CHEMISTRY COMMUNITY

Xinyi Zeng 4C

Lynsea_Southwick_2K wrote:What section covers deprotonation?

Just to add on to the previous reply, it is covered in the acid-base equilibrium section. It is related to the definition of acids and bases with respect to loss/gain of hydrogen.

Xinyi Zeng 4C

For the snowflakes, delta H is negative because the snowflakes lose heat, and delta S is negative because going from a liquid to a solid is less chaotic. Negative delta H minus a negative delta S makes a negative delta G. For the sublimation, delta H is positive because heat is going in, and delta ...

Xinyi Zeng 4C

It is equal to zero when neither the forward or the reverse reaction is favoured. The reaction proceeds until equilibrium is reached.

Xinyi Zeng 4C

The order of reaction is the power of the reactant's concentration term in the rate equation. Therefore, for a first-order reaction, rate=k[A]^1=k[A]; while for a second-order reaction, rate=k[A]^2; so on and so forth for third-order, fourth-order or fifth-order reaction. As the order of reaction di...

Xinyi Zeng 4C

Just to add on, the order of reaction is the power of the reactant's concentration term in the rate equation.
Therefore, for zero-order reaction, rate=k[A]^0=k, as [A]^0=1; while for first-order reaction, rate=k[A]^1=k[A].

Xinyi Zeng 4C

They are the same thing! ln([A]t/[A]0)=−kt can be written as ln([A]t)-ln([A]0)=-kt [ according to the log rule that ln(a/b)=ln(a)-ln(b) ] multiply both sides of the equation by -1, you will get: -ln([A]t)+ln([A]0)=kt, hence ln([A]0)-ln([A]t)=kt applying the log rule again, you will get ln([A]0[A]t)=kt

Xinyi Zeng 4C

They are two different things. The oxidizing agent will be reduced, as it will oxidize the other thing that is involved in the redox reaction. That's why it is an "oxidizing agent". If a thing is oxidized, it means that it is a reducing agent, as the other thing in the redox reaction will ...

Xinyi Zeng 4C

You definitely need to know how to write the cell diagram, and they won't ask you to draw an actual setup as what's in the slides during lecture.

Xinyi Zeng 4C

Dr Lavelle gave a detailed explanation for how to write the cell diagram in this post: https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=140&t=43085 He did not mention the sequence of the ions in the same phase, so I think both are fine! The more important things to take note of are probably i...

Xinyi Zeng 4C

Yes, and Faraday's constant will be given on the tests and exams. I think so far we will only need to apply this concept for the equation delta G = -nFE

Xinyi Zeng 4C

Just to add on, the salt bridge prevents direct mixing but allow passage of ions between the two half-cells, competing the electrical circuit!

Xinyi Zeng 4C

I think they bot allow ion transfer and both can serve the same functions for galvanic cell. The question should specify which one to use!

Xinyi Zeng 4C

Just to add on, delta G (without knot) is calculated from delta H - T * delta S, while delta G knot is calculated from delta H knot - T * delta S knot. You can use delta G's equation to predict the effect of temperature and feasibility of a reaction, sometimes by just knowing the signs of delta H an...

Xinyi Zeng 4C

Just to add on, you wouldn't really say if delta G is spontaneous or not.
The sign of delta G denotes whether the reaction/process is feasible or can take place spontaneously.

Xinyi Zeng 4C

There was a similar question in the Post "Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)", and Karen explained why we are using Cv instead of Cp: "You use Cv when calculating the temperature change because you are ignoring the change in volume for that part. So, in this ques...

Xinyi Zeng 4C

I think it depends on which direction you are looking at? If the heat is lost from the system to the surroundings, then the system's change in enthalpy should be negative while the change in enthalpy of the surroundings should be positive, vice versa. One thing for sure is that if the reaction relea...

Xinyi Zeng 4C

Ideal gas and noble gas are two different concepts. The concept of "Ideal gas" based on several basic assumptions (e.g. the gas particles have negligible volume/size compared to the volume of the container; the gas particles exert negligible intermolecular forces on one another). "Ide...

Xinyi Zeng 4C

Just to add on, I think it really depends on what the question asks. Sometimes the question will ask you to convert the pressure to a certain unit, and that's when there is a requirement for the unit used.

Xinyi Zeng 4C

This equation if the Ideal Gas Law and relationships between the different variables could be derived from this equation: Boyle's Law: at constant T and n, V and p have an inverse relationship (pV = constant), p1V1 = p2V2 Charles' Law: at constant p and n, V and T have a direct relationship (V/T = c...

Xinyi Zeng 4C

Just to add on, "enthalpy of bond" has a more formal name as "Bond Energy" and its definition is the amount of energy required to break that particular bond. Breaking of bond requires energy and hence is endothermic.

Xinyi Zeng 4C

Heat capacity of the calorimeter refers to the heat required to raise the temperature of that calorimeter by 1 degree. In this question, 22.5kJ of heat is required to raise the temperature of the calorimeter from 22.45 to 23.97 (by 23.97-22.45=1.52 degrees). Hence, to find its heat capacity, just di...

