CHEMISTRY COMMUNITY

lindsey_ammann_4E

It's cumulative, but I would focus more on the newest topics and topics that were not heavily covered on the midterm and two tests.

lindsey_ammann_4E

i find this diagram pretty helpful in determining order: (shows zero, first, and second order graphs respectively)

lindsey_ammann_4E

here are the graphs for zero order, first order, and second order, respectively

lindsey_ammann_4E

We should be prepared to find, for the purposes of this class, the zeroth order, first order, and second order. There are orders higher than that, but they are rare and we are not expected to do calculations involving those.

lindsey_ammann_4E

The above responses are correct. You can think of dividing the units by moles as you move up to the next order.

lindsey_ammann_4E

I like Lyndon's and Karen's because they have worksheets you can practice.

lindsey_ammann_4E

We are not technically using the Van't Hoff Equation, we are using a derivation that is useful for the purposes of this class.

lindsey_ammann_4E

We never have to be able to completely derive an equation, only manipulate one and solve it.

lindsey_ammann_4E

We don't need to know how to derive it, only to manipulate/solve it.

lindsey_ammann_4E

If given degrees Celsius, convert to K.

lindsey_ammann_4E

Eva Guillory 2E wrote:

What do exergonic and endergonic mean?

lindsey_ammann_4E

You know a reaction is spontaneous when delta G is negative. If it's positive, the reaction is not spontaneous.

lindsey_ammann_4E

Delta H is equal to q at constant pressure, whereas delta U=q+w.

lindsey_ammann_4E

Work is interpreted as energy used in the process of compression or expansion of a system. This means the value of work changes when the volume changes. For this reason, w=0 when there is no compression or expansion.

lindsey_ammann_4E

If they ask for the change in internal energy, give your answer in J or kJ.

lindsey_ammann_4E

We will be given the curve if we need the values to solve a problem. Lavelle never makes us memorize constants.

lindsey_ammann_4E

Other than pure visualization, there is no shortcut.

lindsey_ammann_4E

Condensation is exothermic.

lindsey_ammann_4E

I know phase changes from liquid to vapor, solid to liquid, and solid to vapor are always endothermic. Would the opposite phases changes (vapor to liquid, and liquid to solid) always be exothermic? Yes, you are correct. In the first changes you listed, heat acts like a reactant. This means the reac...

lindsey_ammann_4E

To answer this question, you must refer to the heating curve. In this case, steam has more energy in Kj/mol, meaning it will burn your hand more upon contact due to the higher amount of energy of vaporized water (compared to the lower amount of energy in liquid water).

lindsey_ammann_4E

When a molecule is in its most stable state, the standard enthalpy of formation equals 0.

lindsey_ammann_4E

When a reaction is endothermic, think of heat as a reactant.
When a reaction is exothermic, think of heat as a product.

lindsey_ammann_4E

This is similar to when we discuss endothermic or exothermic reactions. If heat is added or removed, the equilibrium shifts. However, heat is not included in K. Same goes for water in this example.

lindsey_ammann_4E

This is because the stoichiometric coefficients/ratio are the same on each side, meaning it won't favor either side.

lindsey_ammann_4E

Meigan Wu 2E wrote:On Worksheet 2, why is the concentration of CO3 the same as Ka2 for problem 4b?

^ I have the same question

lindsey_ammann_4E

Stability is based on whether the reaction favors the products. A more stable reaction would favor the products, making the K value larger.

lindsey_ammann_4E

For the effect of something like pressure, use the ideal gas law PV=nRT. Increasing something on one side will increase something on the other side.

lindsey_ammann_4E

Anything that's not too far off base from what we've learned so far is good. This all relates to chemical equilibria.

lindsey_ammann_4E

haleyervin7 wrote:For purposes of calculation, do we always assume it is an ideal gas?

For the purposes of this class, we need to assume that a gas is an ideal gas in order to use the idea gas equation. If the problem requires calculations, it's safe to assume it's an ideal gas.

lindsey_ammann_4E

A similar way to think about it is that if K>10^3, the reaction favors the products. If K<10^3, the reaction favors the reactants.

lindsey_ammann_4E

When they give you values in bars, use Qp. When they give you values in M (mol/L), use Qc.

lindsey_ammann_4E

Not sure if we have to answer that directly, yet it's good to know for problem solving and checking your answer.

lindsey_ammann_4E

Yes, you only add -ate if the whole compound is negative.

lindsey_ammann_4E

Saman Andalib 1A wrote:You name the ligands in a coordination compound in alphabetical order.

To follow up, is it alphabetical order by prefix or by the names of the ligands?

lindsey_ammann_4E

Maggie Pickford 3F wrote:So what exactly is paramagnetism and diamagnetism?

Paramagnetic means that there is only one electron in the subshell, whereas diamagnetic means that two electrons are paired (with opposite spin) in the same subshell.

lindsey_ammann_4E

ariellasarkissian_3H wrote:Also, are we responsible for memorizing the bond angles for each shape?

