CHEMISTRY COMMUNITY

Chem_Mod

I think you are referring to the bomb calorimeter (fixed volume) problem. If there is no change in volume then w = 0.

Chem_Mod

An enzyme is a biological catalyst.

Chem_Mod

ATP coupling refers to the energy released ( $-\Delta G$ ) during ATP hydrolysis is coupled (used) to drive an unfavorable reaction ( $+\Delta G$ ).

Chem_Mod

If water is no longer the solvent then it is part of the equilibrium constant and therefore in the rate law.

Chem_Mod

Thank you.

Signing off for this quarter.

Super long day. Time to zzz.

Chem_Mod

Giselle1B wrote:"In a sports relay race, a chemical kinetics specialist runs slowly, and his group loses the race. When the chemical kinetics specialist is asked why he ran slowly, his reply was 'I always wanted to be the significant rate determining step.'

Good one!

Chem_Mod

AngelaZ 1J wrote:What do dipoles say in passing?
"Have you got a moment?"

:-)

Chem_Mod

Standard cell potential is the voltage measured under standard conditions and is therefore a constant.
I discussed this in detail in class.

Chem_Mod

Give the integrated rate law = Simply write down the answer

Chem_Mod

Some TAs have there own final exams next week. Therefore they won't grade until after finals week. Sometime after finals week Chem 14B grades will be submitted.

Chem_Mod

No I don't. :-)

Chem_Mod

Use the Nernst Equation. See homework example.

Chem_Mod

You are most welcome.

Time to rest up and prepare for your next final.

Chem_Mod

q = C delta T

Delta U = q + w

Fixed volume: w = 0

Therefore, Delta U = q

Chem_Mod

Sometime after final's week.

Chem_Mod

Sometime after final's week.

Chem_Mod

I did this in class.
:-(

Can give off three protons.

Chem_Mod

Yes. See my/your lecture notes.

Chem_Mod

The more positive the standard reduction potential the more favorable the reaction, and therefore is a strong oxidizing agent.

Chem_Mod

Because for 2nd order reactions the half life depends on the initial concentration.

Chem_Mod

Yes basic solution.

Chem_Mod

Please clarify your question.

Chem_Mod

Are you sure this is the correct question from the 6th edition textbook. The question I see is asking for an explanation regarding the Michaelis constant. There are no activation energies provided here.

Chem_Mod

Which two equations are you referring to?

Chem_Mod

When trying to determine which substance is reduced all you need to pay attention to add reduction potentials that you are comparing. The larger (less negative) reduction potential means that it is more likely to get reduced.

Chem_Mod

Heating a system results in an increase in thermal disorder. An increase in volume, which allows a substance to spread results in greater positional order. In comparing the contribution of either you have to see if temperature is increasing, volume is increasing, or both and use the change in entrop...

Chem_Mod

Typically, you would not be expected to calculate change in internal energy in this way. The change in internal energy = Q+W equation is more relevant. However, the equation you are referring is for kinetic energy of monatomic gases.

Chem_Mod

Yes, you would convert pKa to pKb using pKa+pKb=14 and then convert pKb to Kb using pKb= -logKb.

Chem_Mod

The hydrolysis of every chemical is not necessarily negative but for ATP in particular when you’re breaking a bond a lot of energy is released because that bond was very unstable.

Chem_Mod

What value are you taking about? If you’re asking why delta H is positive it’s because you are forming a very unstable bond that requires a lot of energy to form.

Chem_Mod

Well we know that a change in temperature affects the rate constant k based on the Arrhenius equation and the factor by which the rate constant k changes is the same factor by which the rate itself changes according to the rate law. Therefore, you just need to take a ratio of the Arrhenius equation ...

Chem_Mod

This is the integrated rate law for a first order reaction. The integrated rate laws tell you how much concentration of something you have left after some time has passed.

Chem_Mod

As a good rule of thumb always convert time into seconds.

Chem_Mod

Yes, you cannot use the ideal gas law for nonideal gases, solids, or liquids.

Chem_Mod

For a second order reaction, a plot of 1/[A] vs t should give you a straight line with a positive slope.

Chem_Mod

The solutions manual could technically choose any metal for the Au+ being oxidized to Au+3 reaction. They probably just decided to use Au since it's a metal that conducts electricity. But they could've used Pt or any other metal that conducts electricity. :)

Chem_Mod

You probably won't have to worry about any equation derivations on the final exam. :)

Chem_Mod

This is much more biological, but in relatively simple terms, the energy created by breaking the H off of NADH is used to drive the ATP reaction. :)

Chem_Mod

Once you calculate all the orders of the reactants, you would use this along with the rate of the reaction and initial concentrations of those reactants in order to calculate your rate constant, k. :)

Chem_Mod

electrolytic cell :)

Chem_Mod

It might be because you may need to use the molar heat capacity in several of the entropy formulas. When using the molar heat capacity for a substance in these equations, you must be able to convert the substance's mass into moles. :)

Chem_Mod

During a reversible expansion, typically a force must be applied for a longer period of time since during a slow reversible expansion, at every point in the expansion, the internal pressure of the confined gas must be equal to the external pressure of the surrounding gas(es). During an irreversible ...

