CHEMISTRY COMMUNITY

Sophie Roberts 1E

Can someone give in an example of an equation in which you would include the Hydrogen ion in the cell diagram? How would you include it, because you most likely will not use a porous disk to separate the ions since H+ will be in the same phase as one of the ions. But how do you know when to include ...

Sophie Roberts 1E

No, molecularity only depends on the molecules which react so we are only looking at the reactants. When considering molecularity we are evaluating how many molecules are colliding which again would only be considering the reactants.

Sophie Roberts 1E

It is important to differentiate between a catalyst and an intermediate. A catalyst is present from the beginning of the reaction and is not consumed. However, an intermediate is produced by the reaction and is used up in the reaction.

Sophie Roberts 1E

I dont recall prof Lavelle explaining in class but I remember him saying in this class we will generally be using A=1.

Sophie Roberts 1E

If the graph of [A] vs time is linear, then the reaction is zero order because the reaction rate is independent from the concentration of reactants.

Sophie Roberts 1E

You look at when the concentration of one reactant changes and the amount their corresponding reaction rates change. You then raise the concentration to the power "n" and set it equal to the change in reaction rates to find the exponents of the reactants in the rate law. Once you find the ...

Sophie Roberts 1E

If the graph of [A] vs time is linear then it's a Zero Order reaction.
If the graph of ln[A] vs time is linear then it's a First Order reaction.
If the graph of 1/[A] vs time is linear then it's a Second Order reaction.

Sophie Roberts 1E

When balancing half reactions, should we be just writing down the element that is involved or should we be including the entire compound that that element is apart of? Does it depend on the reaction and if the compound includes oxygen/hydrogen?

Sophie Roberts 1E

As said above, this is because the standard cell potential is an intensive property so it is not affected by a change in coefficients. However, if it was an extensive property, like Enthalpy, you would multiply its value by a change in the coefficients.

Sophie Roberts 1E

I’m confused on how to balance a redox reaction when there is one reactant that acts as both the reducing and oxidizing agent. For example, in #6K3 in the 7th edition textbook, it gives the equation: Cl2(g) —> HClO(aq) + Cl2(g) Cl2 is the only reactant and acts as both the reducing and oxidizing age...

Sophie Roberts 1E

One way to remember which (anode or cathode) is redox or oxidation is by using:
A RED CAT (redox--cathode)
AN OX (anode--oxidation)

Sophie Roberts 1E

It is most important to know they allow ion transfer which helps maintain neutral solutions.

Sophie Roberts 1E

Also it is important to remember when Delta G is negative the reaction is spontaneous!
When it is positive it is non spontaneous.

Sophie Roberts 1E

Gases have greater entropy, because gas molecules expand to fill their whole container and can move around freely so there is more disorder... So since this reaction goes from having one mole of gas to having zero, its entropy decreases.

Sophie Roberts 1E

hi miriam! They both represent different things.. the lowercase w is to calculate work done on the system which is used for reversible and irreversible reactions. While, the capital W represents degeneracy, so it used to calculate residual entropy.

Sophie Roberts 1E

In addition to what was said above, entropy can determine if a reaction is spontaneous (favorable) or not but Enthalpy cannot determine this.

Total entropy >>0 - Spontaneous
Total entropy <<0 - Non spontaneous

Sophie Roberts 1E

I saw a problem like this too, and was wondering if we can just use the enthalpies of formations for each of the compounds and use the equation:
Enthalpy of formation (products) - Enthalpy of formation (reactants)
Instead of doing Hess’s Law? Or will you get different answers?

Sophie Roberts 1E

Does someone mind listing all the important equations we need to know for the thermochemistry unit? I get confused when reading the book, which equations are necessary to know and which are just examples...
Thank you!!

Sophie Roberts 1E

How do you know when to you use Hess's Law to calculate the overall reaction Enthalpy versus when to use the equation: Enthalpy of formation for products - the enthalpy of formation for the reactants For example #4D15 in the 7th edition, I used the equation above but the solutions manual used Hess's...

Sophie Roberts 1E

I remember Lavelle going over this but couldn't remember his explanation... why must the constant pressure have a negative sign in front for the calculation of work done on a system?

