CHEMISTRY COMMUNITY

Veronica_Lubera_2A

Along with the final, there will probably be information too about the review sessions and office hours in an upcoming email.

Veronica_Lubera_2A

As a last result: If you can't get your test back try asking some friends who had their discussion on Tuesday and look at the answers?

Veronica_Lubera_2A

Thank you Lyndon so much for your kindness and compassion when teaching chem 14A/B to us!! We didn't know it at the time, but we were all looking for someone to relate difficult concepts and share funny jokes during workshops. Keep working hard and we will always support you!

Veronica_Lubera_2A

I would just send pictures of the homework to them just in case.

Veronica_Lubera_2A

I think we'll know by tomorrow with an email announcement.

Veronica_Lubera_2A

For the log equation you use it at standard conditions (25 degrees celsius) and the lnQ equation can be used in any situations. My personal preference is the lnQ equation since you can still get the same answer as the log one and don't have to worry about knowing when to apply it.

Veronica_Lubera_2A

Yes I think H2O is the only one left out.

Veronica_Lubera_2A

Now in cases where you don't need Pt(s) is when you already have a conductive solid metal in the solution.

Veronica_Lubera_2A

When you find the half reactions, n is the least common multiple of their shared electrons. So you would have to balance them. (Usually n is either 1 or 2).

Veronica_Lubera_2A

Yes so you would find the half reactions and balance them to find the least common multiple of their transferred electrons in the final equation. (Usually it's 1 or 2 in the electrons transferred.)

Veronica_Lubera_2A

Van't Hoff's Equation along with the Nernst Equation we should know how to derive and calculate both.

Veronica_Lubera_2A

Van't Hoff's equation is:

ln(K2/K1)= (-DeltaH/R)(1/T2 - 1/T1)

So the equation relates enthalpy too but this value should be given in the problem.

Veronica_Lubera_2A

You need 2 formulas:

1. DeltaG=-nFE*
2. DeltaG=DeltaG* + RTlnQ

Combine rections:
-nFE(cell)=-nFE*(cell)+RTlnQ
Therefore,
E(cell)= E*(cell)-(RT/nF)lnQ

It is also important to know that at 25 degrees C (so standard conditions),

E(cell)= E*(cell) - (0.0592V/n)logQ

Veronica_Lubera_2A

When you write the half reactions, you need to have the solid in the equation because it is in its most stable form (gain of electrons to eliminate the +1 and +3 charge in Au). When we are writing the cell notation, we still need to include the solid since it is in our half reactions with a bar sepa...

Veronica_Lubera_2A

The Van't Hoff equation relates K with temperature. K1 corresponds with T1 and K2 corresponds to T2.

Veronica_Lubera_2A

Also keep in mind that n is the number of moles of electrons being transferred in a half reaction, not the total amount of the two balanced reactions.

Veronica_Lubera_2A

Ecell= E*cell- (RT/nF)lnQ. When a redox reaction is at equilibrium, DeltaG=0, Q=K, and there is no net transfer of electrons. When there is no net change in the number of electrons, Ecell=0 and then our equation turns into E*cell=(RT/nF)lnQ. So yes, Ecell will decrease to reach 0 but also keep in mi...

Veronica_Lubera_2A

Gases have the highest entropy possible because they take up a lot of space (volume) and can be arranged in multiple positions because of their high speed and free movement. Therefore, option A only had the option of a gas in the products.

Veronica_Lubera_2A

When determining the number of electrons to place on a side, you have to compare the overall charge on the left and right sides. Generally, let's say for example, there is a higher positive charge on the left side, you would add that number of electrons on the right side to balance the difference in...

Veronica_Lubera_2A

They also correlate with the fact that Temperature affects K, so each K1 would correspond directly to that T1.

Veronica_Lubera_2A

At equilibrium, DeltaG=0 because the forward and backward reaction rates are equal. So the formula for nonstandard conditions (including not at equilibrium) is Delta G= DeltaG* + RT lnQ, where Q is the reaction quotient ([Products]/[Reactants]). At equilibrium, the Q variable would become K.

Veronica_Lubera_2A

And when Delta U=0 then q=-w.

Veronica_Lubera_2A

You should always check the units in the constants you plug into your formulas. So it would depend whether it's joules or kilojoules.

Veronica_Lubera_2A

These are just a few but at constant pressure, q=DeltaH and w=-PDeltaV
At constant volume, w=0 and you can evaluate the formulas using this information.

Veronica_Lubera_2A

Delta s=q/T is used when there is a constant temperature. q=DeltaH is used when there is a constant pressure. Q is heat which is separate from Gibbs free energy.

Veronica_Lubera_2A

Under the 14B website, there is a list of constants and equations sheet. I believe that the general ones are on there but you have to memorize/know how to derive the more specific ones with changes in volume/temperature.

