CHEMISTRY COMMUNITY

Emma Li 2C

For question 5 in test 2, I'm still confused about what oxidation power means. If the standard cell potential of a reduction half reaction is very positive (ex: F2 + 2e --- 2F- E=+2.87), the book says that the oxidized form is strongly oxidizing. Does that mean that on the test when it gave us the r...

Emma Li 2C

In collisions, what is the frequency factor A?

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Emma Li 2C

In a multi-step reaction, how can you tell which of the reactants and products that cancel out are catalysts instead of intermediates?

Emma Li 2C

Could you explain your thought process for 3b, involving comparing the energy efficiencies of the pots?
I thought that aluminum pots would be more energy efficient because their heat capacity values are the smallest!

Thank you!

Emma Li 2C

I think it's because a constant external pressure is characteristic of an irreversible process, and the pressures of the system vs surroundings being at equilibrium is characteristic of a reversible process.

Emma Li 2C

I was a little confused too seeing that in the table, but I just thought it meant that the book didn't use the half life equation for a second order reaction in one of their examples, or that they just didn't derive the equation for it like they did for the half life of a first order reaction.

Emma Li 2C

we usually don't have to know the derivations!

Emma Li 2C

Hmm is exercise 15.15 a first-order reaction?

Emma Li 2C

Why is the half-life of reactant in a first order reaction independent of initial concentration?

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Emma Li 2C

I think the second one is described as the unique instantaneous rate of a reaction, and the first one as the rate law but they should calculate the same thing!

Emma Li 2C

Is it always only the reactant concentrations that affect the rate law?

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Emma Li 2C

For exercise 15.3 and 15.5, why isn't the rate of reaction of NO2 and the rate of oxygen consumption negative?

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Emma Li 2C

Does constant pressure only apply to irreversible reactions?

Emma Li 2C

Sorry! Is there also a name for the cell that uses the electron current to drive a non-spontaneous reaction?

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Emma Li 2C

What's the difference between a galvanic and voltaic cell?

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Emma Li 2C

For the Gibbs free energy equation, Delta G=delta H-T(delta S), does the change in entropy refer to the entropy of the system, the surroundings, or the total entropy?

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Emma Li 2C

I think doing work means there has to be an opposing force, so a system can't do work in a vaccuum :)

Emma Li 2C

Why is delta U=0 for the isothermal expansion of an ideal gas? (pg 323)

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Emma Li 2C

For hw question 9.31, Iodine vapor has a higher standard molar entropy than bromine vapor at 298 K. Why does Iodine having a larger mass make it have a larger molar entropy?

Emma Li 2C

Both affect! Spontaneity depends on whether or not delta G is negative, so I think any combination of positive/negative enthalpy and positive/negative entropy (except when enthalpy is positive and entropy is negative) can produce a spontaneous reaction if it makes delta G negative.

Emma Li 2C

I think the reaction can proceed spontaneously even when delta H is positive, so maybe it just refers to free energy?

Emma Li 2C

I think another way to say it is when the equilibrium constant equals 1!

Emma Li 2C

What's the difference between the equation for change in entropy and the equation for heat capacity?

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Emma Li 2C

DamianW wrote:In this problem do you have to account for fusion as well ?

Yes! Since there is a difference in temperature between the ice cube and the water, the ice cube would first melt (enthapy of fusion) and then have a temperature change.

Emma Li 2C

A reversible process means that the system is at equilibrium, where the pressure of the surroundings and the system are equal. In expansion, a tiny decrease in the surrounding pressure results in a tiny push up by the system on the piston. If expansion continues to occur in very very small steps, we...

Emma Li 2C

In the heating curve, why is it that the steeper the slope, the lower the heat capacity?

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Emma Li 2C

I was wondering about this as well!
I think that since Professor Lavelle hasn't covered these topics yet in class we should be ok for the exam.

Emma Li 2C

For the enthalpy equation: H = U + PV, if change in enthalpy measures the change in heat without work, why is PV added to the internal energy U?

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Emma Li 2C

Could you explain why gas has two values for molar heat capacity?

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Emma Li 2C

Energy is required to break a bond! Like in an endothermic reaction, energy is inputed and so the energy required to break the bonds is positive

Emma Li 2C

Does it matter if our answer is in J or KJ for this section?

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Emma Li 2C

Why is BF3 considered a Lewis acid?

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Emma Li 2C

For the example Lavelle gave during the lecture, Why is trichloroacetic acid (CCl3OOH, pKa=0.52) a stronger acid than acetic acid (CH3COOH, pKa=4.75)?

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Emma Li 2C

It could focus on what we learned most recently: acids, bases, salts, chemical equilibrium. And I think that Lewis structures might be another big part since we needed to know how to draw them to answer questions in many of the more recent chapters!

Emma Li 2C

What are the angles for a seewsaw molecular shape?

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Emma Li 2C

In a chemical reaction, are we supposed to define the states of the molecules at room temperature or at their state during the reaction? (Ex: H20 is liquid at room temperature but gas after combustion)

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Emma Li 2C

Why aren't solids included in calculating for the chemical equilibrium constant?

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Emma Li 2C

How do you tell if a molecule (with 4 atoms) has a trigonal planar shape or is t-shaped?

Emma Li 2C

I'm a little confused about the difference between shape and electron arrangement. I know that the shape of the molecule only depends on the bonds/locations of the atoms, and the electron arrangement accounts for lone pairs, but I'm confused about why both types of models are needed.

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Emma Li 2C

I think it has to do with Cu being the exception in filling the electron d-block subshells! Because Cu has 10 electrons in the 3d subshell and only 1 electron in the 4s subshell, it would become more stable completing the lone pair in 4s.

Emma Li 2C

How do you tell when to use double bonds and when to just use lone pairs?
NO3- (nitrate ion) has a double bond between N and O, but NF3 has all single bonds and one lone pair.

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Emma Li 2C

Is it recommended to take Chem 14B and 14BL in the same quarter?

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Emma Li 2C

Do orbitals on the same energy level or in the same shell (ex; n=3) all have equal amounts of energy?

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Emma Li 2C

Why do metals have lower ionization energy?

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Emma Li 2C

For elements with 3d and 4s electrons, should the valence electrons include the 3d block as well as the 4s block?
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Emma Li 2C

For the E=-hR/n^2 method!
I kept getting a decimal number too until I tried making the change in energy (calculated from the given wavelength) negative.

Emma Li 2C

Is 1 Angstrom referring to the radius or diameter of an atom?

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Emma Li 2C

I think someone else named them! The book says that Einstein "proposed that electromagnetic radiation consists of particles, which were later called photons."

Emma Li 2C

For the photoelectric experiment, what is actually happening when light "knocks" electrons off of the metal? I thought that it meant electrons are excited to a higher energy state by photons of a high frequency; however, after reading that electrons can only move to other energy levels wit...

Emma Li 2C

How would you know which elements exist as diatomic molecules naturally? (Ex: H2, O2)

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Emma Li 2C

I know combustion reactions require oxygen, but I was just wondering if combustion only occurs if the reactant has both carbon and hydrogen?
Is this reaction in L.7 combustion?
2 C57H110O6 + 163 O2 ->114 CO2 + 110 H2O

Thank you!

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