CHEMISTRY COMMUNITY

Hope Hyland 2D

Yes, I think you can ignore it since temperature isn't part of the equation for reaction rate.

Hope Hyland 2D

6.43
a) applies to Ecell only
b) both are temperature dependent (look at the equations for both)
c) neither --> both are dependent on n, so they won't change if you multiply by a constant
d) Ecell naught only because Ecell=0 at equilibrium
e) Ecell only

Hope Hyland 2D

n is the number of electrons being transferred (after balancing the half-reactions)

Hope Hyland 2D

Is this the same as the graphs we use to determine reaction rates?

Hope Hyland 2D

I'm pretty sure all the review sessions were cancelled and there's no online ones in place... but I know some students were planning on doing their own review session going through the endgame problems

Hope Hyland 2D

A reducing agent just means the species that is oxidized, AKA the species that's giving up electrons (since those electrons REDUCE the other species, this is called the reducing agent). An oxidizing agent is the opposite--it's the species that is reduced, since it's gaining electrons, it must take t...

Hope Hyland 2D

What does electrolytic mean?

Hope Hyland 2D

Also, how do you know if a metal/other compound is a strong reducing/oxidizing agent?

Hope Hyland 2D

How does changing the concentration in a concentration cell affect the cell potential?

Hope Hyland 2D

How do you know what n is when the half reactions have different numbers of electrons being transferred? Would you balance them and use that number?

Hope Hyland 2D

ursulavictorino1K wrote:Is a base a proton acceptor or donor?

A base is a proton acceptor!

Hope Hyland 2D

I think you just have to know which molecules actually form ionic bonds, and assume all the others are just conceptual.

Hope Hyland 2D

I also think this is correct! It makes sense if you kind of match up each phase with the galvanic cell diagrams we drew in class.

Hope Hyland 2D

I think you can do it either way, it's just easier to have the specific product/reactant that you're focused on, without a fraction in front.

Hope Hyland 2D

Also, what is the significance of electromotive force? I don't remember what Dr. Lavelle said about it in lecture.

Hope Hyland 2D

I'm not sure what you mean, could you give an example of what you're referring to?

Hope Hyland 2D

Yes, like everyone has said, I think cell diagrams are just a way for you to visualize what's happening during a redox reaction, as well as see what materials are used and which reactants are being reduced/oxidized, etc.

Hope Hyland 2D

Also how do you know where everything goes in a cell diagram?

Hope Hyland 2D

How do you use the oxidation numbers/states to get the half reactions? Also do we need to memorize the oxidation numbers for common molecules/elements?

Hope Hyland 2D

To balance redox reactions, you want to balance the electrons transferred in the reduction reaction and the oxidation reaction. To do so, you want to separate the whole reaction into two half reactions: the reduction reaction (gaining electrons) and the oxidation reaction (losing reaction) by writi...

Hope Hyland 2D

What equations/assumptions do you use when it tells you there is constant pressure? What about constant volume?

Hope Hyland 2D

Hello, this may be a dumb question but I don't get how to convert liters to cubic meters. I know on the formula sheet it says 1 L=1 dm^3 but I have absolutely no clue what a dm is. Thanks!

Hope Hyland 2D

Whenever I encounter a salt solution/buffer problem, I immediately get confused. Can someone explain what exactly a salt solution is, and how to go about finding the pH? I don't really understand the context of these questions so I think that's why I'm confused. It would be awesome if someone could ...

Hope Hyland 2D

I know delta G is for sure 0 at equilibrium, since there's no change in the free energy, but I'm not sure about delta H or delta S. I don't think they would be at zero, since the reaction is still occurring (because equilibrium is dynamic).

Hope Hyland 2D

I had the exact same question! The first time I did it, I got +312kJ by subtracting the enthalpies of formation of reactants (C2H2 and H2) from the enthalpy of formation of product (C2H6). But in the solution, it looks like they just added all the enthalpies of formation, but flipped the sign of the...

Hope Hyland 2D

How do we know when to use Cv, and when to use Cp?

Hope Hyland 2D

I'm not sure you'd be able to directly find pOH if you were only given pKb. Pretty sure you would also need the initial concentration of reactant/product or some other values to plug into your ICE table, for which you would use pKb to find the pOH.

Hope Hyland 2D

Since Q denotes the amount of heat transferred to a system, a negative q value would mean that the system is releasing heat, and a positive q would mean that heat is going into the system. But usually we use enthalpy (∆H) to determine whether a reaction is endothermic or exothermic. Enthalpy is simp...

