CHEMISTRY COMMUNITY

Rachael Cohen 3G

Those equations would still work. Personally, I find it most helpful to draw an energy diagram for these types of problems.

Rachael Cohen 3G

For this class I think we can assume it will not change and that any values we need will be given to us.

Rachael Cohen 3G

This is correct, although there may be different notation for the rate constant of the reverse reaction. Just take note of the notation, as the question should make it clear what k' means or what value is the value for the reverse reaction.

Rachael Cohen 3G

Galvanic cells operate on a reaction between two different species with two different reduction potentials. Concentration cells involve two electrodes of the same species, so their reduction potential is the same. They operate on a concentration gradient.

Rachael Cohen 3G

I don't think we need to worry about it, I think he just wanted us to know that there are other methods.

Rachael Cohen 3G

n is the number of moles of electrons being transferred in the reaction.

Rachael Cohen 3G

In this case you would use the 8.314 value. It helps to look at the units of the different R values and choose one that will cancel out the units of the other numbers you have, leaving you with the units you want for your answer.

Rachael Cohen 3G

They are both the same. I like to use the one that solves for k when I am looking for k but the one with ln(k) when I am looking for other variables.

Rachael Cohen 3G

Catalysts lower the activation energy of both the forward and reverse reaction, so equilibrium would not change.

Rachael Cohen 3G

You would need to convert them if the question asks for your answer in mol/L.

Rachael Cohen 3G

Like others have said, I believe we only have to know how pressure, volume, temperature, and adding or removing species in the reaction affect equilibrium. Pressure/Volume: Compressing a gas mixture will decrease its volume, increasing its pressure, and equilibrium will shift towards the side of the...

Rachael Cohen 3G

I don't think we've learned a way to determine what the slow step is just from the reaction mechanism, so I think it would be given to us.

Rachael Cohen 3G

If this is from Sapling question 7, then you have to use the data provided to find the orders. You can write out the rate law (leaving the exponents as variables) for two different experiments and divide them to solve for those variables.

Rachael Cohen 3G

I think for the sake of this class they will always tell us which step is the slow step.

Rachael Cohen 3G

Your steps look correct! Sometimes I get confused about balancing in basic conditions though, and in one of the UA sessions I was taught you could just balance it in acidic conditions first, and then however many H+ you have, you add that many OH- to each side. That way, the H+ and OH- combine to fo...

Rachael Cohen 3G

DeltaU is 0 in reversible reactions.

Rachael Cohen 3G

Enthalpy is a state function because it does not depend on the pathway of a reaction. Heat, on the other hand, is a property intrinsic to a certain species and its formation, so it is dependent on the pathway.

Rachael Cohen 3G

I agree with you that based on that article, the presence of a catalyst could change the order of a reactant. I think this makes sense since we know a catalyst changes the pathway of a reaction, so it could very easily change the order of the reactants. But of course I'm not a professional. This is ...

Rachael Cohen 3G

I don't think Gibbs Free Energy is connected very closely to the kinetics we learned in this course. It is connected to electrochemistry though.

Rachael Cohen 3G

Yep! So if you have something like ln(a)=b:
ln(a) = b
e^(ln(a)) = e^b
a=e^b

just remember to put e on both sides!

Rachael Cohen 3G

If the half-reaction does not have a conductive solid, then you will need to add Pt(s) or any other inert metal as the electrode. Remember, the solid must be a conductive metal, so if the solid is something like I2(s) (a nonmetal) you would still need Pt(s).

Rachael Cohen 3G

I think it's always best to do the calculations to determine the order. In this question, the reason all of the C concentrations are different and it is zero order is because two of the experiments had the same rate. Because a change in the concentration of C did not affect the rate, we know it is z...

Rachael Cohen 3G

Enzymes are an example of catalysts. They change the pathway of a reaction in order to lower the activation energy.

Rachael Cohen 3G

How I like to think about it is that the species that is being oxidized is losing electrons, and those electrons have to go somewhere. They go to another species, causing it to be reduced. So, the species being oxidized is causing the reduction, and is the reducing agent. The opposite is also true -...

Rachael Cohen 3G

The Van't Hoff Equation is used to find the equilibrium constant at a different temperature. So, if you are given the equilibrium constant at one temperature and asked for it at another, you would use this equation.

Rachael Cohen 3G

Determining the rate law can be done in a lot of different ways. The main one that comes to mind is when we are given a table of concentrations and rates and we are asked to calculate the orders of each reactant and to calculate k so we can write the rate law. Is this what you're asking about?

Rachael Cohen 3G

I think this is what question #3 from Saplings weeks 9/10 asked us to do, and we were given the linear tangent line so the rate (the slope) was pretty simple to calculate. Calculating the rate from a curved graph would require some calculus which I don't think is necessary for this course. Hope this...

Rachael Cohen 3G

I think that Thermodynamics refers more to the laws of thermodynamics that we learned regarding enthalpy and entropy. This involves the behavior of a system and its equilibrium. The constants we learn such as deltaH, deltaG, and deltaS are state functions, so the pathway taken to get from from the i...

