CHEMISTRY COMMUNITY

Emily Glaser 1F

On formula sheet, I am given that deltaH_vap = 40.7kj/mol

But when I find that using the numbers given, in his equation:
H20(l) --> H20(g)
the deltaH_rxn = 44.01 kj/mol

Why are they different?

Emily Glaser 1F

does delta g = 0 mean equilibrium?

Emily Glaser 1F

Why should the value of delta G be zero at 100 Celsius for water? CONCEPTUALLY. I am referencing 9.91. I get how experimental data can skew numbers, but why should delta G be zero in the first place. Is this saying a phase change is at equilibrium?

Emily Glaser 1F

Why wouldn' you subtract the entropy of vaporization in this problem for part a?

H2(g) + 1/2O2(g) --> H2O(l)
Delta S = Sproducts - S reactants
There is a phase change. We did something like this for enthalpy, so why not for entropy.

Emily Glaser 1F

Why wouldn' you subtract the entropy of vaporization in this problem for part a?

H₂(g) + 1/2O₂(g) --> H₂O(l)
Delta S = Sproducts - S reactants
There is a phase change. We did something like this for enthalpy, so why not for entropy.

Emily Glaser 1F

What does cell potential mean? What does it mean when I have to choose something with the highest reducing power?

When I am doing a galvanic cell, I want to choose the reaction with the cell potential that is more positive? Does more positive mean less reducing power?

Emily Glaser 1F

What's the rule behind writing a cell diagram equation when I have H+ or OH- present in my overall redox reaction? Do I include H+/OH-? How do I include them?

Emily Glaser 1F

In Example 8.6 in the in-chapter problems, I don't understand their reasoning for using C_v in the constant pressure problem.

Why does delta U = nC_vdeltaT for the delta U of a reaction at constant pressure?

Emily Glaser 1F

If q=mCT

and delta S = q/T, doesn't that involve mass (intensive)

Emily Glaser 1F

How do I know what to make the approximation to?

In my slow reaction, I have:

Fast 1st step:
forward O3 rate decomp= k1[O3]
reaverse form rate= kprime1[O2][O]

Slow 2nd Step:
forward O3 consume rate = k2[O][O3]

Why is it k2[O][O3] << kprime1[O2][O]

and not

k2[O][O3] << k1[O3]

Emily Glaser 1F

For finding the rate of formation of NO2 from 2NO(g) + O2(g) --> 2NO(g), Rate of Formation of NO2 = k[NO] 2 [O2] Why do you find reverse of Step 1 but not Step 2. I am aware that Step 2 is a slow reaction and therefore would not affect rate, but the book included it in net rate of formation. You wil...

Emily Glaser 1F

Why don't we divide the average rate by the number of moles.

In this problem, when I found reaction rate of NO₂, I got 0.0065 mole/Ls

Why wouldn't I divide or multiply that number by 2 based off the equation given of 2NO₂ --> 2NO + O₂?

Emily Glaser 1F

Let's say you were given a table of concentrations (reactants and products) at some point in a reaction. When product is produced, it inhibits the reactionn. The equation is A + B --> C A & B are each first order, and C is negative one order. Would the rate law be: Rate=k[A] 1 [B] 1 [C] -1 Is th...

Emily Glaser 1F

So, this is a theorhetically application and not really applicable to real life reactions of multiple reactions in terms of integrated rate laws?

Emily Glaser 1F

What does the rate law mean?

Rate=k[A]

It is just dependent on the concencration of [A]? Not time?

Emily Glaser 1F

Whta if the creation of products inhibits the rate of the forward reaction? How would this be expressed in the rate law equation

Emily Glaser 1F

Can someone explain the conceptual meaning and purpose behind a pseudo reaction

Emily Glaser 1F

You can find the internal pressure of the system using the constants you were given. I did that on the test, and I found that the internal pressure of was not the same as the external pressure

Emily Glaser 1F

Why do I only include reactants in my rate law

rate=k[Reactants]

How would I express it in terms of products?

Emily Glaser 1F

What is the difference between k0 and k1?

Why is k0 for zero order, but k1 for first, second, third, etc order???? Why not k2 for second order?