Yes, he mentioned that you must memorize the VSEPR shapes and their bond angles.

lindsey_ammann_4E

This is because a hybridization gives the molecule a lower energy state than if it were unhybridized. This makes it more stable.

lindsey_ammann_4E

The d orbital exists when there is an expanded octet.

lindsey_ammann_4E

We are only expected to draw the Lewis structures as we had done so before. He just wants us to be able to identify the geometry (VSEPR model) by looking at the Lewis structure. We are not expected to draw the VSEPR model ourselves.

lindsey_ammann_4E

It doesn't matter which atoms for which the bonds you make bold or dashed if the bonds are symmetrical with that shape because the structure can rotate. It's just a different view.

lindsey_ammann_4E

Here's a way I like to think about it:
single bond- longest, weakest
double bond
triple bond- shortest, strongest

lindsey_ammann_4E

For reference, there is a figure in the electronegativity section showing the electronegativity values on the periodic table. However, for the test, just know that the further apart elements are on the periodic table, the greater difference in electronegativity they will have.

lindsey_ammann_4E

The electronegativity values are experimentally calculated. There is a chart in the book that lists electronegativity values, so you can just use that. As a general rule, elements further apart on the periodic table will have a higher difference in electronegativity.

lindsey_ammann_4E

Fluorine is kind of an exception to the general rule of electron affinity. Typically, you would expect F to have a higher electron affinity since it is higher in the group than Cl. F is very small though, so there is electron-electron repulsion when you add a new electron because there are already e...

lindsey_ammann_4E

Finding the oxidation number of each element in a molecule gives you the formal charge of each element and subsequently that of the whole molecule.

lindsey_ammann_4E

Radicals have one unpaired, lone valence electron. They are very unstable and don't exist long by themselves in nature.
Here's an example of what it looks like and how you would draw it:

lindsey_ammann_4E

Most stable/lowest energy are essentially the same in this context. As for the structures, if you compare two separate structures that have different formal charges assigned, the one with the formal charge closest to zero would be considered most stable/lowest energy.

lindsey_ammann_4E

We only need to know what he lists on his lecture outlines on his website for 14A. I would check the Chemical Bonds outline!

lindsey_ammann_4E

The exceptions start in the second row of the p-block, and continue in the rows of the p-block below that.

lindsey_ammann_4E

remember that ionic bonds do not share electrons!

lindsey_ammann_4E

For me, it helps to use the bonfire metaphor that Dr. Lavelle mentioned in lecture. Let's say you're an electron sitting close to the fire. If another person (another electron) sits or stands in between you and the fire, then you will feel less heat (or attraction) to the fire (nucleus). In a sense,...

lindsey_ammann_4E

Additionally, in general the elements in the top right of the periodic table have a higher electron affinity. So by this general guideline, carbon would have a higher electron affinity.

lindsey_ammann_4E

Does anyone know with certainty that we will be given the mass of an electron on the test?

lindsey_ammann_4E

To add to the previous response, we will only be given the equations for E=hv and c=λv, which we must combine to produce E=hc/λ on the test.

lindsey_ammann_4E

As far as I know, the electrons must still jump up or down an energy level, but there is the same energy difference between each. So absorption would be +eV, and emission would be the same amount but -eV.

lindsey_ammann_4E

Light hits a sodium metal surface and the velocity of the ejected electron is 6.61 x 105 m.s-1. The work function for sodium is 150.6 kJ.mol-1. Will someone walk me through this? 30. C. What is the frequency of the incident light on the sodium metal surface? A. 3.01 x 1014 Hz B. 2.27 x 1038 Hz C. 4....

lindsey_ammann_4E

Light hits a sodium metal surface and the velocity of the ejected electron is 6.61 x 105 m.s-1. The work function for sodium is 150.6 kJ.mol-1. Will someone walk me through this? 29. B. How much energy is required to remove an electron from one sodium atom? A. 2.501 x 10-22 J B. 1.506 x 105 J C. 2.5...

lindsey_ammann_4E

Light hits a sodium metal surface and the velocity of the ejected electron is 6.61 x 105 m.s-1. The work function for sodium is 150.6 kJ.mol-1. Will someone walk me through this? A. What is the kinetic energy of the ejected electron? A. 3.01 x 1025 J B. 3.98 x 10-19 J C. 7.96 x 10-19 J D. 1.99 x 10-...

lindsey_ammann_4E

During lecture, Dr. Lavelle mentioned that we would always be given the periodic table on tests (even when we do not need it) so that we can feel comfortable. I am assuming he was referring to not only the midterm and final but the discussion quizzes/tests as well.

lindsey_ammann_4E

1. Add up the coefficients of each side of the equation (this gives you the total amount of moles on each side).
2. Find the difference in moles on each side (subtract the total moles of products from the total moles of reactants).

lindsey_ammann_4E

Essentially, when they are asking for the amount of molecules, they are referring to an element or something covalently bonded (think Na or O2). When they are asking for the amount of formula molecules, they are referring to an ionic compound (NaCl). You must use Avogadro's number for both situation...

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