CHEMISTRY COMMUNITY

Clement Ng

In chapter 9 #75, the molecule cis-MX2Y4 has a higher molar entropy than trans-MX2Y4.

Clement Ng

2013 exam*

Clement Ng

E = Eo - RT/nF * ln Q
E = Eo -0.05916 V/n * log Q

In the 2016 final exam #4A, I used the latter equation but the answer key used the first equation. I got roughly the same answer (944V). The answer key said 942V. Would I get marked down for an answer a few volts off?

Clement Ng

What are the equations of the definitions for the 3 laws of thermodynamics?

For the 2nd law, is it right to say that 2nd law is deltaS(univ) > 0?

For the 1st law, is it delta U univ =0?

Clement Ng

Do salt bridge/porous disk: does it allow cations to move or do they only allow counter ions such as Cl- to be transferred?

Clement Ng

Why do cis molecules have a higher molar entropy than trans molecules?

Clement Ng

w(max) = deltaG of a voltaic cell, but then the units of w are J and deltaG's units are J/mol. Why is this?

Clement Ng

Whenever a redox equation is acidic or basic, is the H+/OH- ion on the left side of the equation or the right?

Clement Ng

Practice Exam Problem:

How many views does Chemistry Community have? (10 pts)

a) 100,000

b) 1,000,000

c) 5,000,000

d) none of the above

Clement Ng

Is it me or did I stumble into 14C today?

Clement Ng

Is there any good mnemonic device for memorizing all the functional groups?

Clement Ng

The step with the smaller k value.

Clement Ng

No, I wouldn't see a reason why you would be penalized for using that equation. As long as it helps you get the right answer, you're good.

Clement Ng

me: that midterm was so easy

me: *gets back grade

Clement Ng

I think it's because the rate for consumption is negative[change in concentration]/change in time, and the change in concentration was negative. Thus, the answer was positive.

Clement Ng

For those who took the test for 2I, is Q=1?

Clement Ng

How would you rank different reactions' oxidizing power based on their reduction potentials?

Clement Ng

In the solutions manual for #35.b in chapter 14, it uses the half reaction In3+ + 2e- --> In2+, but in the appendix, the half reaction is In3+ + 1e- --> ln 2+. Is this a mistake?

Clement Ng

What's the difference between E and Eo?

Clement Ng

When cell potential is negative since anode potential is larger than cathode, the reaction does not favor products. Can we assume that the reaction favors reactants then? (chapter 14, #31.b)

Clement Ng

In the cell diagram for chapter 14 #29.c, the cell diagram goes Pt(s) l H2(g) l H+ (aq) ll Fe2+, Fe3+ l Pt(s). Does the order of the iron ions within the brackets matter?

Clement Ng

In the back of the textbook, appendix 2, page A18, it says that Fe2+ + e- --> Fe2+. Eo= +0.77V. Isn't the charge of the ion supposed to change?

Clement Ng

When determining the sign of delta S, do you look at only moles of gas on both sides of reaction or can you also look at moles of liquid and solid?

Clement Ng

How are delta S total and delta G related?

Clement Ng

On 9.63, it says that whenever deltaG (formation) is negative, it is thermodynamicaly stable. Why is this?

Clement Ng

Is there a difference between delta S (molar) and delta S (formation).

Clement Ng

A sample of 1 mole of gas initially at 1 atm and 298 K is heated at constant pressure to 350 K, then the gas is compressed isothermally to its initial volume and is then cooled to 298 K at constant volume. Why are deltaS(sys) and deltaG zero in this case? Which equations would you use to figure what...

Clement Ng

Will electrochemistry be on the midterm? If so, up to what part?

Clement Ng

Could someone explain to me how do equilibrium and reversible reactions relevant when answering the question: "Is delta Surrounding = - delta System" ?
This was on Lyndon's practice midterm #3f.

Clement Ng

How is it possible for H20 gas to stay in that form at 25 Celsius?

Clement Ng

What is deltaH when chem community is on fire?

Clement Ng

deltaS= q(rev)/T. Will we ever use q(irrev)to calculate deltaS and if so when?

Clement Ng

Usually when temperature is constant and no chemical reaction is occurring.

Clement Ng

I understand that at constant pressure, q= delta H, but do you use enthalpy of the reaction or enthalpy of formation?

Clement Ng

In an isothermal system, if the change in moles is not zero, would delta U still be zero?

Clement Ng

Why is it that at constant pressure C= delta H/ delta T but at constant volume C = delta U/ delta T?