Chem_Mod

You set up the rate law expressions for the different experiments and then you divide one rate law expression by another rate law expression in order to cancel out terms and get only one exponent that you can solve for, using logarithms if necessary. These exponents are the orders. :)

Chem_Mod

For monoatomic ideal gases, a change could be occurring under the conditions of constant pressure or constant volume. Based on the degrees of freedom for the atoms under constant pressure or constant volume, we'll see that the heat capacity values will be different for constant pressure and constant...

Chem_Mod

The specific heat technically changes with temperature; however, you do not need to concern yourself with these changes for the final exam. For all intensive purposes, yes, the specific heat for a given chemical species will be a fixed value. :)

Chem_Mod

The main function of the salt bridge is to prevent charge build-up. :)

Chem_Mod

The porous disk serves the same function as the salt bridge (prevent charge build-up). :)

Chem_Mod

You can typically use k' for any step in a multi-step mechanism. When you use k₁', it is the symbol for the rate constant of the reverse reaction for step 1 of the mechanism. :)

Chem_Mod

For K and Q, you are typically using the concentrations or partial pressures of the chemical species to write those expressions. But it's very difficult to define or even measure the concentrations or partial pressures of pure solids and pure liquids. It's much clearer how to measure the concentrati...

Chem_Mod

In this case, the P4 has an oxidation state (charge) of zero. On the right side, the P in H2PO2- will get an oxidation state of +1 and the P in PH3 will get an oxidation state of -3. So, P4 would be used as the reactant in both the oxidation and the reduction half reactions. From there, you will fol...

Chem_Mod

A bomb calorimeter is a closed system since it can't absorb or release energy from/to the surroundings and it also can't gain or lose mass to the surroundings. :)

Chem_Mod

Capital K is the equilibrium constant. It represents the value you get when you divide concentrations of the product(s) by the concentrations of the reactant(s) once the chemical reaction has reached a state of chemical equilibrium. :)

Chem_Mod

You probably won't have to worry about deriving equations on the exam. :)

Chem_Mod

I think what you're referring to is that when you have to calculate the E value for a reaction like this: Ti +4 + 2e- -> Ti +2 , you cannot simply add the E values for the reactions Ti +4 + e- -> Ti +3 and Ti +3 + e- -> Ti +2 . The details about why this happens aren't too important, but this is a g...

Chem_Mod

While the formula sheets vary from year to year, it's likely that if these half-life equations were on the most recent exam, they will be on the final exam formula sheet. :)

Chem_Mod

Not quite, because k₁' can represent the rate constant of the reverse reaction for step 1 in a mechanism. But, k' in pseudo rate kinetics often will be equal to k*[some reactant]. :)

Chem_Mod

One could set the unique rate of reaction equal to the rate law derived from a mechanism since both are mathematical expressions of the overall rate of the reaction. :)

Chem_Mod

If and only if that particular reaction is an elementary reaction (meaning it's a reaction for one step in a mechanism), then yes, the coefficients in the balanced chemical equation will become the orders of those reactants. :)

Chem_Mod

Turns out that Gibbs free energy is an extensive property. :)

Chem_Mod

I think this may be due to you using log instead of ln? On the equations sheet for the nearest equation they use ln. Which should we use? Hi Elle, You can use both. Please be aware that the difference is 0.0592 for log and 0.0257 for ln. If you plug in the number into two equations (in attachment),...

Chem_Mod

Activation energy is the delta G value between a reactant and a transition state. So you could say that the delta G for the overall reaction = delta H of the reaction - T*(delta S of the reaction). But otherwise, there isn't an equation which relates the activation energy and delta H. :)

Chem_Mod

The reason isn't too important. What's important is that you know that for a galvanic cell, the notation for a porous disk is a single vertical line and the notation for a salt bridge is 2 vertical lines. :)

Chem_Mod

Yes, it's definitely good to know about the enthalpies associated with the phase changes (melting, boiling, freezing, etc.). :)

Chem_Mod

The units for deltaS is units J/K

Chem_Mod

Delta H is typically in joules or joules/mole

Chem_Mod

A is the pre-exponential or frequency factor which essentially gives you the proportion of reactants that collide in the correct orientation and with enough energy in order to form products.

Chem_Mod

Yes you can solve for the units of the rate constant k because you know that the units for rate is molarity/second and the units for concentration is molarity, therefore the units for the rate constant k changes depending on the exponent of the concentration.