Veronica_Lubera_2A

Entropy at the molecular level means having more 'microstates', or different ways of arranging atoms. Complex molecules have more atoms, and therefore, more places you can change its composition.

Veronica_Lubera_2A

Since molecular weight can be similar between different gases, it would be reasonable to assume that degeneracy can truly distinguish them apart better.

Veronica_Lubera_2A

I wouldn't say they're dependent on the number of bonds but rather on the different placements of atoms (like how many positions they can take). Octahedrals would definitely have more microstates than a tetrahedral, for example.

Veronica_Lubera_2A

Usually I think we will be given linear molecules in terms of symmetry since they are common ideal gases such as CO2 and O2.

Veronica_Lubera_2A

Yes, in expansion there will be a negative sign because the system is losing energy.

Veronica_Lubera_2A

Yes, usually when a system gains heat, q will be a positive value.

Veronica_Lubera_2A

When a system expands, you should get a negative answer for work. When a system is compressed, you will get positive work.

Veronica_Lubera_2A

When the pressure is constant, you can also get DeltaU=DeltaH-P(Delta V) from the general formula DeltaU=q+w.

Veronica_Lubera_2A

Also another derivation of the formula we learned in class today was DeltaU=DeltaH-P(DeltaV) if the pressure is constant.

Veronica_Lubera_2A

Reactants will have a - sign, products will have a + sign. Look for the coefficients in a reaction and that will determine whether you will have a +-2x if you have a 2 moles of that certain element or just a +-x for 1 mol.

Veronica_Lubera_2A

Yes, Dr. Lavelle said you can still turn in HW problems from the second week in discussions.

Veronica_Lubera_2A

I think you're mentioning solubility rules so you don't include groups 1 and 2 in the reaction because they don't affect pH (totally dissolve in water and are present on both sides of the reaction so you can cancel them out). Example is NaOH and also salts like NaCl don't affect pH. Conjugate bases/...

Veronica_Lubera_2A

It has to be less than so anything 10^-4 and smaller.

Veronica_Lubera_2A

So the shortcut is that whenever you increase volume (by decreasing pressure), you shift the equilibrium to the side with more moles of gas. The technical version is that you actually change concentrations using the PV=nRT formula and n/V is concentration (Molarity). If volume changes (with the conc...

Veronica_Lubera_2A

I went to his office hours and he said the first test will cover the first two units. I would definitely do all of the hw and understand the ice tables for weak acids and bases. Also looking over the notes and the examples he used in class.

Veronica_Lubera_2A

A good mnemonic to remember this is BARF which stands for Breaking-Absorbing; Release- Form. So breaking bonds needs to absorb energy and forming bonds releases energy.

Veronica_Lubera_2A

I think that for when calculating pH, you can drop the negative in the final answer to get 0.18 pH from 1.5 M H3O+ instead of -0.18 M.
So from that you get pOH by doing 14-0.18=13.824.
And the concentration of OH- is 10^-13.824 which equal 1.5*10^-14.

Veronica_Lubera_2A

Today in lecture he mentioned that 10^-4 is the boundary, so anything 10^-4 and smaller can be approximated. However, he said that if K does equal 10^-4, you should double check your answer at the end (by plugging it back in) to see if there is a difference between your answer and the given because ...

Veronica_Lubera_2A

So the equation is PV=nRT. An example of using this problem is when we are given pressures and must find Kc. You would have to use the formula to convert to concentrations (n/V) of each individual molecule, then plug it into the Kc formula.

Veronica_Lubera_2A

Also B is incorrect because the equilibrium constant gives us the RATIO of concentrations of products vs. reactants- we cannot calculate their exact rates. C is incorrect because it's irrelevant at the moment- activation energies relate more to the thermodynamic unit.

Veronica_Lubera_2A

When you add an inert gas like Helium, (which is NOT needed for the reaction), there will be no effect on the equilibrium constant because there is no change in concentration.

Veronica_Lubera_2A

The same rule applies of omitting solids in the equilibrium constant.

Veronica_Lubera_2A

I feel as though they would be given in the problem but make sure to check if the reaction is balanced.

Veronica_Lubera_2A

K is when the reaction reaches equilibrium. Q is a specific point in time before reaching equilibrium. We often compare Q to K; for example if Q<K then the reaction will shift to the right.

Veronica_Lubera_2A

How do you identify them?

Veronica_Lubera_2A

So when naming in alphabetical order, you look at the element/compound described, not the prefix. So in your example, you would put chloro first.

Veronica_Lubera_2A

Some common polydentates to recognize are ethylenediamine and its longer chains such as DIEN and EDTA. Another example is oxalate because they can bind in multiple places.

Veronica_Lubera_2A

Strong acids dissociate completely. When going down a group, the atoms are getting larger (making a bond longer), and therefore making the bond weaker. Therefore, the strength will increase because the bond is easier to break.

