CHEMISTRY COMMUNITY

Ying Yan 1F

I don't think there is another way, calculating for delta G_ionization is the same as calculating for delta G^o.

Ying Yan 1F

It usually just depends on the units of the information you were given in the problem. I'm pretty sure you won't be marked wrong if you leave your t in either minutes or seconds (or even hour) as it is the correct number of sec/min/hr. I hope this helped!

Ying Yan 1F

As the previous students, mentioned, it is not necessary to know fractional orders for this course. However, if you are curious, fractionals orders usually occur when products are also taken into consideration when writing the rate law. :)

Ying Yan 1F

Yes, you ignore the temperature, it's just extraneous information.

Ying Yan 1F

In regards to the Arrhenius equation that is: ln(k2/k1)=Ea/R(1/T1- 1/T2) One of the interpretation that the textbook stated was: "When T2 . T1, the right-hand side is positive, so ln(kr2/kr1) is positive, which means that kr2 > kr1. That is, the rate constant increases with temperature." I...

Ying Yan 1F

Usually, when we write out rate laws, we take only the reactants into consideration, i.e. for the reaction H 2 + I 2 <=> 2HI, the rate law= k[H 2 ][I 2 ] However, I know there are times that products are written into the rate law too, with a negative order,so my question is: when do we include produ...

Ying Yan 1F

When a problem is asking for you to solve for the pH or when you are given pH in a cell diagram, that's when you would usually use log instead of ln. Hope this helps!

Ying Yan 1F

You would have to balance the redox half reaction to determine what n is, since n is the number of electrons needed to balance the redox reactions. Hope this helps!

Ying Yan 1F

In homework 6L.9, the question asks us to write balanced half reaction and draw a cell diagram for the redox reaction of acidified solution of potassium permanganate and iron(II) chloride which I deduced as (KMnO 4 +FeCl <=> KCl + FeMnO 4 ). For the half reactions, I got from appendix 2B: Fe 3+ + e-...

Ying Yan 1F

For clarifications, the Standard Hydrogen Electrode's significance is that it is utilized to help calculated the standard potential of other electrodes, correct? Thank you!

Ying Yan 1F

Another way you can find if the reaction is undergoing oxidation or reduction is through just balancing the half reactions. If you see that electrons needs to be added to the reactant side, then that half reaction is being reduced (Gain electron reduction); if you see that electrons needs to be adde...

Ying Yan 1F

Oxygen also has an oxidation # of -1 when it is in peroxide (O₂^2-)

Ying Yan 1F

While I know that knowing how to derive the equation is a great way to understand the equation, is it necessary to know how to derive the rate equations (like Prof. Lavelle did in 2/28 lecture) for the final exam? Thank you!

Ying Yan 1F

Activation energy can also be regarded as the "threshold energy" of a reaction, as it is the amount of energy needed for a reaction to actually occur. Hope that helps!

Ying Yan 1F

The reason that the reaction in part b is endothermic is because energy need to be absorbed into the reaction in order to break the X 2 bond. Therefore, since heat is being added into the reactant side of the reaction, increasing the temperature would then make the equilibrium shift towards the prod...

Ying Yan 1F

Rafsan Rana 1A wrote:for 5G.15 I keep getting -2.7 kj per mol but the answer says -27 kj per mol. Can someone tell me what I'm doing wrong is the answer key wrong.

Yeah! I kept getting -2.7 kj/mol too!

Ying Yan 1F

Usually, if the (standard) cell potential is negative, then the galvanic cell is working reversibly. This is because if E is positive, the forward reaction is favored. Hope this helped!

Ying Yan 1F

You add H 2 O whenever reactants and products in half reaction have different amounts of oxygen atoms in order to balance the reactions out. Then, depending on whether the reaction is in a basic solution or acidic solution, you at H+ or OH- to balance the reaction with the added water molecules out....

Ying Yan 1F

What is the difference between doing a redox reaction for an acidic reaction and a redox reaction for a basic reaction? Thank you!

Ying Yan 1F

A reaction is spontaneous when E is positive and delta G is negative. Hope that helps!

Ying Yan 1F

When calculating standard cell potentials, if I multiply the one of the half equations by 2, do I multiply the corresponding standard cell potential by 2 too? Thank you!

Ying Yan 1F

In equilibrium, the activities constant Q is equivalent to the equilibrium constant K, that is why, when a reaction is at equilibrium, when can state that Q=K and replace Q in the equation delta G= -RTlnQ with K: delta G=-RTlnK. I hope this helps!

Ying Yan 1F

The basic concept of Gibbs free energy is the energy *available* to do work by a system. It also tells us the spontaneity of a reaction, (another work to describe it is if the reaction is thermodynamically favorable). If delta G is negative, that means the reaction is spontaneous, and if delta G is ...