Emily Glaser 1F

In 14.47, the question provides the cell diagram notation: Pt(s) / Sn4+(aq), Sn2+(aq) // Pb4+(aq), Pb2+(aq) / C(gr) Shouldn't it be reactants / products? Because when I went to do the problem, the manual (and I) did the half reactions and the anode was: Sn2+ --> Sn4+ + 2e- Shouldn't it be written Sn...

Emily Glaser 1F

How should I go about writing the notation for a cell diagram. Can someone break it down for me because some of the things I see in solution manual confuses me

Emily Glaser 1F

What does it mean conceptually when it says "A negatively charged electrolyte flows from the cathode to the anode," which completes the circuit. Is this the salt bridge?

Emily Glaser 1F

If you multiply an equation by a coefficient in order to perform "Hess' Law" on it, you do not multiple the cell potential by the coefficient as you would enthalpy/entropy

Emily Glaser 1F

What exactly is the cathode with cell potential +0.92V in this reaction, 2Hg2+ + 2Br- --> Hg2 2+ + Br2?
Explain

Emily Glaser 1F

I am having trouble understanding how to write a cell diagram notation. In part b, the answer is Pt/O2/OH-//H+/O2/Pt from the equation H+ + OH- --> H2O

How do I know what element/part of equation goes where in the cell diagram notation

Emily Glaser 1F

can someone do step by step of part d. I don't understand why, in the solutions manual, it says:

O2 +2H2O + 4e- --> 4OH- for the cathode (positive E value). OH- is listed before O2, so shouldn't the O2 be on the right side and OH on the left with a positive E value

Emily Glaser 1F

When calculating the n (moles) value in the gibbs free energy equation using cell potential, how do I get that.

How does one get 2 moles from the equation:

2Ce4+ + 3I- --> 2Ce3+ + I3

Emily Glaser 1F

For the reduction reaction of P4 --> 4PH3

Why do I not add an H2O on right side (the side that is reduced state) just like it did in all the previous problems

Emily Glaser 1F

How is O3 --> O2 being reduced, according to this question?

If the oxidation charge on the left is -6 and it is going to -4, isn't that oxidation? Am I doing this wrong?

Emily Glaser 1F

How am I supposed to know that in Cr2O7 2-, Cr has a +6 charge? How would I go about figuring it out?

Emily Glaser 1F

p delta V?

Emily Glaser 1F

pv=nrt

Emily Glaser 1F

Q is when the concentrations/partial pressures change in a system. You use Q to compare to K to see which way the reaction shifts

Emily Glaser 1F

Te questions asks to examine whether compounds are stable with respect to decomp. Th delta G of formation of PCl5 is a negative number (-305kJ), therefore stable. HOWEVER, I am confused because it says with respect to decomposition (PCl5 ---> products) So wouldn't the gibbs free energy be delta G = ...

Emily Glaser 1F

In an isothermal, irreversible free expansion for this question, how do we maintain the temperature if there is no heat input or work despite a volume change since delta S surr = 0?

Emily Glaser 1F

If the q of a reaction is negative, does that mean that the temperature is decreasing.

If delta U is negative, does that indicate a temperature decrease

Emily Glaser 1F

Is something at equilibrium considered reversible? Is is only reversible if at equilibrium?

Emily Glaser 1F

Is

delta U=0
q=0
w=0
delta H=0

in a free expansion?

Can free expansion only occur in an isolated system? Are they synonymous?

Emily Glaser 1F

Is

delta U=0
q=0
w=0
delta H=0

in an isolated system?

Emily Glaser 1F

Are the values of Free Expansion the same as the values for an Isolated System in terms of deltaU, w, q, and deltaH?

All would be equal to zero?

Are free expansion and isolated system synonymous?

Emily Glaser 1F

Closed System with Constant Volume.
Always True, Always False, or True Under Certain Circumstances:

1. delta u=0
2. w=0
3. w<0
4. delta U=q
5. delta U=w

I am confused on this and do not know the answers

Emily Glaser 1F

I know that at constant pressure, delta h = qp.

If not at constant pressure then what does delta H equal?

If w=-PdeltaV, would a changing pressure make it w=-deltaPV?

Emily Glaser 1F

How does delta P come into play in all of this (whether at constant volume or delta V)? How will the equations/values change for delta H, delta U, q, and w?