Veronica_Lubera_2A

SO4-2 is sulfate, (so it has a -2 charge).

Veronica_Lubera_2A

Yes but it includes some equations we haven't covered yet.

Veronica_Lubera_2A

There are significantly more weak acids than strong acids. Weak acids have lower Ka, so larger pKa, meaning they will dissociate more. In class today, he said HI is a strong acid because I is less electronegative and larger, meaning that the bond is longer (weaker) and it will be easier to break. In...

Veronica_Lubera_2A

After going through the examples given in the book, I don't think there is a difference when going from the name to writing the compound. One potential pattern that I found was that the more positive charge was placed first, but I don't think this significantly matters. Ask your TA though just in ca...

Veronica_Lubera_2A

The coefficient in front of the hybridization is the row number. That is why when C is in the second row, it has a 2 sp2 bond hybridization. An example with sp3 hybridization is H2O: the Oxygen will have 2sp3 hybridization because it is in the second row and has 4 regions of electron density (2 sing...

Veronica_Lubera_2A

Single, double, and triple bonds all represent one region of electron density. Therefore, sp hybridization has 2 regions of electron density, sp2 has 3 regions of electron density, sp3 has 4 regions, sp3d has 5 regions, and so on.

Veronica_Lubera_2A

Strong acids and bases will dissociate completely (acids into H3O+ and based into OH-). There are 7 main strong acids. Strong bases are comprised of Group 1 and 2 oxides/hydroxides (use the periodic table).

Veronica_Lubera_2A

Why is [Ni(CN)4)]2- tetracyanidonickelATE? Why does it end in -ate instead of just nickel?

Veronica_Lubera_2A

Single bond: 1 sigma bond
Double bond: 1 sigma, 1 pi bond
Triple bond: 1 sigma, 2 pi bonds

Sigma bonds form when orbitals overlap end to end.
Pi bonds form when orbitals overlap side by side.

Veronica_Lubera_2A

Also every molecule will have London dispersion (induced dipole-induced dipole) forces present.

Veronica_Lubera_2A

The molecule with more hydrogen bonds will be stronger. But you can also argue the molecule with stronger London dispersion (induced-induced dipole) forces will be stronger overall. Strong dispersion forces means that the atom compared is bigger (so more electrons), so larger polarizability, and the...

Veronica_Lubera_2A

Alpha stands for polarizability and r stands for distance. So, intermolecular forces depend on the strength of an atom to distort electrons as well as how far the two atoms/molecules are away from each other.

Veronica_Lubera_2A

Cations have polarizing power while anions have polarizability. The definition of polarizability is the ability to distort electron clouds. For cations, those that are smaller and highly charged are the most polarizable. For anions, those that are bigger and less charged are the most polarizable. In...

Veronica_Lubera_2A

Usually anything on the far left compared to the far right (fluorine) of the periodic table will have the highest EN difference.

Veronica_Lubera_2A

Also the best way to think about the shapes is to visualize them. The most stable shapes with have electron densities symmetrically arranged around the central atom that will result in the least amount of repulsion.

Veronica_Lubera_2A

With the shapes, I think it’s also important to know the bond angles associated with them. (Ex. 109.5 degrees for a Tetrahedral).

Veronica_Lubera_2A

I feel if you truly love chemistry and are willing to put in more effort to understand the concepts thoroughly to succeed in both classes, you can take both at once. Otherwise, if you need more time to process the new material I would hold off until the Spring quarter.

Veronica_Lubera_2A

Yes usually each molecule will have London (dispersion) forces.

Veronica_Lubera_2A

Yes, usually Delta X is the diameter of the atom. So this means if they give you radius, you have to multiply by 2 to get the diameter. Also remember units have to be in meters so convert if necessary.

Veronica_Lubera_2A

What did the chemical agent say?

My name is Bond, Ionic Bond. Taken, not shared.

Veronica_Lubera_2A

When energy is absorbed, Delta E is positive. This means the atom is going from a lower quantum energy state to a higher one. For example, going from n=1 to n=3.

Veronica_Lubera_2A

Delta X is uncertainty in position (in meters, usually the diameter value of the atom) and Delta P is uncertainty in momentum. Delta P= m x DeltaV, so you can further solve for the uncertainty in velocity.

Veronica_Lubera_2A

Yes, for example in KF. F is extremely electronegative, so it will pull electron's closer making it more negatively charged. Therefore, the K will be more positively charged and a dipole moment will occur.

Veronica_Lubera_2A

When a question asks for the most stable resonance structure, you have to draw the different lewis dot structures (only switching the placement of bonds) and calculate formal charges. The ones closest or equal to 0 will be the most stable and therefore be the answer.