Ying Yan 1F

An isothermal system is one where no heat nor matter is transferred externally, meaning that the energy will always stay the same in the system. That is why U=0 in an isothermal reactions.

Ying Yan 1F

Look at the units of the constant and units of the problem to determine which constant to use! Usually, when doing thermodynamics we will be using 8.314. Hope that helps!

Ying Yan 1F

Exactly! Just like how a room naturally gets messy over time, the entropy( disorder) of the universe is constantly increasing, and work must be put in in order to decrease the entropy of a system.

Ying Yan 1F

From what a recall, Delta H of formation and condensation will usually be given to you in a problem, and you will need to find the net delta H through the given values.

Ying Yan 1F

Since no heat is exchanged with its surrounding, q=0. Thus since -q=w, w will also be 0.

Ying Yan 1F

Enthalpy is vaporization should be addition because bonds are being broken, and energy needed to break bonds. On the other hand, during condensation, intermolecular bonds are being formed, therefore, energy is being released and it is a subtracted. I hope this helps!

Ying Yan 1F

Since single, double, and triple bonds all have different bond enthalpies, I believe the safest way to go about solving bond enthalpy question would be to draw out the lewis structure, so you can see the number of bonds formed between molecules.

Ying Yan 1F

Usually, there are key works in the problems that tells you if a system is reversible or irreversible. For instance, constant pressure means that the system is irreversible and you would use the equation w=-P(delta)V to calculate work. Hope that helps!

Ying Yan 1F

Yes, an insulated water bottle would definately be a isolated system because no heat nor matter can be transfered. On the other hand, a normal water bottle would be an example of a closed system because while matter cannot be transfered, heat still can be transfered.

Ying Yan 1F

No we did not, so far we've only covered w= P(ex) * change in V.

Ying Yan 1F

The equation for calculating internal energy is u= q + w.

Ying Yan 1F

It is probably interchangable because we usually only need the change in temperature, and regardless of whether the temperature is in Kelvin or in Celcius, the amount that changed will still be the same.

Ying Yan 1F

If water is in its gas phase in the reaction, then you do include it in your equilibrium ratio.

Ying Yan 1F

No, you do not because you do not include them in your equilibrium ratio.

Ying Yan 1F

If you have a K value that is smaller than 10^-3, then you can use the approximation shortcut. If you still need more clarification, Dr. Llavell talks about this in Video Module 3. Hope that helped!

Ying Yan 1F

That is correct! The lower the pH, the more acidic a substance is, and the higher the pH, the more basic a substance is.

Ying Yan 1F

We don't included solids and pure liquids when solving for K because they don't have affect the concentration of the other reactants and products and does not exhibit a partial pressure. Hope that helps!

Ying Yan 1F

It really depends what information the problems gives you. If the concentrations of the reactants and products are given, then you you Kc, on the other hand, if the pressure of the reactants and products are given then you use Kp.

Ying Yan 1F

Homework #3 should probably on the Acid and Base Equilibria since that is what llavel is teaching in the past few lectures.

Ying Yan 1F

If you are only given intial concentrations of the reactant and products and the K value, then create an equilibrium ratio and solve for Q. If Q < K, then the reaction is moving in the forwrd direction, and the reactants will have -x while the product is +x. On the other hand, if Q > K, then the rea...

Ying Yan 1F

Inert gases usually won't react with reactants already present in the reaction, therefore, it will not change the concentration of the reactants nor products, and since the concentrations don't change, the equilibrium remains the same.

Ying Yan 1F

I'm redoing the post-assessments and can't quite figure out this problem either! I keep getting K= .25 (but the correct answer is 4.98).

Ying Yan 1F

A large K value indicates that there are more prouducts present in the reaction while a small K value indicates that there are less product (and thus more reactant) present in the reaction.

Ying Yan 1F

Solid and pure liquids cannot really react effectively with other substances and doesn't have a concentratio, therefore they are not included in the equilibrium constant equation.

Ying Yan 1F

As the previous posts stated, Le Chatelier's principle just means that a reaction will adjust in order to go back to equilibrium.

Ying Yan 1F

Le Chatelier's principle means that a reaction will adjust itself to keep its equilibrium (constant K).

Ying Yan 1F

This is sort of a dumb question, but what is the purpose of an equilibrium constant? Why are they useful? Thank you!

Ying Yan 1F

I read from the textbook that terminal atoms are not regarded as hybridized. (i.e. the Cl molecules in PCl₅) What are the definition of terminal atoms? Thank you!

