CHEMISTRY COMMUNITY

Helen Shi 1J

Is delta U zero for all reversible reactions or just isothermal?

Helen Shi 1J

Can we only find the concentration of reactants with integrated rate laws, or is the reverse law applicable to the concentration of products?

Helen Shi 1J

Can we only find the concentration of reactants with integrated rate laws, or is the reverse law applicable to the concentration of products?

Helen Shi 1J

Because the rate is constant, you can assume that this rate is zero order, which mean that the rate will just equal the reaction constant. Since the rate is in units of M/s, you can set the rate equal to an amount of change in the molarity over a time interval. Then you can plug in the change in mo...

Helen Shi 1J

What is the difference between the rate law and the integrated rate law?

Helen Shi 1J

The rate of C2 gas consumption in this reaction is constant throughout and is given as 0.250 M/s. If you reaction vessel starts with 0.35M of ABC, how long will it take to get to 24.00M of ABC? The equation give is AB+C-->ABC. Can someone explain how they did this please. You basically balance the ...

Helen Shi 1J

So if given a chemical equation, does the coefficient in front of the reactant automatically translate into the exponent in the rate law? So 2NO as a reactant would have a rate law = k[NO]^2?

Helen Shi 1J

The rate of A2 gas consumption in this reaction is constant throughout and is given as .550 M/s. If your reaction vesset starts witih .45 M of AC how long will it tkae to get to 36.00M of AC?

A2+BC = AC + B2

How do you do this question?

Helen Shi 1J

Can someone explain what exactly is the rate constant?

Helen Shi 1J

How do you solve question 61?

Helen Shi 1J

Can someone explain 5.13 and how to get the initial reaction rate?

Helen Shi 1J

So what is the unique rate of reaction for Hw 15.3 part c? There is no answer in the textbook.

Helen Shi 1J

How come the textbook answer for 15.3 part a) is 6.5 x 10^-3 mol/L*s? Why did they not divide by the number of moles (2)?

Helen Shi 1J

Can someone explain part b and c too?

Helen Shi 1J

When would you use the equation with E=E-RT/NF lnQ vs E=E-.05916V/N logQ?

Helen Shi 1J

If CU2+/Cu is .34 volts then wouldn't the reverse reaction where copper loses electrons be -.34?

Helen Shi 1J

Can someone explain how do part d, especially writing the half redox reaction for the left side? How did we know H2O was the reactant for the left but O2 the reactant for the right?

Helen Shi 1J

Curtis Wong 2D wrote:So the order is typically Inert Metal (if applicable) | (Anode reactant) | (anode product) || (Cathode reactant) | (cathode product)| (Inert Metal if applicable).

Then how come for problem 14.11 the cathode reactant and the cathode product is switched so that Cl- is before Cl2?

Helen Shi 1J

How come in the textbook pg 575 when the order of the galvanic cell | (Anode reactant) | (anode product) || (Cathode reactant) | (cathode product)| is flipped so that the cathode is on the left the voltage is negative, even when the electrons are still flowing from anode to cathode?

Helen Shi 1J

What is voltage? Why do we need to multiply voltage with mols x Faraday's constant to get G?

Helen Shi 1J

What exactly is an electrode?

Helen Shi 1J

So the complexity of the molecule overrules positional disorder?

Helen Shi 1J

How do you solve for 11.19?

Helen Shi 1J

Why is it that in a free expansion (according to page 346 in the textbook) that delta S of the surroundings is equal to 0 but delta S (system) is not. The book reasons that no work is done in free expansion so q=0, but if that is the case how can delta S (system) or delta S (total) be anything other...

Helen Shi 1J

Why is it that in a reversible expansion delta U is equal to zero?

Helen Shi 1J

I understand that the units for entropy is J/K, but can someone explain the reasoning behind it other than that it comes from the equation: delta S= q/T?

Helen Shi 1J

I don't understand why the delta S of the surroundings is zero in an irreversible process. The textbook on page 346 says that no work is done in free expansion so w=0. Can someone explain that?

Helen Shi 1J

Can someone explain how to do 9.43?

Helen Shi 1J

you use Avogadro's number because we want to find the amount of entropy per mol, so we need to take into account all the atoms within one mol.

Helen Shi 1J

In what cases is delta U=0? Why is delta U zero in an isothermal expansion?

Helen Shi 1J

Another way to think of entropy is the a state of relaxed disorder. Since Gibbs free energy is the amount of energy free do do work and the change in Gibbs is the energy that was needed to do work (or make a reaction happen) it is affected by the amt of heat or energy coming and leaving the system (...

Helen Shi 1J

Can someone explain why we divide q by temperature?

Helen Shi 1J

Can someone explain how you solve number 9.5? Like what do you divide the heat with?

Helen Shi 1J

Since using Kelvin or Celcius will give different answers, which one should we use?

Helen Shi 1J

So what is the system and surroundings in a calorimeter with constant pressure and a bomb calorimeter?

Helen Shi 1J

H is simply enthalpy whereas delta H is the change in enthalpy. Enthalpy itself is the total heat content (energy) of a system: aka the internal energy plus the product of pressure and volume. My guess as to why we use the change in enthalpy is because it is easier to calculate through experiments.

Helen Shi 1J

However, when bonds are broken isn't energy released as well? So why is it not exothermic?

Helen Shi 1J

Could you also add up all the bond enthalpies for all bonds of the products minus all the bond enthalpies for the reactants to find the reaction enthalpy?

Helen Shi 1J

I am a little confused about how systems under constant volume differ from those under constant pressure. For systems under constant volume, how is pressure changing and how do we find the work enacted on the system?