Veronica_Lubera_2A

Essentially elements can disobey the octet rule in two ways: 1. They can break it by their massive size and extra space of a d-block. (3 row periodic table and below) 2. They don't reach their 'full potential' of the octet rule because of a high ionization energy. (Ex: BF3; Boron will only have 6 va...

Veronica_Lubera_2A

What also helps me remember that the d block comes before the s block in the electron configuration is that the leading coefficients of d and the blocks before it are the same. For example, 3s2, 3p6, 3d10 (3 is the same) and afterwards, the 4th shell begins.

Veronica_Lubera_2A

In the formula, instead of using S/2 I just count the number of bonds with that atom and you get the same answer. I think it's a little bit easier since you don't have to divide by two and can subtract that exact number.

Veronica_Lubera_2A

What is the difference between delocalization and resonance? Does one lead to the other?

Veronica_Lubera_2A

What are the properties of metals, nonmetals, and metalloids? Also which one loses electrons more easily?

Veronica_Lubera_2A

Yes- it will be helpful when recognizing ionic (metal and nonmetal sharing electrons) or covalent bonds (between two nonmetals). Also it's good to keep in mind their valence electrons for when we will be drawing their Lewis Dot Structures.

Veronica_Lubera_2A

I also asked my TA and she said it would be 6. There was some confusion because the answer key was wrong for one of the homework questions but it should be double the +- value.

Veronica_Lubera_2A

For homework question 1E.25, it asks for the valence shell configuration of metals. So for example, the Group 5 transition metals are (n-1)d^3ns^2. Can someone please explain what these numbers/orbitals mean in the context of the problem?

Veronica_Lubera_2A

One helpful tip that helps me remember Ionization Energy increasing along the period is that F (Fluorine) is considered to be the strongest element its ability to remove electrons. So if you just keep in mind that Fluorine is the best, then you can think of the trends more easily.

Veronica_Lubera_2A

An equation that you could separate from the rest is DeBroglie's equation, which is only used for particles (electrons/protons/neutrons).

Veronica_Lubera_2A

Delta V is the uncertainty of its position. So for example, if in the given we have 10 m/s +- 1m/s, the delta V would be 1. It's 1 and not 2 because a particle can't go in two directions at once.

Veronica_Lubera_2A

The p, d, and f orbitals also have a nodal plane where there is zero electron density (and therefore zero electron probability.) There is a trend to how many 'petals' you draw on the axes as well: S is just a circle because of its symmetric electron distribution. P has 2 horizontal petals. D has 4 p...

Veronica_Lubera_2A

Also black bodies are mainly found in physics, so there shouldn't be a large emphasis on these.

Veronica_Lubera_2A

Dr. Lavelle said that we should most be familiar with the s,p, and d orbitals since they contain elements in biological systems. (The elements towards the bottom of the periodic table are toxic and the last ones are even radioactive). Locations you have to memorize/relatively know placement of: S or...

Veronica_Lubera_2A

How would you solve this problem?

A lamp rated at 32W (1 W= 1 J/s) emits violet light of wavelength 420nm. How many photons of light can the lamp generate in 2 sec? How many moles of photons are emitted in that time interval?

Veronica_Lubera_2A

Also within the next few weeks, we will cover nomenclature in class where we will learn all of the rules.

Veronica_Lubera_2A

I asked one of the T.A.'s this question and he said that as long as in the steps of your calculation, you use more decimals than the required amount of sig figs, then you should be able to receive the correct answer when rounding at the end.

Veronica_Lubera_2A

Delta E will have a negative value when the electron is emitted (decreased energy) and positive sign when the electron is absorbed (increased energy). Energy in itself is always a positive value.

Veronica_Lubera_2A

In essence, Rydberg formula is best used to find the frequency between energy levels and is derived from the energy formula of En=-hR/n^2. Use the energy formula when you want to find the energy at a specific energy level or the difference of energy levels (where you would use Energy(final)-Energy(i...

Veronica_Lubera_2A

How would you solve this question? Specifically, the energy per one photon of radiation? The meter was defined in 1963 as 1,650,763.73 wavelengths of radiation emitted by krypton-86 (it has since been redefined). What is the wavelength of this krypton-86 radiation? What energy does one photon of thi...

Veronica_Lubera_2A

Use the uncertainty of velocity (delta v= 3.4E10) to calculate the electron's uncertainty in kinetic energy. Then, calculate the uncertainty in kinetic energy per mole of electrons (that is, per mole of hydrogen atoms).
Mass of electron is 9.1E-31 kg.

Veronica_Lubera_2A

The hydrogen atom has a radius of approximately 0.05 nm. Assume that we know the position of an electron to an accuracy of 1% of the hydrogen radius, calculate the uncertainty in the speed of the electron using the Heisenberg uncertainty principle. So the correct answer is Delta V >= 10^8 m/s. How w...

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