Emily Glaser 1F

Sorry I mean CHANGING PRESSURE

Emily Glaser 1F

Can someone help me understand what delta H and delta U will be like when PRESSURE is constant in terms of their formulas? What about work and heat?

Emily Glaser 1F

Based on 2nd law of thermodynamics,

Is delta S total of universe = 0?

Or is it constantly increasing? Delta S total of universe = - limit to infinity?

Emily Glaser 1F

Are all reversible reactions at equilibrium since delta S total=0

Emily Glaser 1F

Why is there little change to the reaction when I add water to this reaction.

Wouldn't increasing the amount of water cause favoring of the forward reaction?

Emily Glaser 1F

Let's say we have H2(g) in some larger equation and we are attempting to determine the delta G for this rxn. Exluding the other products and reactants, I want to look at just changes in the values associated with H2. Would the standard molar entropy be 0 (or 130.6 as I found in the Appendix) Would d...

Emily Glaser 1F

Let's say we have H2(g) in some larger equation and we are attempting to determine the delta G for this rxn. Exluding the other products and reactants, I want to look at just changes in the values associated with H2. Would the standard enthalpy of formation be zero? Would the standard molar entropy ...

Emily Glaser 1F

Can/does delta S total=0 when delta G=0? Explain

Does delta G=0 mean its reversible?

Emily Glaser 1F

Why does deltaS total = 0 in a reversible reaction?

Emily Glaser 1F

What's the difference between residual and positional entropy?

Emily Glaser 1F

Why does it make sense that I can calculate the entropy of vaporization of water at 25 degrees Celsius (there is a problem in the book that deals with 85 degrees celcius)? Would I be asked to find the enthalpy of vaporization of water at 25 degrees? And the answer would be different than water's del...

Emily Glaser 1F

Under what conditions does delta Ssys = -delta Ssurr?

In other words, when does delta Stotal = 0

Emily Glaser 1F

When delta G=0, does that mean delta H and delta S are both zero too? Or they have numerical values that cancel?

Emily Glaser 1F

ln(K) = 184.42

To isolate K, use e as a base as according to log rules. e will cancel out the natural log.

e^ln(K) = e^184.42

K=1.2 x 10^80

Emily Glaser 1F

In what circumstance will delta G be zero?

When will delta S be zero?

(Please do not speak in terms of the values of enthalpy and entropy. I want a conceptual explanation, not a numerical one)

Emily Glaser 1F

What was stated in class about H2(g) --> H2(g) and its delta G of formation/entropy?

I know for this reaction, delta H of formation would be zero.
Is delta G of formation zero?
Does that mean delta S is zero too?

Emily Glaser 1F

does polarity of a molecule have anything to do with bond enthalpy?

Emily Glaser 1F

The second law states that disorder is always increasing, thus if I have a reaction with decreasing entropy, then the surroundings would have increases entropy. How would I calculate this

Emily Glaser 1F

Why would a reaction be endergonic if the enthalpy is exothermic. Doesn't that contradict itself?

Emily Glaser 1F

9.7 uses the formula, deltaS = n C ln(T2/T1)
9.11 uses the formula, deltaS = n R ln (T2/T1)
What's the difference? Why

Emily Glaser 1F

Where does the third equation come from? The third equation being 2NO + 3/2O2 --> N2O5?

Emily Glaser 1F

Depends on the system. In this class, we usually deal with systems at constant pressure or constant volume, usually constant temperature too. So if you have a net production of gas (change in moles) than the pressure would increase in response to more frequent collisions. However, in this class, I w...

Emily Glaser 1F

Steam causes burns because the amount of heat that 100*C of gas has compared to 100*C of liquid is much higher because the heat of vaporization requires a lot of heat input before phase change (liquid to gas)

Emily Glaser 1F

Why is it okay/normal to put fractions in these equations to perform Hess' Law? For example, H2 + 1/2O2 --> H20

Emily Glaser 1F

When does delta H equal delta U?

Emily Glaser 1F

Why does delta U = 0 in an isothermal expansion. q=-w? Explain

Emily Glaser 1F

I don't understand how the net moles produced was 2/3.

Also, where did the 1/3 applied to the delta H come from at the end of the solution?

Emily Glaser 1F

Enthalpy of formation is a given, experimental value discovered in a lab. We can use these values to find enthalpy of reaction.

