CHEMISTRY COMMUNITY

Xihui Yin 1I

All spontaneous reactions are irreversible but are all irreversible processes spontaneous?

Xihui Yin 1I

Should H2O be omitted from the rate law if it acts as a solvent? One example would be 15.101, where the solution stated to omit it from the chemical equilibrium: ClO- + H2O <=> HClO + OH-. Since K=[HClO][OH-]/[ClO-], and reverse reaction is k'[HClO][OH-], would the forward reaction be k[ClO-] instea...

Xihui Yin 1I

OH- is an intermediate, so why is it allowed to be included in the rate law?

Xihui Yin 1I

The syllabus does not list it, but just to confirm, will we be tested on it during the final?

Xihui Yin 1I

For a), I don't understand why CH3CHBrCH=CH2 would have a lower Ea when it essentially has a different structure from that of the intermediate, bromine aside. For b), I don't understand the solution at all. Do they mean that lower Ea -> faster reaction -> kinetic control predominate, so a reaction p...

Xihui Yin 1I

I used the method of substitution value of Ea and T into the formula k=Ae^(-Ea/RT). For a, I managed to get the correct answer. For b), I used the same method and substituted T=298 and Ea=75000 for k1 and T=350 and Ea=75000 for k2 and divided k2 over k1. However, my answer was wrong and I can't seem...

Xihui Yin 1I

Nucleophiles have an extra pair of electrons (either lone pair or in a pi bond) and can attack an electrophile (an electron-deficient species, e.g. positively charged or partially positively charged) to form a bond. In a sense this means that something with the capacity to form a bond due to its ext...

Xihui Yin 1I

H2O cannot be an intermediate because it is one of the reactants in the overall reaction. Yes, I know, but overall reaction was not given. Considering how you fomulate the overall reaction based on the steps, how would you then know that H2O is not an intermediate when it is in the second step? For...

Xihui Yin 1I

How do you know H2O is not an intermediate, considering how it is not in the first step of the reaction?

Xihui Yin 1I

Not necessarily. What matters is that that have a pair of electrons that can be used to form a bond with an electron-deficient species. This means they either have lone pairs (H2O, NH3, OH-), a pi bond (ethene) or a partial negative charge.

Xihui Yin 1I

For a first order reaction involving half-lives, will I be penalised for using (1/2)^n=fraction of final concentration/original concentration to find the number of half-lives? I know this does not apply to second order and zero order reactions, but I was wondering if I will be penalised for not usin...

Xihui Yin 1I

I had the same question because in the page in Lavelle's website (https://lavelle.chem.ucla.edu/wp-content/supporting-files/Chem14B/Kinetics_Integrated_Rate_Laws_Examples.pdf) it says "*In the following derivations of the three integrated rate laws, we assume the stoichiometric coefficient &qu...

Xihui Yin 1I

Given that the formulas for the various zero first second order reactions assume that the coefficient of the reactant is 1, for cases where the coefficient is not 1, do you have to adjust the formula by the coefficient accordingly? E.g. a A->bB for a first order reaction. Rate= a •k[A], so different...

Xihui Yin 1I

Alyssa Parry Disc 1H wrote:E naught is standard reduction potential and E is the potential of a reaction

Yes, I know, but the textbook uses E.

Xihui Yin 1I

Hi, James, So, as the problem states, aluminum should react with oxygen in basic solution, which means that water, OH- and oxygen should all be involved in your redox reaction. Whenever the metal will be placed in the basic solution, it will form a hydroxide and therefore this should be one of your...

Xihui Yin 1I

Why is E° used instead of E? How is this reaction different from the textbook example of a ion-selective electrodes since the textbook uses E? Do we use the textbook formula for ion-selective electrodes (E=E'-0.05916*pH)?

Xihui Yin 1I

Shouldn't E increase as [CrCl3] decreases? RT/nF*ln[anode]/[cathode] should become larger as lnQ increases since the reaction would favour the products as concentration in anode is decreased (Le Chatelier)?

Xihui Yin 1I

Why is the E° value used here -0.42V (basic) and not +0.82V (acidic)? Don't the transition metals form ligands which hydrolyse to give acidic solutions?

Xihui Yin 1I

Ammar Amjad 1L wrote:Here is a link to a post that answers your question.

viewtopic.php?f=143&t=11404&p=28252&hilit=

Thank you.