Chem_Mod

It's either in Joules or Joules/mole

Chem_Mod

Molecularity is calculated by the number of molecules that must react with each other in order to form your products. Important thing to note is to realize that the stoichiometric coefficients must be accounted for in calculating molecularity.

Chem_Mod

What profile are you talking about. Are you referring to the rate law plots?

Chem_Mod

Work is 0 when there is no change in volume (isochoric). Heat is 0 for an adiabatic process, which will usually be explicitly stated.

Chem_Mod

Sum of bonds broken - sum of bonds formed because this is essentially the amount of energy you are putting into the system to break bonds - the amount of energy that is released by the formation of new bonds.

Chem_Mod

In general, you want to include the anode, cathode, ions, salt bridge, and direction the electrons are traveling.

Chem_Mod

Thank you all your thoughtful and encouraging messages.

Posting that video was great!

A Big Thank You for the Valentine Cappella.
A first and most appreciated.

Great Quarter!
Great Classes!

Chem_Mod

WOW.

Many great photos!
:-)

Many Thanks to All!

You Rock!

Chem_Mod

I am not sure what you are referring to.

Chem_Mod

No you do not. A coulomb is the fundamental unit for a charge.

Chem_Mod

It will be clear what the constants that you are given represent.

Chem_Mod

Please post the problem.

Chem_Mod

Kelvin is the standard unit for temperature. As a good rule of thumb always have your temperature be in Kelvin.

Chem_Mod

Please be more specific. Post the problem and part you are stuck on.

Chem_Mod

Heat capacity are in those units so that you can multiply it by whatever the mass of your total object is giving you the heat capacity for that object or piece of matter.

Chem_Mod

Ka and K are the same thing. Ka is just the equilibrium constant for an a reaction in which an acid is reacting.

Chem_Mod

The entropy of formation is 0 because they are elemental molecules, meaning this is how they are found in nature, therefore there is no entropy change associated with them being formed.

Chem_Mod

For endergonic reactions the reactant has a lower Gibb's free energy value than the products, which makes sense because when you take the gibb's free energy of the products - reactants you get a positive change in gibb's free energy. For an exergonic reaction, the reactants have a higher gibb's free...

Chem_Mod

Le Chatelier's Principle states that the reaction will lean toward the side that opposes the change that has just occurred. For example, if you increase products then the reaction will lean to the left and products will turn into reactants, decreasing products. If you decrease products, the reaction...

Chem_Mod

It comes from the equation $\Delta G = \Delta G^o +RTlnQ$
When the reaction is at equilibrium $\Delta G$ is equal to 0 and Q turns into K.

Chem_Mod

These are some great tips! Some things I would add: 1) If you ever run into a question you have no idea how to tackle, think about the concept it's trying to test. Try to note anything that you remember about that concept. Usually that tells yourself that you do know something. It just may take some...

Chem_Mod

Please be more specific, posting the problem would be very helpful.

Chem_Mod

I do not believe Dr. Lavelle stated the average.

Chem_Mod

HA and A^- are just examples of an acid/base reaction, where HA is any acid and A^- is its conjugate base. Know that Ka and Kb are the equilibrium constants for acids and bases respectively and that strong acids/bases do not have Ka/Kb because they dissociate completely.

Chem_Mod

When the pressure is constant the work does not equal the change in volume. The equation for an irreversible expansion is W=-nRTln(V2/V1).

Chem_Mod

Hi Whitney,

You are absolutely correct. That negative should be an equal's sign. Good job!

Chem_Mod

In mechanisms, intermediates are chemicals introduced to us as products and then used up as reactants in later mechanism steps. For example:

A + B -> C + D
C + E -> F
D + G -> H

In this scenario, C and D are the only intermediates.

Hope this helps! :)

Chem_Mod

Most likely, that would be true. I'm sure other factors are involved, but if heat is transferred from the surroundings to the system, since S = q rev/T, we'd probably expect an increase in entropy (disorder). :)

Chem_Mod

You can treat bar and atm as almost the same thing, but if you want to be super safe, you can use that conversion factor to convert atmospheres into units of bar. :)

Chem_Mod

In general, it's a good idea to start with the pairs of experiments where only one reactant's concentration is changing while the other concentrations are held constant. Looking at experiments 1 and 2, we see that both [A] and [C] are changing.

Hope this helps! :)

Chem_Mod

In the case where the first step of the mechanism is the rate determining step, then yes. But in other cases, that's probably not going to be true because other k terms will be introduced if you have to use the pre-equilibrium approach to get rid of intermediate terms in the overall rate law express...

Chem_Mod

A monoatomic ideal gas can be under conditions of constant T, constant P, and/or constant V, depending on the system presented to you. A monoatomic ideal gas is just an ideal gas (obeys PV = nRT) which has only 1 atom (Ne (g), Ar (g), etc.)

Hope this helps! :)

Chem_Mod

You most likely won't be asked to derive the integrated rate laws on the final exam.

Cheers! :)

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