Xinyi Zeng 4C

All the constants and equations that we will use during the test/exam can be found on the website, the link is right here: https://lavelle.chem.ucla.edu/wp-conten ... ations.pdf

Xinyi Zeng 4C

Diatomic molecules are molecules composed of only two atoms, and the two atoms can be of the same or different chemical elements. The reason that the bond energy of C-C is not as accurate is because there is no such thing as C2, and C-C bond energy is calculated as an average of bond energy of C-C i...

Xinyi Zeng 4C

I'm in Lecture 4 and we just went through Hess's Law today during the 3pm lecture. Hess's Law states that enthalpy changes are additive (since enthalpy is a state function). Therefore, enthalpy at each step of a multi-step reaction can be added to give the total enthalpy change.

Xinyi Zeng 4C

Just to add on, Ka and Kb are used for weak acids and bases only, as strong acids and bases will fully dissolve.

Xinyi Zeng 4C

It will be better if you memorize the common strong acids and bases (and I think that we are supposed to do so), then the rest will usually be weak acids. Some common weak acids are those organic acids like HCOOH, CH3COOH, HNO2; and examples of weak bases are NH3 and amines

Xinyi Zeng 4C

We only use Kp when the reaction system is at equilibrium, other than that, we will always calculate Q and compare it with Kp (or sometimes Kc if the question is about concentrations) to see which direction (products or reactants) the reaction will move towards. Hope this helps :)

Xinyi Zeng 4C

Should we specify Qc And Qp just like we differentiate between Kc and Kp? I think so, but if the question focus on pressures only or on concentrations only, just write Q or K should be fine. Just make sure you use the correct formula, do not write pressures of reactants/products for Kc/Qc and do no...

Xinyi Zeng 4C

amogha_koka3I wrote:Is it the same case for liquids as it is for solids?

Yes, it should be the same case in this example, as liquid don't contribute much towards pressure like solids.

Xinyi Zeng 4C

Try to write out the expression for Kc=[BrCl]^2/([Br2][Cl2]), and then sub in the values for Kc and concentrations of BrCl and Cl2. I got my answer this way.

Xinyi Zeng 4C

-F is the most electronegative hence most electron-withdrawing, so it will pull the electrons in the COOH group towards itself, hence it will be easier for it to lose H+ and it is the most acidic. -CH3 group is the most electron-donating and least electron-withdrawing, hence it is harder for it to l...

Xinyi Zeng 4C

Not really, some positively charged ion can donate electron pairs and be acidic, too, it's just that it will be harder to donate electron pairs than accept electrons sometime. Therefore, you have to look at the specific interaction happening to determine whether the species is going to donate electr...

Xinyi Zeng 4C

To determine which one is a stronger base, you need to look at the availability of the lone pairs for donation. Therefore, those atoms without resonance and less electronegative atoms with lone pairs are usually stronger base by Lewis definition, as the lone pair can be more easily donated. But if t...

Xinyi Zeng 4C

For part d, KBr, KOH is a strong base and HBr is a strong acid, so the KBr salt solution is neutral as both K+ and Br- are hydrated and no hydrolysis happens, so no extra OH- or H3O+ will be formed. For AlCl3, first of all, Al3+ will separate itself from Cl− in water, due to the nature of this salt....

Xinyi Zeng 4C

Both definitions apply to different acids and bases. Note that there is a limitation to the Bronsted theory as it does not count for the acidic properties of substances that do not have any hydrogen atoms, and this is a good time to use Lewis definition than Bronsted definition.

Xinyi Zeng 4C

I feel that in the Bronsted definition, it did not specify that the acid/base must be in aqueous form, as the definition of acid if "a substance that can donate a proton to another substance". So the important thing is that it can donate a proton.

Xinyi Zeng 4C

Andrew Sun 1I wrote:If an acid is an electron acceptor, whilst giving away the H+ (which is essentially a proton), how does it take in another electron? or does the electron already exist to the acid?

I think the electrons that the acid is going to accept will come from the base that is donating the electron.

Xinyi Zeng 4C

If I understood your question correctly, you are asking why the bond angle of sp3 is smaller than that of sp2 and than that of sp? If this is the question, I feel that it is because they have different type of hybridization, which means that they have different regions of electron density and differ...

Xinyi Zeng 4C

I wrote "to make sure the law of conservation of mass is obeyed as there should be equal number of atoms of the same element on both sides of the reaction equation", and I got full credit for it. I think the most essential part of the answer is "the law of conservation of mass".

Xinyi Zeng 4C

Is it true that a more electronegative central atom will draw the bond pairs of electrons closer to itself, hence increasing the repulsion between bond pairs and in turn the bond angles(compare NH3 and PH3); while when non-central atoms are more electronegative, bond pairs are drawn further away fro...

Xinyi Zeng 4C

I think it represents the energy required to break the bond, hence denoting bond strength. The more negative the value is, the stronger the bond is.

Xinyi Zeng 4C

It should have both 90 degree and 180 degree

Xinyi Zeng 4C

If you meant triiodide (I3)^-, then it should have a linear structure as there are 3 lone pairs and two bonding pars surround the central I atom.
The Lewis structure will be [I-I-I]^-, with 3 lone pairs surround each I, so the center I will have an expanded octet structure.