Xihui Yin 1I

Why is SO4 2- not reduced? E°(SO4/H2SO3)>E°(Ni2+/Ni)?

Xihui Yin 1I

For the anode, why is it written in the order Ag(s)|AgBr(s)|Br-(aq)? Is this because Br- is an ion/aqueous so it's written closest to the salt bridge? If solids are written on the outside, why is Ag(s) written before AgBr? Is this because it's written from reactants to products? But if it's written...

Xihui Yin 1I

Adrian Lim 1G wrote:Isn't I2 a solid though?

You need a conducting solid.

Xihui Yin 1I

Nvm, I figured out that ∆G=0 for equilibirum but ∆G° varies for different magnitudes of K.

Xihui Yin 1I

It says that standard ∆G for a system at equilibrium=0, but why for varying values of K, representing a system at equilibrium as well, not equal to ∆G=0 itself? I.e. K>1, ∆G<0 as opposed to ∆G=0.

Xihui Yin 1I

dU=0 for an isothermal expansion or compression of an ideal gas only. This is a direct consequence of U = 3/2 nRT for an ideal gas. Therefore, for ideal gases, no temperature change=no internal energy change. Additionally, it's not really possible to expand/compress liquids or solids in the same wa...

Xihui Yin 1I

Do we assume that ∆U=0 for all isothermal reversible reactions, or do we have the make sure that the question explicitly mentions the gas as ideal?

Xihui Yin 1I

I'm really overthinking this unimportant question but what system is a simple calorimeter? I recall it being a closed system because the cup is covered, but it is at constant pressure and isn't sealed, so shouldn't it be open? I've tried searching past posts but the answers all seem to be a mix of e...

Xihui Yin 1I

Just to confirm, we can use q(rev)/T with the q value derived from an irreversible reaction since entropy is a state property right? I.e. use ∆H from an irreversible reaction to calculate q(rev). Are there any exceptions or stuff I have to take note?

Xihui Yin 1I

The problem states that in box A, there is a monoatomic gas, meaning that there are single atoms of gas. The Cv value for atoms is 3/2R. In box B, there are diatomic molecules that are not vibrationally active, meaning these are linear molecules. For linear molecules, the Cv value is 5/2R. In box C...

Xihui Yin 1I

Can someone explain to me why the C values to calculate Box A, B and C are different?

Xihui Yin 1I

Xihui Yin 1I wrote:So what does elementary particles mean?

I got it, nvm.

Xihui Yin 1I

So what does elementary particles mean?

Xihui Yin 1I

Can someone explain to me the solution? What does elementary particles mean?

Xihui Yin 1I

Recall the third law - entropy in a perfect crystal at 0K is 0. This means that at 0K there is no thermal entropy, hence only entropy remaining is positional residual entropy, which is based off the "randomness" of the positions of the molecules/atoms arranged. For example a non-polar mol...

Xihui Yin 1I

Recall the third law - entropy in a perfect crystal at 0K is 0. This means that at 0K there is no thermal entropy, hence only entropy remaining is positional residual entropy, which is based off the "randomness" of the positions of the molecules/atoms arranged. For example a non-polar mole...

Xihui Yin 1I

The question states that the the pressure changes from 16atm to 4atm. Since ∆H=∆U+P∆V, and ∆H=q only under constant pressure, why are we using enthalpy of combustion to calculate heat change when pressure is not constant?

Xihui Yin 1I

How do we determine if a reaction is reversible or irreversible, or will all related questions explicitly state it?

Xihui Yin 1I

ΔH is the thermodynamic potential of the system, and thus includes work done and ΔU, ΔH=ΔU + PΔV. ΔU is the summation of energies in a system. When work done=0, ΔH=ΔU.

Xihui Yin 1I

In the graphite form, carbon is sp2 bonded to 3 other carbon atoms to form a hexagonal ring. However, each C still has a spare 2p orbital containing an electron. The 2p orbitals overlap to form a delocalised pi bonding system and as such, rings of carbons exist as individual sheets. Dispersion force...

Xihui Yin 1I

I'm assuming molar energy refers to the overall summation of all the individual bond energies for one mole of benzene. In the context of the question, benzene has resonance stability. Individually, the summation of separate C-C and C=C bonds without taking into account benzene resonance would result...

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