Helen Shi 1J

If the system expands or is compressed is there still a change in the net number of moles? If not, would the equation P∆V=∆nRT still hold true because the net number of moles aren't changing?

Helen Shi 1J

Can someone explain why the thermochemical equation on pg 288 example 8.7 is that change in enthaply= q x (2 mol)/n? Why would you divide the stoichiometric coefficient of original equation by the number of mols?

Helen Shi 1J

Is there a change in work in the form of volume or pressure? isn't the reaction already contains a mol of OF2? How do you calculate the change in work if so.

Helen Shi 1J

When it asks for the enthalpy of vaporization is it always have to be in mols? or can it be in KJ/g as well.

Helen Shi 1J

what does it mean for heat to be released at a constant volume? Can someone explain why it corresponds to a new heat capacity (C)

Helen Shi 1J

When the textbook refers to the internal energy in example 8.4 on pg 271, is it refering to the heating device or the calorimeter? If it is the calorimeter, wouldn't the change in the internal energy be positive?

Helen Shi 1J

I don't really get why you need to add the heat of the kettle and the heat of the water together. I thought it was just asking for the heat supplied to the kettle to heat it up to 100 degrees Celsius.

Helen Shi 1J

Can someone explain exercise 8.1 part e? Why would mercury in a thermometer be a closed system rather than isolated?

Helen Shi 1J

Lavelle's office hours conflict with my LS30B math class. Is there any other way I can meet up with him to ask questions or is the only other option the TA office hours?

Helen Shi 1J

Acetic acid is used as a solvent for some reactions between acids and bases. (a) Nitrous acid and carbonic acids are both weak acids in water. Will either of them act as a strong acid in acetic acid? Explain your answer. (b) Will ammonia act as a strong or weak base in acetic acid? Explain your answ...

Helen Shi 1J

Why does this answer differ from the table 12.1 acidity constants? Shouldn't the Ka of HClO2 be the same?

Helen Shi 1J

Can someone explain why BaO is basic and As2O3 and Bi2O3 amphoteric?

Helen Shi 1J

Wouldn't increasing the frequency of a light even if it originally did not have the energy to emit an electron eventually lead to an electron being emitted from the metal, because if E=hv and v increases, wouldn't the energy of the photon increase until it surpasses the work function?

Helen Shi 1J

What makes a strong acid completely ionize or disassociate as opposed to a weak one?

Helen Shi 1J

What is the oxidation number?

Helen Shi 1J

A 0.10-mol sample of pure ozone, O3, is placed in a sealed 1.0-L container and the reaction 2 O3(g)∆3 O2(g) is allowed to reach equilibrium. A 0.50-mol sample of pure ozone is placed in a second 1.0-L container at the same temperature and allowed to reach equilibrium. Without doing any calculations,...

Helen Shi 1J

Why in equilibrium the reaction of reactants turning into products and vice versa is still happening? Why doesn't the reactants completely react with each (so their concentration reaches zero) to form the product?

Helen Shi 1J

can someone explain part c in detail, please?

Helen Shi 1J

Can someone explain what does the numbers in front of the hybrid orbitals mean? Like 2(sp2) or 1S. Is it the number of hybrid orbitals there are or is it related to the row on the periodic table?

Helen Shi 1J

An organic compound distilled from wood was found to have a molar mass of 32.04 g·mol"1 and the following composition by mass: 37.5% C, 12.6% H, and 49.9% O. (a)Write the Lewis structure of the compound and determine the bond angles about the carbon and oxygen atoms. (b) Give the hybridization ...

Helen Shi 1J

Is there any way to re-grade the midterm, because I checked the solutions for midterm and for Q8B I feel like I should get partial credit for saying that the compound was a radical even if Lewis structure might be slightly off. Also how many points should be taken off with we make one mistake, like ...

Helen Shi 1J

Can someone explain what dipole is?

Helen Shi 1J

Why do we not count the lone pairs on other atoms bonded to the central atom as regions of electron density?

Helen Shi 1J

Do we only count the lone pairs on the central atom as regions of electron density?

Helen Shi 1J

Can someone explain what a radical is?

Helen Shi 1J

Why is the element with the lowest ionizing energy is in the center?

Helen Shi 1J

Can someone explain specifically how you get the chemical formula for part (c) aluminum hydride and (e)bismuth(III)fluoride?

Helen Shi 1J

It is because the orbitals of Carbon is only 1/3 filled whereas Nitrogen has 3 out of the 6 electrons which is more balanced, thus it does not require another electron as much.

Helen Shi 1J

Why is energy released when electrons is added to a gas phase atom?

Helen Shi 1J

Can someone explain to me why the answer to part (c) is (n-1)d^5ns^2 rather than (n-1)d^3ns^2?

Helen Shi 1J

If both structures have the same net charge then why is one "better" than the other?

Helen Shi 1J

What is the effective nuclear charge?

Helen Shi 1J

Can someone explain how electron shielding works?

Helen Shi 1J

How can an atom have the same properties when they lose an electron if different elements are separated with just a one-electron one proton difference.

Helen Shi 1J

How does the amplitude of the waves correspond with the lower frequency?

Helen Shi 1J

How did you get 2.5x10^-19 as the work energy?

Helen Shi 1J

Can someone explain part a) Calculate the mass, in grams, of one water molecule?

Helen Shi 1J

Can someone explain part a) Calculate the mass, in grams, of one water molecule?

Helen Shi 1J

For part b) First, find the number of moles for just K2S because that is the only molecule that has sulfide: .500 grams/(39.1(2) +32.06) = .00453 moles Then multiply .00453 by ratio of moles of sulfide over K2S, which is 1/1 so you get. Then plug the numbers into the formula: moles/volume= molarity;...

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