Emily Glaser 1F

In class, I questioned, "If volume is decreasing in a system, wouldn't the pressure increase as well?" Lavelle answered that the pressure would remain constant because the temperature would decrease, which would relive the tension of confined space. But, why is this? Why and how would the ...

Emily Glaser 1F

Why is it not final minus initial in this problem for p1v/rt - p2v/rt?

n1 - n2 instead of n2 - n1

Emily Glaser 1F

I meant to say "decreasing volume" after "In reality" ^

Emily Glaser 1F

Why can I not us the conversion ml to grams in this situation? It makes me use PV=nRT

Emily Glaser 1F

Why does a system cool when the volume is decreased? I am aware that we are dealing with constant pressure so it would have to cool to maintain constant pressure but how exactly does that happen? In reality, wouldn't decreasing the pressure increase atom collisions which then causes increase in ener...

Emily Glaser 1F

Think of a resonance structure, the C-H are bounded and when you have 3 moles of c2h2, you are not breaking those c-h bonds or forming. You are putting the c-c bonds together. Look up c6h6 on internet.

Emily Glaser 1F

In this question, it asks to find the enthalpy of formation of various substances, like H20. Why are the answers different than the enthalpy of formation found in Appendix A2. The delta H formation of H20 in this problem is -242kj In Appendix A2, the delta H formation of H20 is -285kj Both are in li...

Emily Glaser 1F

Does Delta U = q in this problem since there is no mention of work? Is there an assumption no work is done?

Emily Glaser 1F

During discussion!

Emily Glaser 1F

The heat of formation for N2 and O2 is zero because that is their most stable form

Emily Glaser 1F

In both of these homework problems, the solution manual provides necessary equations out of thin air: for 8.65, N2(g) + (5/2)O2(g) --> N2O5(g) for 8.67, H2(g) + (1/2)O2(g) --> H2O(l) Where do these equations come from? For question 8.65, I found the correct answer without using that equation. I wasn...

Emily Glaser 1F

It's safe to use joules throughout the math process in this section since R=8.314J/Kmol and since 1atmL = 101.325J.

For sig figs, I think it would be smart to always convert final answer to kJ

Emily Glaser 1F

Since potential energy is related to position, why, in an isothermal expansion, is there no potential energy change as molecules move further apart?

Emily Glaser 1F

Delta U means change in internal energy, but what does this mean in simple terms? When is delta U = 0?

Emily Glaser 1F

Explain

Emily Glaser 1F

Avoid putting a charge on the central atom. N should have a formal charge of zero. Also, are you sure N is in the middle?

Emily Glaser 1F

I know an acid produces a conjugate base, but what does this mean. Is the conjugate base, basic?

Emily Glaser 1F

In a rxn involving a strong acid, is the conjugate base weak?

In a rxn with weak acid,is conjugate base strong?

Emily Glaser 1F

Memorize :(

Emily Glaser 1F

In the case of the CO ligand, would I attach C or O to the central atom.

Emily Glaser 1F

Question 37

Emily Glaser 1F

NH4HS(s) <---> NH3(g) + H2S(g)

What would happen in PbCl2(s) was added to products side.

This is from Lyndon's practice test. He said would shift to the left. I thought added a solid would have no effect, even if it has nothing to do with compounds involved. He claimed Q>K

Emily Glaser 1F

If Kc is x at 400K, what happens when all the concentrations are halved.

On the practice test, Lyndon put square root x, but when I used numbers, I got 2x

Emily Glaser 1F

If he didn't mention it in class, I wouldn't worry about it.

Emily Glaser 1F

An unpaired electron acts like a magnet. So fluorine with 5 e in p subshell, because of its unpaired electron, is weakly attracted into a magnetic field, and is said to be paramagnetic. All of calcium's electrons are in filled subshells. It has no unpaired elecectrons and is, therefore, not attracte...

Emily Glaser 1F

v=h/m*wavelength is deBroigle, for everything other than photons

E=hv only applies to PHOTONS because photons travel at speed of light (c=wavelength*v)

Emily Glaser 1F

c2- has two extra electrons, therefore, it has a higher pulling power since more negative charge

Emily Glaser 1F

Hi Ally ;)

This question is talking about the bond polarity not the compound polarity. The dipole moments between Si and O are not equal. As a compound , yes, it is nonpolar

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