Sophie Roberts 1E

Why is the greatest work done for processes that take place reversibly when the definition of a reversible process is one that can be reversed by a very small change?

Sophie Roberts 1E

Can someone please give examples for open, closed, and isolated systems? I'm still kind of confused by the definitions of them all so I think examples would help me understand the concepts better. Thanks!

Sophie Roberts 1E

Consider pressure in terms of volume as well. When the number of moles stays the same and the volume decreases, the pressure will increase because now there is a more concentrated system. Same vice versa, when the volume increases, the solution is less concentrated so the pressure decreases.

Sophie Roberts 1E

We use Q to determine which way the reaction must proceed to reach equilibrium which can also help us in settling up our ICE boxes.

Sophie Roberts 1E

Yes it is equivalent... it is just suggested to use mol/L when doing calculations so you are more aware of what units are being used and canceled and which remain.

Sophie Roberts 1E

Is the only thing that remains the same at equilibrium between two different size samples of the same reactants and products, the equilibrium expression (kc)? How come the ratio without the exponents changes but the ratio with the exponents doesn't change?

Sophie Roberts 1E

I'm confused on how to explain your observation for the change in volume in relation to the Le Chatelier principle. Lavelle said not to discuss the increase or decrease in moles when the volume is changed, but rather to discuss the reaction quotient. How would you do this? Can someone provide an exa...

Sophie Roberts 1E

The reaction quotient can be calculated the same way as K. The concentration values used for the calculation of Q are the values before the reaction reaches equilibrium, and the values used to calculate K are the values when the reaction is at equilibrium.

Sophie Roberts 1E

We assume the concentrations are very low and close to zero, so to make the calculations easier we just use 0.

Sophie Roberts 1E

A spectator ion is unchanged on both sides of the reaction and does not affect equilibrium so it is therefore not included in the equilibrium expression.

Sophie Roberts 1E

In the expression, you must put the concentrations of the reactants and products to the power of their stoichiometric coefficients!

Sophie Roberts 1E

It may also be helpful to memorize the main strong bases... group 1 and 2 hydroxides! It will be easier/faster to identify the strong base if you know the general strong bases.

Sophie Roberts 1E

You will know if water acts as an base or an acid based off of what compound it is reacting with. If it is reacting with a base, it will act as an acid and donate protons; however, if it is reacting with an acid, it will act as a base and accept protons. And I believe the strength of an acid/base do...

Sophie Roberts 1E

Amphoteric refers to a compound that can act as either a base or an acid. The most well known example of an amphoteric compound is water, because it can act as both a base and acid.

Sophie Roberts 1E

Polarizability is related to anions and how readily able they are to have their electron cloud distorted by the cation. Polarizability increases as atomic radius increases because more electron shielding. Polarizing power is related to cations and their ability to distort the electron cloud of anion...

Sophie Roberts 1E

This is referring to polarizability. The London Dispersion Forces are stronger when the anion is more polarizable and the anion has higher polarizing power. And the anion is more polarizable when it is larger because there is more electron shielding.

Sophie Roberts 1E

No I don't think we have to know the formula since we never really did any math with it, I think you just have to know the general concept of how potential energy relates to the behavior of IM forces.

Sophie Roberts 1E

Yes, Lavelle says he prefers to put the d-orbital after the s-orbital but either is correct notation!

Sophie Roberts 1E

In class today, Professor Lavelle said the number of hybrid orbitals = the number of electron density regions around the central atom.

Sophie Roberts 1E

I am also still confused on if all lewis structures obtain hybridized orbitals? Or how do you determine if they do or don't?

Sophie Roberts 1E

I'm not sure if we have to know this, but I remember in high school chem, we had to derive AX2 or AX2E2 or whatever based off of the number of bonding pairs and lone pairs on the central atom and from that, you could derive the shape of the molecule. I remember knowing this helped me a lot but I can...

Sophie Roberts 1E

I'm assuming we have to memorize the angles too because we are supposed to understand the concept of how lone pairs affect the bond angles, so therefore you should be able to derive the angles based on the shape of the molecule.