Xinyi Zeng 4C

Yes, and just to add on, for anions, if they have a larger electron cloud while the electrons are further away from the nuclear, they are more easily drawn away by a cation of high polarizing power, and they are more easily polarized. It is during the process of polarization that a highly polarizing...

Xinyi Zeng 4C

The greater the electronegativity difference between the two atom, the more polar the bond is. Usually a covalent bond formed between two different atoms will be polar, except for covalent bonds formed between C/S/H/P as they have similar electronegativities. If there is polar bond present in the mo...

Xinyi Zeng 4C

I think hydrogen bond is also a type of dipole-dipole interaction, so it is just a strong dipole-dipole interaction, and it usually occurs between polar molecules, too, as it is defined as "electrostatic forces of attraction between the protonic hydrogen of one molecule with a lone pair on a hi...

Xinyi Zeng 4C

Across a period, nuclear charge increases while the electrons are removed from the same shell (which means that the number of inner shells of electrons remains the same), hence the effective nuclear charge increases. Atomic radius also decreases across a period. Hence, valence electrons are increasi...

Xinyi Zeng 4C

If a metal bonds with a nonmetal is this considered a covalent bond? Usually the bond formed between a metal and a nonmetal is an ionic bond. But it may have a covalent character as the nature of the bond formed between two atoms really depends on the electronegativity between the two atoms that wi...

Xinyi Zeng 4C

Once the first electron is removed, the atom becomes a positive ion. It has an overall positive charge, so removing another electron from it would be much harder than removing an electron from a neutral atom due to the electrostatic attraction between the nucleus and electrons. Does this mean remov...

Xinyi Zeng 4C

I think so! As of my understanding, I think ALL ionic compounds have a degree of covalent character. I don't think pure ionic bonds really exist, as this would require an infinitely large electronegativity difference, and complete charge transfer is unfavorable considering the raising of the electro...

Xinyi Zeng 4C

First, consider E (photon)=hv, for frequency of light, v to be the lowest, E should be the lowest possible, too. Now think about E(photon) - work function = E(excess) = Kinetic energy of the ejected electron If we want E(photon) to be the lowest, we can take the E(excess) to be zero. Then, E (photon...

Xinyi Zeng 4C

Yes! In both situations the electron can be ejected, just to add on, the difference is that the ejected electron will have different kinetic energies. When the energy of the photon is greater than the energy required to remove the electron, kinetic energy of the ejected electron will be larger than ...

Xinyi Zeng 4C

My TA said it would be good to know the rough wavelength range. Visible light wavelength range from 400nm (violet) to 700nm (red) is pretty important. Then remember the wavelength from small to large: x-ray and gamma-ray < UV < visible < IR < microwave/radiowaves. Remember the range for UV (350nm) a...

Xinyi Zeng 4C

They do look similar when you are writing them in the answer! What I do to differentiate them is that, I will put what it represents right in front or next to it whenever I am using it or finding its value, like velocity, v=... or frequency, (curvy v)=... Usually they will not appear in the same que...

Xinyi Zeng 4C

Just some relative information to help understand eV better and why it has such a value: eV is the symbol for the electronvolt and it can also be written as electron-volt and electron volt. It is a unit of energy equal to approximately 1.6×10^-19 joules. By definition, it is the amount of energy gai...

Xinyi Zeng 4C

You can find the specific numerical range on this website, too!
http://labman.phys.utk.edu/phys222core/ ... ctrum.html

Xinyi Zeng 4C

Yes, you can find the test and exam schedule right here: https://lavelle.chem.ucla.edu/wp-conten ... hedule.pdf

Xinyi Zeng 4C

Do you know what the reaction is? Is it combustion? You have to know the reactants and products before you could arrange them.

Xinyi Zeng 4C

Yes, we have to. It is in the syllabus for test one!

Xinyi Zeng 4C

605122791 wrote:Hi is it ok to not bother about significant figures in the beginning of calculations (by writing down more than the required sf.), and only round it to the correct number of sf. in the last equation?

Yes, it should be okay to round off at the last step.

Xinyi Zeng 4C

How do significant figures work when the number is larger for instance if there was a problem that said find how many moles of hydrogen are in 2.00 kg of H. The answer is 1,984.127 but how do we know how many significant figures there are when you need more digits just to get back to 0 than were gi...

Xinyi Zeng 4C

I think it's better to remember all the conversions of all prefixes that are mentioned during the lecture: giga=10^9 mega=10^6 kilo=10^3 deci=10^(-1) centi=10^(-2) milli=10^(-3) micro=10^(-6) nano=10^(-9) pico=10^(-12) And also the SI derived units like volume(m^3) and density(kg m^(-3)) bond length...

Xinyi Zeng 4C

If there are multiple parts to one question, like part (a) and part (b), and when we want to calculate the answer for part (b), we need to use the answer from part (a), do we use the rounded off answer or the more accurate raw answer? Or are they both okay?

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