CHEMISTRY COMMUNITY

MadisonB

Isothermal expansion is where temperature stays the same and air is expanded, since heat is lost during work, heat is added.

MadisonB

Change in internal energy: ΔU
Internal energy: U

MadisonB

A good way to tell is to look at the other units you use in the equation. For example, the gas constant includes the unit, K, so you would need to use temperature in Kelvin's for the problem.

MadisonB

They are the least accurate because they are an average of all the possible molecular structures they can be in. If you actually compare the methods they are actually pretty similar, but the other two covered methods deal with more exact numbers based on the specific structures in the equations.

MadisonB

I would assume that you do not need to memorize any both enthalpies. In 14A, we were not expected to do any hard memorization. I would focus on problem solving skills and more conceptual things. Those are both things that Dr.Lavelle has generally shifted his focus to on past exams.

MadisonB

At equilibrium processes do not suddenly stop happening. So, equilibrium is defined as when the rate of transfer between the surrounds and the system are equal. An example could be a steaming cup of water. If you leave in a room at room temperature eventually the water will go to room temperate when...

MadisonB

I would assume not just because it wasn’t really covered in lecture or discussion sections.

MadisonB

You only look at gases, ignoring solids and liquids.

MadisonB

They usually provide all the equations you need to know. I find it best to look at it before the test so you are familiar where everything is.

MadisonB

If you think of the negative log of 1x10^-14, which is 14. The pH of the acid and the base always add up to 14, in a neutral solution both will be 7. (the below table is found at http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch17/ph.php) Pairs of Equilibrium Concentrations of H3O+ and OH- Ion...

MadisonB

Moreover, you use two arrows for weak acids and bases because there will be some sort of equilibrium where not everything is disassociated.

MadisonB

When inert gas is added to a system in equilibrium when pressure is kept constant, the volume will increases and moles on either side will shift. Conversely, if an inert gas is added to a system in equilibrium where volume is kept constant, the pressure will increase but the concentrations will not ...

MadisonB

Simply put, Q is at any moment and K is when in equilibrium. Q can be used to show change.

MadisonB

To post a question you will go to the board index and post under the topic that most closely relates to your question. It will probably be removed or changed if it's posted in the wrong category. After that, you click on the new topic button and ask your question.

MadisonB

Solids and liquids are regarded with a value 1 because their effective concentrations stay the same throughout the reaction.

MadisonB

Which are stronger oxoacids or binary acids?
For example: ClOH vs. HCl.

MadisonB

I do not think that we are expected to know this for 14 A.

MadisonB

These are some common strong acids: HCl - hydrochloric acid HNO3 - nitric acid H2SO4 - sulfuric acid (HSO4- is a weak acid) HBr - hydrobromic acid HI - hydroiodic acid HClO4 - perchloric acid HClO3 - chloric acid @https://www.thoughtco.com/list-of-strong-and-weak-acids-603642 You can also differenti...

MadisonB

As a side note, a tetrahedral complex is normally formed from AX4, while square planar is usually formed from AX4E2.

MadisonB

If you attended any of the review sessions for the midterm, we were given practice problems (as well as the "garlic bread" packet). Also, you might have gotten back previous tests.

MadisonB

You could also look at the problems on past tests or previous review sessions.

MadisonB

Yes, monodentates only have one donor atom. Going on, bidentates have two donor atoms.

MadisonB

A polydentate has more than two lewis base sites.

MadisonB

Some other indicators are pH values (above 7 is alkaline [base] and less than 7 is acid), and that H+ is usually found in relation to acids, while OH- is usually found in relation to bases.

MadisonB

It is the ratio of the s orbital to other orbitals. It is usually described by a percentage of s character. For example, sp3 hybrid has 25% s character.

MadisonB

If we didn't do it in class and it was never talked abut in sections, we probably don't have to do it on the test.