Rachael Cohen 3G

I believe that they are closely related. I also think that for the scope of this class, we won't have to have a very deep understanding of this.

Rachael Cohen 3G

I don't think the order between each phase matters. I think the main thing is that the metal is on the outside.

Rachael Cohen 3G

Catalysts will appear in the reactants of a step and the products of a later step. Intermediates appear in the products of a step and the reactants of a later step. Hope this helps!

Rachael Cohen 3G

I think you got the cell potential for gold rather than silver.

Rachael Cohen 3G

In addition to H+ being +1 and oxygen generally being -2, it can also be helpful to know that the halogens are generally -1, the alkali metals are generally +1, and the alkaline earth metals are generally +2.

Rachael Cohen 3G

Start by writing out the two half-reactions involved. Then, balance the elements in each half-reaction. Add H2O to balance out oxygens and add H+ to balance out the hydrogen from the H2O. Add electrons to balance the total charges on each side of each half-reaction. Then add the two half-reactions t...

Rachael Cohen 3G

It helps me to write out as much as possible. For example, if I'm going to multiply an entire half-reaction by a coefficient of, lets say, 3, I will write it on two lines: 3(half -> reaction) 3half -> 3reaction This way I know that I multiplied it by a coefficient. It makes these problems take up a ...

Rachael Cohen 3G

I've had issues when I open the assignment from the Week 8 tab on CCLE. It seems to work if I open Sapling first and then select the assignment.

Rachael Cohen 3G

Sn and Mn are solids so they are not included in the equilibrium constant.

Rachael Cohen 3G

If you get tripped up about it being in a basic solution, balance the reaction entirely in acidic solution first. Then add the same number of OH- as there are H+ on both sides. The OH- and H+ will combine to form H2O. If there is now H2O on both sides, cancel out the excess. This might sound confusi...

Rachael Cohen 3G

I think that in practice, the order of the species in the shorthand shouldn't matter, because in context it is clear which species is going to be doing what in the cell. I'm not sure why Sapling wants it in a particular order.

Rachael Cohen 3G

The equation we're working with is:
2H+(aq) + 2e− -> H2(g)
Q is products over reactants. H2 is a gas, so we use the pressure. H+ is aqueous, so we use the concentration. Hope this helps!

Rachael Cohen 3G

States of matter should always be included, as different rules apply to different states of matter (what is included in an equilibrium constant, for example). I think that Sapling lets us omit them just to make it easier to submit our answers. For Sapling just make sure to always read the instructio...

Rachael Cohen 3G

I'm getting the same answer you did. Make sure you input the charges as exponents. I know a lot of people are having glitches with Sapling right now so maybe just try closing it, reopening it, and inputting it again.

Rachael Cohen 3G

I know this question is from a few weeks ago, but could you explain why you divide by the temperature change for part a?

Rachael Cohen 3G

Can someone explain what the n and m values in this formula would be for this problem? thanks!

Rachael Cohen 3G

MCl3(aq) is not in the final reaction, so we have to cancel it out. MCl3(s) is in the final reaction. This is one of the problems where the state of matter is really important to look at.

Rachael Cohen 3G

Percent ionization tells us how much of an acid or base ionizes in solution. Strong acids and bases ionize 100%, so for example all of the acid HA becomes H+ and A-, and the reaction only proceeds in one direction. When percent ionization is less than 100%, the acid or base is weak, creating an equi...

Rachael Cohen 3G

At pH values below the pKa, the protonated species of HA will become more predominant. HA is neutral. A- is the only charged species in the solution.

Rachael Cohen 3G

I'm pretty sure those are the only two transformations. Although we normally don't deal with fractions as coefficients, they still function the same way as whole numbers. Just remember that the transformations for K values are different. Instead of switching the sign, you do 1/K, and instead of mult...

Rachael Cohen 3G

I find that ICE charts are always useful for problems that give you any concentrations. They're a great way to organize the information you have. Sometimes you might not actually need one, but I think they help conceptualize the information you're given.

Rachael Cohen 3G

I would treat this kind of question the same as any other weak acid/base question. ClO- is a weak base, so the formula we're looking at is in the form B + H2O <-> BH+ + OH-. The base is ClO-, and BH+ is HClO+. Hope this helps!

Rachael Cohen 3G

You need to add the given equations together in a way that will create the formula it asks for. So, for example, to get 2MCL3(s) in the products, you will need to reverse the equation MCl3(s)⟶MCl3(aq) and multiply it by 2 (so you will change the sign on its delta H and multiply it by 2). Then, to ca...

Rachael Cohen 3G

When he introduced Q in the lecture, and the comparisons you can make between Q and K, Dr. Lavelle gave an example of performing an experiment on a lake, where you do a reaction in the lake and measure the concentrations. He said you might find, based on Q and K, that what you thought was the reacta...

Rachael Cohen 3G

So I understand that to really make a statement about equilibrium based on the K value, it needs to be less than 10^-3 or over 10^3. Does anyone know why in previous courses I have always been told to just use K<1 and K>1?

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