CHEMISTRY COMMUNITY

Megan Kirschner

Does this still apply to winter 20!? Re: We won't be required to draw graphs but be able to interpret them.

Megan Kirschner

Always go based on the order of the reaction:

If the reaction is zero-order, K has units of M/s
If the reaction is first-order, K has units of 1/s
If the reaction is second-order, K has units of 1/M.s

Megan Kirschner

I am confused about the same thing- could someone help us out???

Megan Kirschner

The intermediate can't exist in the rate law because something was used to form it.

Megan Kirschner

I think it's always good to find a friend who can attend different review sessions than you and then compare notes.

Megan Kirschner

An exothermic reaction- the activation energy is lower in the forward direction so if you heat up an exothermic reaction k reverse will increase which will result in a lower K and the reaction will favor reactants

Megan Kirschner

Thanks for the helpful answer. But I'm still unclear why it's important to know these things and what they can help us learn about chemistry?

Megan Kirschner

Who is Lyndon? Is he still a TA?

Megan Kirschner

For the solid on the far right or far left, do they have to be the same?

Megan Kirschner

I also don't understand that- could someone explain?

Megan Kirschner

I think it's likely it will focus on the thermodynamics stuff that wasn't on the midterm, beginning with the content taught during week 6. But obviously there can be overlap since it's all connected.

Megan Kirschner

Gibbs energy is like a chemical potential that is reduced to its minimum when a system reaches eq. at constant pressure and temperature. Gibbs and K are related because they can tell us what is likely happen in a reaction.

Megan Kirschner

The cathode is the one being reduced and the anode is the one being oxidized. The little pneumonic device I learned in high school to remember this was AN OX, RED COW. There's an ox (for anode and oxidation going together), and there's a red cow (for the pairing of reduction and cow for the c in cat...

Megan Kirschner

Rusting itself is a redox reaction so I imagine LuValle could ask us a question revolving around an example of rusting.

Megan Kirschner

It's always good to start by determining how many electrons to add to each part of the reaction by calculating the overall charge of each side of the reaction.

Megan Kirschner

Thanks for all the helpful tips!

I also was wondering if everyone knew if we will ever be expected to know specific heat capacity values by heart? Or will we always be supplied with whatever we need?

Megan Kirschner

Speaking of- does anyone know where problems from homework #6 are supposed to come from? I think thermodynamics, but we didn't cover all of it yet- so I'm not sure how to go about it.

Megan Kirschner

Yes, it's the same.

I often find it helpful to cross out the equations we don't know anything about- so the equations sheet is less overwhelming.

Megan Kirschner

I think basically the general ideas of Gibbes free energy and the central equation is what's expected (only the stuff from the first page of the outline on thermodynamics)

Megan Kirschner

They relate because they can tell you lots of things about if a reaction will occur spontaneously and if it's favorable. It is expected that how this could be presented on a test would be if you were given all or some of these terms and asked to deduce overall conclusions about the system.

Megan Kirschner

I think also phase change helps orient what values will be positive and negative. You need to take phase changes into account when calculating the change of enthalpy in a reaction (the calculations we use assume that all the reactants and products are gases).

Megan Kirschner

Delta U and delta H are interlocked cause the change in internal energy equals the change in enthalpy plus the work done on the system (this is one of the important equations in this unit).

Megan Kirschner

Everything for topics 1-4. I believe he said that he will begin and finish covering Gibbs free energy in the lecture this coming Wednesday and Friday. Does anyone know if we will be learning new things next week on Monday and Wednesday?

Megan Kirschner

Exactly- it helps you determine which variables are constant in an equation (and can thus be substituted for 0s).

Megan Kirschner

A positive delta H means energy is put in, which makes it endothermic, which is what is necessary to break the bonds that holds a solid together into a liquid. That's why the change in enthalpy is positive!

Megan Kirschner

Yea so essentially: standard enthalpies are the change of enthalpy during the formation of 1 M of the substance from its elements needed to make it, but bond enthalpies are the amount of energy required to break bonds. How I remember it is bond is B for break, and standard is s for synthesize.

Megan Kirschner

Yes- they will be specific values. Also, I believe it's safe to assume that we will either be given the specific heat or be asked to calculate it (when we have everything else given).

Megan Kirschner

I find that lewis structure is really about practice. I usually like to watch youtube videos and follow along and practice!

Megan Kirschner

So essentially: endo is adding energy/heat, and exo is when heat/energy is released

Megan Kirschner

Would anyone be able to describe the diagram you all are referencing? I was sick and unfortunately missed that lecture :/

Megan Kirschner

Since it depends on class average at the end of the quarter- does that sort of mean you can't calculate your grade at all throughout the quarter?

Megan Kirschner

Is the only requirement for the calculator that it cannot be graphing?

Megan Kirschner

Just checking- the five posts are due basically before your scheduled discussion section for the week?

Megan Kirschner

I would think if you had to miss a discussion one week you could email your TA and ask to give into your HW during a lecture during that week. Just an idea.

Megan Kirschner

I also don't understand why that one is 2 sig figs. Is there a place I could get good review on sig figs?

Megan Kirschner

So essentially H+ and H3O+ are the same things just expressed differently?

Megan Kirschner

The way I like to think of it is it can lie outside of the 0 to 14 range, but pH + pOH must equal 14 when added together.

Megan Kirschner

I understand the posts before this but what exactly is the definition of partial pressure? Just the fraction that a certain gas takes up? I am making it more complicated than it is?

Megan Kirschner

I've found that first simplifying the denominator is the key to making these problems go smoothly. Always start with that.

Megan Kirschner

I know it's early on in the quarter, but I can already tell that Dr. Lavelle is going to make a significant impact on my time at UCLA, specifically this quarter. He just makes the material so digestible and I truly appreciate his approach. He also seems to WANT us to succeed. Thank you already!

Megan Kirschner

I think it's super helpful to get to the exam site early to habituate yourself to the room. It can be off-putting to be in a new room without being familiar with it. I usually go an hour early to sit just scrolling through my phone or meditating. It makes when the test gets put out less scary.

Megan Kirschner

I understand that we use the ideal gas law for calculations, but how many gases actually behave in an ideal manner? How realistic are the calculations we get and is it mostly just theoretical or based on empirical data?

Megan Kirschner

What exactly defines an Inert gas? I understand the posts above except for this.

Megan Kirschner

K is y a ratio (between products and reactants) and so it does not have units- but so does this mean that all ratios we use in this class will be unitless? Is it safe to apply this rule widely?

Megan Kirschner

What exactly is the difference between Kc and Kp? I know (or think) they are equilibria constants but what do they individually represent?

Megan Kirschner

I understand the fact that you omit solids and liquids when calculating the equilibrium constant, but why? What's the logic behind it?

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