Hope Hyland 2D

I think it's because if a process is isothermal, it means the temperature isn't changing, so there's essentially no transfer of heat, so q=0. Then, since q=w, as you stated, w also equals 0. Internal energy = q+w, so 0+0=0.

Hope Hyland 2D

I saw that too. I don't think we have gone over those things in class, and I'm not sure we will. But maybe we'll come back to it? Not sure, I'd skip that reading for now but it probably wouldn't hurt to read it.

Hope Hyland 2D

I don't believe he's covered this yet, but we do have the general equation $\Delta U$ =q+w.

Hope Hyland 2D

In a closed system, heat can still be transferred, but in an isolated system, neither heat nor matter can be transferred.

Hope Hyland 2D

Yes, the equilibrium shift only occurs if the pressure changes due to changes in volume. For example, if a gas is compressed, or the volume is decreased, then the pressure increases and equilibrium shifts to the direction with less moles.

Hope Hyland 2D

This one tricked me too! You have to use the ideal gas law, so PV=nRT and just plug everything in. But make sure to convert everything to the right units.

Hope Hyland 2D

This problem says: The percentage deprotonation of benzoic acid in a 0.110M solution is 2.4%. What is the pH of the solution and the Ka of benzoic acid? I understand how to use the percentage deprotonation to find the pH, but I am confused on how to find Ka. In the solutions manual, I have the same ...

Hope Hyland 2D

I was also really confused on how to get the answer to parts (i) and (ii) of this question. How come you can't use the given value of [H30+]=1.5 mol.L-1 and then substitute into [H30+][OH-]=10^-14 to find [OH-]? I tried doing that, but I kept getting the wrong answer.

Hope Hyland 2D

Why is it that when a system's pressure is increased by decreasing the volume, the reaction will shift toward the side with less moles, but when a system's pressure is increased by adding an inert gas, nothing happens?

Hope Hyland 2D

if delta h is positive for a reaction (aka endothermic, or requires heat), and you increase the temperature, then the reaction will favor the formation of products since the heat is used to make products. As a result, K will increase for endothermic reactions when the temperature is increased. On th...

Hope Hyland 2D

I think you use it anytime you make an approximation, or assume that x is so small that it's essentially equal to 0.

Hope Hyland 2D

I don't believe that buffers will be on the test, but you should definitely know how to find the pH of weak acids/bases.

Hope Hyland 2D

I'm pretty sure you would use the same process as if there were reactants used in the equation. Still make an ICE table, putting in the information that is known (initial concentration of NH3 is given), and then assume that both products increase by x, so you would have [NH3]=0.200+x and [H2S]=x as ...

Hope Hyland 2D

Yes, so you would do the same process as usual to find the equilibrium concentration for HClO2. You can create an ICE table, fill in the known values, which in this case, you know the initial concentration of HClO2. Then, you can call the change in concentration for each molecule in the reaction &qu...

Hope Hyland 2D

The Cl is not included in the equation because it's not involved in the reaction, so it would just cancel out anyway.

Hope Hyland 2D

The conjugate base for HCOOH would be HCOO-, and since the pKa is 3.75, you can subtract that from 14 (pKa+pKb=pKw=14), and get 10.25 for the pKb.

Hope Hyland 2D

You can only calculate K for equations that are at equilibrium, which is usually indicated in the problem. If the equation is not balanced, then balance it and then find K (assuming the reaction is at equilibrium). Conversely, Q is calculated when the reaction is NOT at equilibrium, and is simply th...

Hope Hyland 2D

Solids and liquids typically don't change concentrations at all during reactions, so they are not included in the equilibrium constant.

Hope Hyland 2D

Q is the reaction quotient, whereas K is the equilibrium constant. While they are both ratios of product to reactant, K represents the ratio when the reaction is at equilibrium, or when the forward rate of the reaction is equal to the reverse rate (products are being formed at the same rate as react...

Hope Hyland 2D

I think if the problem is dealing with gases, or it gives partial pressures, then you should use K_p, and if it's talking about concentrations then use K_c.

Hope Hyland 2D

Technically, the equilibrium constant (K) does not have units because it uses the activities of the reactants/products as its terms, rather than concentrations or partial pressures.

Hope Hyland 2D

Make sure you're reading the question very closely. Part D is comparing the initial concentrations of reactant (what you start with) and equilibrium concentrations of product (what you end up with once the reaction reaches equilibrium). It says that if you START with higher concentrations of reactan...

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