Ying Yan 1F

^Exactly, if I remember correctly, we will only start doing calculations for titrations in 14B or 14BL.

Ying Yan 1F

^Furthermore, because F is so electronegative, the H-F bond is shorter, and make it harder for the H+ ion (aka proton) to dissociate from the HF molecule.

Ying Yan 1F

pH calculates is the amount of H+ in a solution while pOH calculates the amount of OH-. Both utilizes -log to determine their concentration, however, for pOH, you must subtract the value you get from the -log[OH-] to get the correct answer. I hope that helped!

Ying Yan 1F

Yes they are, polyprotic acids/bases are simply bronsted acids/bases that can donate/accept more than one proton.

Ying Yan 1F

Usually, if a molecule has more than one hydrogen molecule, it means it is polyprotic (I.e. H2SO4) since it shows that they are able to donate more than one proton. As for polyprotic bases, they are able to accept more than one protons, therefore, you can look out for those when you see a molecule w...

Ying Yan 1F

Usually, if a molecule has more than one hydrogen molecule, it means it is polyprotic (I.e. H₂SO₄) since it shows that they are able to donate more than one proton. Hope that helps!

Ying Yan 1F

I had that same question when I was doing the homework too! I believe unless specified otherwise, I would do a monoprotic proton transfer. (But technically, you are wrong! The two molecules are polyprotic.)

Ying Yan 1F

805097738 wrote:So bronsted and lewis acids and bases are the same thing just described differently based off of e- or H+ action?

Exactly! Lewis and Bronsted acids/bases are kind of like the inverse of each other. I.e. Lewis acids are electron acceptors, bronsted acids are proton donors.

Ying Yan 1F

Lewis acids are election acceptors, therefore since Ag+ and BF₃ have the ability to accept electron, they are lewis acids. (Whereas electron donors are lewis bases.) Hope that helped!

Ying Yan 1F

In the coordinating compound [Fe(CN)₆]^4-, why is the name Hexacyanoferrate and not

instead Hexacyano"iron-ate"?

Ying Yan 1F

It really depends on how many lone pair the molecule have. If there is only one lone pair, then the angle will be slightly-less-than 120 degrees, if there are two lone pairs, then the angle will be slighty-less-than 109.5 degrees.

Ying Yan 1F

Is it necessary to know how density isourface and electrostatic potential surface works? (They were discussed in the textbook) Thanks!

Ying Yan 1F

Can someone please explain the valance bond theory? Thank you!

Ying Yan 1F

Just for clarification, T-shaped is 3 atoms with 2 lone pair and trigonal pyramidal is 3 atoms with 1 lone pair, correct? Thanks!

Ying Yan 1F

Bent and angular is the same shape :)

Ying Yan 1F

The region of electron density for an pi bond is not actually on the bond axis, but rather parallel "on top" and "below" it, creating a bean-shaped region of e- density. Therefore, if the bond rotates, the bean-shape will break because the regions of electron density are no longe...

Ying Yan 1F

Yes, Dr. Lavell confirmed that hybridization will not be on test two :)

Ying Yan 1F

I was confused about this too, but I later realized that the key way to distinguish between the two is that e- arrangement takes into consider the numbers of lone e- pairs and shared e- paired (aka bonds) to determine the name while VSEPR only take into consideration on the number of atoms around th...

Ying Yan 1F

Someone asked this question in my lecture a few days ago, but I would like to ask about it again: What kind of bond would a resonace bond be classified as? For instance, would a molecule with a double bond resonance consider to have a pi bond or sigma bond? Thanks!

Ying Yan 1F

Is it necessary to remember the names of all the molecular shapes? I know linear, triangular planarm, tetrahedral are very common molecular shapes so it's good to remember them, but what about the other shapes such as trigonal bipyramidal, square pyramidal, etc.? Thank you!

Ying Yan 1F

Kaylee Sepulveda 3C wrote:Usually, the elements that do this are B, Al, Li, and H. B and Al will usually form compounds where they only have six electrons instead of a complete octet.

Why does B and Al exhibit this behaviour (where they don't form a complete octet)?

Ying Yan 1F

For all molecular structures the atoms should have a formal charge where the molecule equal zero or equal to the charged the molecule is assigned. I hope that helps!

Ying Yan 1F

Please correct me if I am wrong, but does VE also stand for potential energy? Thanks!

Ying Yan 1F

^ Dissociation energy is positive because energy is need to break the bond. On the other hand, when bonds are formed, energy is release and that value of energy is negative.

Ying Yan 1F

I am pretty sure we can still do homework in the Chemical Bond section, as long as it is from 2E-2F.

Ying Yan 1F

Electron affinity has a similar trend to ionization energy, where it increases up and to the right. Hope that helps!

