, change in pressure generally does not change state of equlibrium.

Sanjana Borle 2K

Essentially, because the reaction wants to reach equilibrium again after you add more reactant, that reactant will go through the reaction to form the product and the reaction will move forward, causing more product to form till it reaches equilibrium again.

Sanjana Borle 2K

Kc and Kp eventually lead to the same conclusion, it's just that Kc uses concentration and Kp uses pressure.

Sanjana Borle 2K

Unless all four surrounding molecules are the same, all tetrahedral molecules are polar.

Sanjana Borle 2K

Can someone explain why boric acid is a Lewis acid and an electron pair acceptor? Also does this mean that the conjugate base of boric acid is not stable since boric acid is a weak acid?

Sanjana Borle 2K

Since the structure of this molecule is tetrahedral, it is not the same that it looks when drawn as a 2 d Lewis structure. Essentially a tetrahedral structure can be rotated in different ways that is not accurately depicted in a 2 d structure, so if the H's and Cl's were opposite each other the mole...

Sanjana Borle 2K

"Cyano" is the conventional way of naming whereas "cyanido" is the new IUPAC way of naming. I believe that Lavelle accepts both, but uses the conventional way in all his examples. They both mean the same thing and either one is acceptable.

Sanjana Borle 2K

cyano and cynanido essentially mean the same thing; I believe Lavelle accepts both on his tests, but uses the cyano. For more information refer to the Coordination Compounds pdf on his Chem 14A website.

Sanjana Borle 2K

Molecules with just London Dispersion forces do not have polarizability, as they are nonpolar. These forces are present in all molecules, even nonpolar ones.

Sanjana Borle 2K

If Cl were to be a central atom in a molecule and there four surrounding atoms, would it be wrong to have 3 double bonds and a single bond in the molecule? Since in that case the formal charge of Cl is zero and it can expand its octet, would this technically be correct or 14 electrons too much?

Sanjana Borle 2K

Basically electronegativity determines the electron withdrawing ability of atoms in a molecule, and therefore its acidity. So for the CH3 vs CCl3 example, since Cl is more electronegative, the Cl atoms pull the e- density closer to themselves, making the H easier to detach.

Sanjana Borle 2K

A ligand is a molecule that attaches to a metal cation to form a coordination compound. A ligand can be a mono or poly dentate, which means it "bites" to the metal in one place or in multiple places. This depends on the structure and flexibility of the ligand.

Sanjana Borle 2K

Nothing has been curved yet, but I believe that in the past Dr. Lavelle has curved the final grades of the class.

Sanjana Borle 2K

The general trend is that acids like to become more negative and bases like to become more positive. Therefore, an acid in the Lewis definition is an electron pair acceptor and in a Bronsted definition a proton donor, and a base in the Lewis definition is an e- pair donor and a proton acceptor in th...

Sanjana Borle 2K

I think the most we will have to know about cisplatin is how to draw it and why it is used as a chemotherapy drug whereas trans platin is not.

Sanjana Borle 2K

Also I believe that the singly bonded oxygens and the nitrogens have electron lone pairs that can form coordinate covalent bonds with said metal, so it chelates and binds to metals.

Sanjana Borle 2K

We do not need to know about bond order; it helps to refer to the outline to see what exactly in the book we covered.

Sanjana Borle 2K

Is there a periodic trend in terms of this? Does this mean that HF is the weakest acid, then HCl, then HBr, then HI?

Sanjana Borle 2K

Does Ka 3 mean Ka1 plus Ka2? Is is the overall Ka for the reaction?

Sanjana Borle 2K

I thought we use bis tris etc when naming multiple of the same polydentate? or is this the same thing?

Sanjana Borle 2K

Since Cl- has a octet, it will not have an affinity to other ions or water so it won't affect the pH

Sanjana Borle 2K

I think the one other exception we would need to know is for copper; it has a latin prefix of "cupr"

Sanjana Borle 2K

I think we also need to know how to name them, as discussed in class.

Sanjana Borle 2K

I think we do, because he talked about the different structures that coordination compounds can have, like tetrahedral, octahedral, square planar.