MadisonB

It depends on whether or not an element can have an expanded octet. Some elements can only have eight electron so formal charge does not matter because you can't add electrons (however, you might be able to go to a double or triple bond), while others can improve their formal charge (closer to zero)...

MadisonB

This is because it is a three dimensional shape so its wont just be 360 divided by the number of sides. This is a link to a mathematical proof laying out how to come to 109.5 degrees. http://www.ctralie.com/Teaching/Tetrahedron/

MadisonB

I do not believe so. Lavelle said that he only did them on the topics that he finds students struggle with the most. The most fundamental things.

MadisonB

The experimentally determined bond lengths of all the bonds are the same. Bonds lengths are the average of all of the resonance structures. I also got 130.

MadisonB

The syllabus says "Test 3 Starting Tuesday November 27 in discussion section."
Thanksgiving break is the week prior.

MadisonB

Polar: there is an uneven distribution of charge

Nonpolar: there is a completely symmetric distribution of charge

Video explaining this: https://www.youtube.com/watch?v=SiZXRScxbl0

MadisonB

https://i.stack.imgur.com/Z2n1k.png If you look at the above image you can see that when nitrogen has a positive charge (one less electron), it can form four covalent bonds. Either with single, double, or triple bonds. It is similar to phosphorus in this regard because they both have five valence el...

MadisonB

It is harder to remove the second electron and ever harder to remove the third due to an increase in effective nuclear charge when electrons are removed. The effective nuclear charge is a positive force attracting valence electrons. Therefore, when one electron is removed, the same amount of positiv...

MadisonB

As a general rule, things become more complicated in terms of an expanded octet 3rd row and down, and the first few elements are stable with only two electrons. I found a more cut and dry rule for octet rule exceptions at this link: https://saylordotorg.github.io/text_general-chemistry-principles-pa...

MadisonB

You bond the atoms where there is either an excess or lack of valence electrons, you know this by placing the electrons in the structure or by visualizing it. The following are two helpful links with step-by-step instructions: http://www.chem.ucalgary.ca/courses/350/Carey5th/Ch01/ch1-3depth.html htt...

MadisonB

Final state - Initial state

We talked about how this is not always so, but for the most part, this is the correct way of thinking about it.

MadisonB

Another explanation for this is that the most balanced state might not be the one that goes in order with the set rules. Lower energy fills before higher energy, and the most balanced state is strived for as well.

MadisonB

You'll still have to know unit analysis and other basic concepts from Test1, but the general concepts tested will be everything up until lecture Friday.

MadisonB

I've heard various things like before lecture Friday or Sunday night. My TA told me to just get it done by Thursday night to be safe.

MadisonB

It's probably a lot like the equation sheet on the front on test 1, which you should have.

MadisonB

I believe this is because "l" has to be n-1. n=the first quantum number, and l=the second quantum number.

MadisonB

You always look to the least amount of sig figs in any problem. It makes practical sense because the least number of sig figs determines how precise you can be in your calculations.

MadisonB

We haven't gone over it in class yet, but there are a series of procedures for writing the names of chemical formulas. If you are curious, this is a website that goes over how to write chemical formulas: http://www.kentchemistry.com/links/nami ... riting.htm

MadisonB

They can both be used (and are basically the same thing), but make sure that all units cancel when you reach the end of the problem.

MadisonB

I usually start with what occurs the least and work through trial and error if I have to. It something is taking too long or not working out make sure you wrote it down correctly because a small mistake at first can turn into a huge hassle in the long run.

MadisonB

To get you started, you will be using the equation M1V1=M2V2, to calculate what you are missing. This link is for a helpful youtube video on dilution: https://www.youtube.com/watch?v=v6dnEp58mVk

MadisonB

When rounding for sig figs with a number that ends in a five, do you round up or round down? Does it depend on whether it is preceded by an even or odd number? For example, does the number 2.65 for two sig figs go to 2.7 or 2.6? thanks

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