Ying Yan 1F

The xyz helps to identify what position the subshell that the electron are located are in. (i.e. 2px the subshell is horizontal, 2py diagonal, and 2pz vertical) Hope that sort of helped!

Ying Yan 1F

When reaching the d block, which is the correct way to the write the electron configuration, 3d 4s or 4s 3d? I've noticed it written both ways, and it made me kind of confused. Thank you!

Ying Yan 1F

When drawing lewis structures, how should I go about determining the central atom? I noticed on a lot of molecules that even though Oxygen has the higher ionization energy, Carbon or Sulfur is the central atom. Thanks!

Ying Yan 1F

How can I distinguish that a molecule is bonded by a coordinate colvalent bond? Thanks!

Ying Yan 1F

The bond length was 1.24 Angstrom because that molecules was exhibits resonance. The 1.24 Angstrom means that the bonds in the NO₃ molecule are hybrid between a double bond and a single bond. Hope that helps!

Ying Yan 1F

I believe an atom's electronegativity is relative to their ionization energy (increases from left to right and down to up of the periodic table) , so I would just follow the trend for ionization energy to determind an atom's electronegativity.

Ying Yan 1F

Just to clarify, the way we distinguish between whether a compund is bonded "covalently" or "ionically" is to see if the atoms in the compound are bonded metals to nonmetal(ionic) or nonmetal to nonmetal (covalent)? Sorry this is such a terribly worded question, I hope you guys c...

Ying Yan 1F

Jorge Ramirez_4H wrote:Is electronegativity important when doing electron configurations?

Not particularly, electronegativity is important for determining the bond that will form between atoms, so for drawing lewis structures but not electron configurations.

Ying Yan 1F

Electronegativity is an atom's ability to hold on to an electron. Therefore, it increases across a period because the ionization energy of an atom also increases across a period, meaning the atom is able to "hold on" to its electron better.

Ying Yan 1F

sbottomley3a wrote:A helpful mnemonic device to remember the order is "I saw my Grandma's X-rated Underpants Visible In My Room" (Gamma, x-ray, uv, visible, infrared, micro, radio). It's a little wacky, but it works!

Haha! This is great! Thanks for the mnemonic device

Ying Yan 1F

I know we've disscussed this topic a a few weeks back, but can someone clarify the idea of black body radiation? Thanks in advance!

Ying Yan 1F

Just from doing some problems, I believe the reason we combined the two equtions is solely dependent on the amount of information given in the problem. For instance, when we are solving for the energy of the photon, we have to combine the equation because we need/ were given wavelenght and thus need...

Ying Yan 1F

cycle .s^-1

Ying Yan 1F

On question 1A.9 I understand that the key equation is C=(wavelength)(frequency), however the question also asks for the energy of photon, how do I calculate for that? Thank you!

Ying Yan 1F

If this helps, I associate black bodies with black holes, where, as the previous comments have already explained it emits and absorbs all frequencies of radation, just like how a black hole absorbs light and both the black holes and the black bodies are invisible. :)

Ying Yan 1F

Ionic bonds are much stronger since electrons from one atom is given to another and the two atoms basically are glued together through the bond. On the other hand, in covalent bonds the atoms are merely 50/50 sharing the electrons, therefore not as strong as an ionic bond.

Ying Yan 1F

Can anyone clarify why circlular standing waves around the nucleus illustrates why electrons have qunatized energy states in atoms? Thank you!

Ying Yan 1F

Yeah I agree with the previous few answers, look at number that has the least amount of significant figures in the problem, but usually it is just four or five sig figs.

Ying Yan 1F

To reaffirm the previous comments, just work out the porblem in the way you are comfortable with. As long as you show how you did it, I'm sure points will be given. :)

Ying Yan 1F

I think I can confidently say yes, since stoichiometric coefficients must be whole numbers.

Ying Yan 1F

Sorry this is reptitive of other posts, and I actually didn't know to do this before myself(!), but the best way to balance a non whole number stoichometric coefficient is to write the coeifficient in improper fractions and multiply both the reactant and product compounds by the denominator of the f...

Ying Yan 1F

Personally, the dilution/molarity problems that confuses me are ones with more than two compounds, and in those cases, the key to solving the problem is to find the ratios of those ions/compouds in relation tto either the other ions/elements.

Ying Yan 1F

From what I remembered, for + and -, you look at the sig figs AFTER the decimal point (i.e. 1.36 + 3.5 = 4.9 [1 sig fig after decimal point]) , while for multiplication and division, you look at the entire numbers to evaluate the sig figs (i.e. 2.51 x 6.111 = 15.3 [3 sig figs]).

Search found 101 matches