Sanjana Borle 2K

I believe we also need to know what a carboxyl group looks like, as well as other structurs we learned such as benzene or ethene.

Sanjana Borle 2K

Coordination number is simply the number of bonds formed.

Sanjana Borle 2K

Why is ciplatin square planar and not tetrahedral?

Sanjana Borle 2K

I believe the -ic vs -ous depends on the composition of the anion. For nitric acid it is produced when a H+ bonds to the nitrate anion, and for nitrous acid it is produced when an H+ bonds to a nitrite anion. In general, an "ate" anion corresponds to an "ic" acid, and an "it...

Sanjana Borle 2K

I'm not sure, but I'm guessing so; we have already been tested on everything else. This would be a good question for Dr. Lavelle or any of the TAs

Sanjana Borle 2K

In more detail, a conjugate base is produced when an acid donates a proton, and a conjugate acid is produced when a base accepts a proton.

Sanjana Borle 2K

i think the final will have two more questions than the midterm, i believe it is similarly structured.

Sanjana Borle 2K

Does this mean that we will be covering all new material up until Friday?

Sanjana Borle 2K

The best way is to know the chart and which shape corresponds with which AXE formula.

Sanjana Borle 2K

The brackets are what is inside the coordination sphere, which can be determined by the shape of the molecule.

Sanjana Borle 2K

If a atom has a very high electronegativity, it will pull on the electrons more and therefore form a stronger bond.

Sanjana Borle 2K

So the shape of an atom will help you determine whether the dipole moments cancel out, and therefore whether the molecule is polar or nonpolar. You need to know the 3D geometry because there are some molecules that can be drawn in a Lewis structure to look "symetrical" but are actually not...

Sanjana Borle 2K

You do not have to write a subscript if it is just 1, it's like math.

Sanjana Borle 2K

A lewis acid is an electron pair acceptor and a Lewis base lends an electron pair. The bronsted definition is that an acid is a proton donor and a base is a proton acceptor.

Sanjana Borle 2K

Since there is a lone pair that replaces the atom in a trigonal bipyramidal, it "pushes" on the other atoms and causes their bond angles to decrease.

Sanjana Borle 2K

I believe they will be covered after the midterm.

Sanjana Borle 2K

The second best option is to make sure that the more electronegative atom has a negative charge, and vice versa. this is considered the correct lewis structure.

Sanjana Borle 2K

Not only are some elements in the d block exceptions to the octet rule, so are the first four elements (hydrogen, Beryllium, Helium, and Lithium.

Sanjana Borle 2K

Adding on to that, since metalloids neither have "too many" or "too little" valence electrons as can be seen by where they are placed in the periodic table, they can go either way and lose electrons or gain electrons. Hence, they are called metalloids.

Sanjana Borle 2K

No, I believe not. Informal charges do not exist.

Sanjana Borle 2K

Due to the concept of resonance, technically double and triple bonds can be anywhere as long as the satisfy the octet rule. Just make sure to count up all the electrons before you place the double and triple bonds in a certain location

Sanjana Borle 2K

For me it really helps to count up all the total electrons in the structure and see if it matches my Lewis structure to check my work. It also helps for me to draw the atom in the center, which is the one with the least ionization energy, first so that I can draw everything around it after.

Sanjana Borle 2K

Same spin means that the electrons spin in the same direction (parallel to each other) and have the same quantum number (1/2 or -1/2). According to Hund's rule all electrons that are unpaired in an orbital will have the same, or parallel spin, but if there is more electrons and it requires pairing u...

Sanjana Borle 2K

It would probably be really helpful to go to the step up sessions, since those start from the beginning and once you feel more comfortable you can go to the drop in ones. I also wouldnt stress about memorizing formulas because many will be provided but its important to know units (eg use kg and not ...

Sanjana Borle 2K

I am not sure why the 1/2 is there for the spin quantum number but it may be because the other quantum numbers are integers

Sanjana Borle 2K

if n is 2, l is 1, and ml is -1 then the electron is in -2px state because the n number corresponds to number of orbital and l corresponds to the fact that its a p orbital, and as mentioned above the -1 corresponds to the x axis. It is true that the orientation is arbitrary but the ml number tells u...

Search found 111 matches