Sophie Roberts 1E

I think we have to know the bond angles of each shape and basically how those angles are derived. For instance, you have to know that by adding lone pairs, the angles will be affected and will generally become smaller.

Sophie Roberts 1E

Oxygen is the center atom because you also have to consider the bond formation. Oxygen forms more bonds than Chlorine, so it should be the center atom, since there are two other atoms to form bonds with.

Sophie Roberts 1E

Electron affinity is the energy given off when electrons are added to the atom. So basically, the electron affinity of an atom can determine if the atom wants electrons or not. On the other hand, ionization energy is the energy needed to remove an electron from an atom. They both increase across the...

Sophie Roberts 1E

All of these trends feed off of each other so it is important to understand all of them. For instance, ionization energy feeds off of atomic radius, as the smaller the radius, the higher the ionization energy, because the pull from the nucleus is greater. Another significant reason to know these tre...

Sophie Roberts 1E

I believe molecules are always the most stable when the formal charge is equal to zero because that shows that the molecule is neutral.

Sophie Roberts 1E

Resonance basically means that the lewis structure of a molecule can be written in different forms, but the one that is the most appropriate to use would be the one that has a formal charge of 0, because it means it is most stable. The general lewis structure of molecules with resonance would be the...

Sophie Roberts 1E

If it is not included in one of the sections listed in his outline or if he didn't go over it in lecture (which I think he only briefly addressed it), I don't think we will have to know it for the midterm! I don't think this topic will be focused on in the midterm, I would focus on the other ones li...

Sophie Roberts 1E

Since this number is determined off of the electron configuration, how do you know when to draw an arrow faced down or faced up so you can determine if it is +1/2 or -1/2?

Sophie Roberts 1E

4s would logically come next because it is the shell that is after Argon, however, in this case as we move onto the 3d level, we have to remember that the 3d level is less in energy than the 4s level. Electron configurations are always written in lowest energy to highest energy, so this electron con...

Sophie Roberts 1E

In addition to the all the previous replies, spin up and spin down is referenced when an atom has unpaired electrons (it subshells aren't filled).

Sophie Roberts 1E

I am also confused on this... For when you are asked to write the electron configuration, when do you not fill up the first orbital and move onto the next one? Like if you were to write 1s2,2s2,2p6,3s1,3p3,3d... How do you determine which orbitals you don't fill?

Sophie Roberts 1E

I am still confused on the variables l and ml that mean the orbital angular momentum quantum number and the magnetic quantum number. How do you determine both of these values when they give you a specific orbital?

Sophie Roberts 1E

I agree that sharing this info will be very beneficial for all of us! Personally, what I find to be quite helpful is handwriting my notes in class, so I can include equations and diagrams, but when I get back from class I type up my notes that I had just wrote down in class. I do this so that I am r...

Sophie Roberts 1E

Ground state means that the atom is not ready to bond with another atom, as it would be if it were in the excited state. Therefore, for the electron configuration for atom in the ground state, if possible, all of the electrons would be paired. On the other hand, for the excited state, there would be...

Sophie Roberts 1E

I was curious about this too, because I noticed in lecture today, Lavelle was asking the class what region a certain wavelength range was, so I am wondering if we have to know the general wavelength of each region or if we just have to know the relative strength.

Sophie Roberts 1E

As Melody said, I believe the book used the more exact number to match the number of sig figs in the data provided, and also it is helpful to use the more exact number instead of rounding to get a more precise calculation. However, since Lavelle noted 6.626 and most resources note Planck's constant ...

Sophie Roberts 1E

I am still confused what formula units are... In fundamentals E. 25 it says determine the number of KNO3 formula units in 0.750 mol KNO3.. Is that the same as saying the number of molecules/atoms? Where I am guessing you would use the conversion of moles to avogadros number.

Sophie Roberts 1E

For week 2 homework that is due during our discussion session, should we be doing 7 problems that are still from the high school review section or should we be moving onto the next topics? I was wondering because some discussions are after only one of the lectures so we haven't reviewed much of the ...

Sophie Roberts 1E

Do office hours begin this week? Also, when do the peer learning sessions start and what do those entail?

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