Clement Ng

Could someone explain this problem to me? A constant-volume calorimeter was calibrated by carrying out a reaction known to release 3.50 kJ of heat in 0.200 L of solution in the calorimeter (q 3.50 kJ), resulting in a temperature rise of 7.32 C. In a subsequent experiment, 100.0 mL of 0.200 m HBr(a...

Clement Ng

Conceptually what's the difference between reversible and irreversible processes?

Clement Ng

Conceptually what's the difference between reversible and irreversible processes?

Clement Ng

Questions about both reversible and irreversible have been on the homework, so it's safe to assume that they may be on the test.

Clement Ng

Yep! P is pressure too.

Clement Ng

When calculating work, when do you multiple -PdeltaV by 101.325 J/(atm*L) versus multiplying by (8.314 J*K*mol-1)/(0.08206L*atm*K-1*mol-1)?

Clement Ng

Yes there's a sign change, because the reaction would change from endo to exothermic or vice versa.

Clement Ng

Sublimation is the phase change from solid to gas, and vaporization is the phase change from liquid to gas and fusion is the phase change from slid to liquid.

Clement Ng

Yeah it's 3 times.

Clement Ng

Einstein constant is a cosmological constant that Einstein used to describe general relativity. It is not the inverse of the planck's constant.

Clement Ng

No, it is not. HClO4 and HCl are strong acids.

Clement Ng

myoglobin and Fe. It is used to transport O2 molecules

Clement Ng

my gpa

Clement Ng

Why is the electron configuration for Cl -2 [Ne] 3s^2 3p^6 4s^1 and not [Ar]4s^1?

Clement Ng

Is any knowledge of titration required on the final?

Clement Ng

Do we have to know how to name acids and bases?

Clement Ng

It's probably a typo. I think it meant concentration.

Clement Ng

pH is equal to 14-pOH. pH can be calculated from concentration of H3O+ and pOH is calculated from concentration of OH-.

Clement Ng

What was the combustion reaction for the skirball fire?

Clement Ng

Let's say there is a chemical equation that involves a gas and an aqueous solution. If the questions asks for K, do you include only gas, only concentration, or both?

Clement Ng

How do you know the number of bonds a central metal atom has in a coordination compound?

Clement Ng

The hybridization of a sulfate ion would be sp3. You can picture it like it's Ch4 as if it's a tetrahedral. Hope this answered your question.

Clement Ng

You would determine the charge on coordination compounds by comparing the charges of the ligands, which are given in a table on professor Lavelle's website. The charge of the metal/central atom can be given by the name of the compound. (ex: (IV)) By combining all the charges of the central atom and ...

Clement Ng

The molecule may have an electron configuration of a square planar.

Clement Ng

It is also important for the production of red blood cells and myelin sheath.

Clement Ng

Can someone explain the structure of hemoglobins and how they bind and disconnect oxygenatoms?

Clement Ng

You can think of sigma bonds connecting atoms directly along the x-axis while pi bonds connect the two atoms between the top and bottom of the y-axis of atoms.

Clement Ng

S+ usually refers to the atom which lost an electron while S- refers to the atom that gained an electron.

Clement Ng

What is the definition of electron density?

Clement Ng

You draw a resonance structure by drawing all the possible structures and arrows that show that the molecule oscillate between the different lewis diagrams.

Clement Ng

S blocks are written before d blocks always, unless the n value of s is equal or higher than the n value of d.

Clement Ng

The equation in the book uses the formula: frequency = R(1/n^2 - 1/N^2)

However, when I google the formula, it is 1/wavelength = R(1/n^2 - 1/N^2).

Why is that?

Clement Ng

This is because in the formula v= R(1/n^2 - 1/N^2), if n was 3 and N was 1, the frequency would be a negative number.

1/9 - 1/1 = negative number.

Clement Ng

Non metals are not likely to exhibit any photoelectric effect, because only metals have 'spare' electrons available in their outer shells.

Clement Ng

The answer is threshold energy.

Clement Ng

For multiplication and division, the least number of significant figures in any number of the problem determines the number of significant figures in the answer. For example 4.00 x 3.0 = 12 Since the number with the least sig figs in the problem is "3.0", which has 2 sig figs, the answer h...

Clement Ng

Yes, that is correct. To answer this question in simpler terms, you take the excess moles of oxygen left over from the first reaction, and use that value to calculate the number of moles of P4O10 formed. Then, you use the moles of P4O6 formed from the first reaction to find the moles of P4O10 formed...

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