CHEMISTRY COMMUNITY

Leonardo Le Merle 1D

I will not have access to a printer in that 3 hour timeslot; if a TA or someone could clarify how we are meant to turn in the final that would be very helpful.

Leonardo Le Merle 1D

That link didn't work :(

Leonardo Le Merle 1D

Just to ensure I didn't mix up anything I usually convert everything to seconds before trying to solve the problem - if it asks to be expressed in minutes or hours you can convert back at the end.

Leonardo Le Merle 1D

The answers to this question
viewtopic.php?t=25381
Were also pretty helpful for me sorting it out in my head, hope they help!

Leonardo Le Merle 1D

I'm confused in what situation we would have to incorporate temperature in our solutions to kinetics-based questions. It seems that for many questions, rate constants are not affected by a provided temperature, but I know that reactions occur faster when temperature is increased. In what type of que...

Leonardo Le Merle 1D

An example for the above reply would be in the case of CH3OH + (3/2)O2 = CO2 + (2)H2O...
You'd multiply both sides by 2 to get (2)CH3OH + (3)O2 = (2)CO2 + (4)H2O

Leonardo Le Merle 1D

They DO have internal energy, but there is no change in internal energy. Basically, because ideal gas are extremely non-reactive particles (already fully stable), they don't "see" each other at all. The average kinetic energy is nothing else than the temperature of the ideal gas, and if th...

Leonardo Le Merle 1D

Thank you so much! Very helpful.

Leonardo Le Merle 1D

Is rate always expressed with seconds as the measurement of time? Or could a rate law be expressed in M/hr?

Leonardo Le Merle 1D

Could there ever be a reaction in which all reactants are zero order and thus the reaction itself is zeroth order? What would be an example of this?

Leonardo Le Merle 1D

For 7A. 11, should we ignore the mention of the reaction occuring at 700 K? If not, I'm unsure of how to incorporate this into the rate law.

Leonardo Le Merle 1D

A note on delta U being expressed the change in internal energy; (U=w+q); w is often expressed interchangeably as work done on the system and work done BY the system. For the former, it is w+q; for the latter, it is actually -w+q because the work done by the system is still positive but it results i...

Leonardo Le Merle 1D

Although electric vehicles are not entirely zero emission, they ultimately convert over much more of the energy from fossil fuels power at the wheels. Conventional gasoline vehicles only convert a small fraction of the energy stored in gasoline to power at the wheels

Leonardo Le Merle 1D

My AP Chem teacher was an Ozzy and always used: Kangaroos Hop Down Mountains Drinking Choccy Milk. Not that one's better than the other, but I've always remembered it through that acronym :)

Leonardo Le Merle 1D

It's a good idea to memorize which bases and acids are strong so you can know exactly when to apply the above methods mentioned.

Leonardo Le Merle 1D

This is a feature of Le Chatelier's Principle; I think it should be in Week 3 notes if that helps!

Leonardo Le Merle 1D

Zeroth order: M * s^-1
First order: s^-1
Second Order: M^-1 * s^-1
etc.

Leonardo Le Merle 1D

It helps me to isolate the reactant's effects on rate in an algebraic format.
2A = 4
2A*2B=8
Where A and B are the reactant's orders.
Therefore A must equal 2 and B must equal 1.

Leonardo Le Merle 1D

Kelvin = Celsius + 273.15; the two are on the same scale so converting between the two isn't too tricky.

Leonardo Le Merle 1D

Also, note that just because a reactant is first order, doesn't necessarily mean the reaction itself is as well. If multiple reactants are first order, the reaction is the sum of those reactants (So if N and O were both first order in forming NO, the reaction is second order).

Leonardo Le Merle 1D

Also it might be a good idea to memorize the y-axis for various orders of reactions (zeroth [A], first ln[A], second 1/[A])

Leonardo Le Merle 1D

Also, if you are given various rates provided reactant concentrations, and rate does not change as a reactant concentration is increased or decreased, you know it is zeroth order. If it changes proportionately, it is first. If it changes exponentially, it is second or third or above.

Leonardo Le Merle 1D

The above post also applies for third order reactions; M would be squared in the denominator.

Leonardo Le Merle 1D

You can identify a reactant as zero-order if changing its concentration does not affect the rate in any way.

Leonardo Le Merle 1D

It should be noted that some balancing is necessary to identify n, which is the balanced amount of electrons between the two redox reactions. For instance, with an oxidation that loses 2 electrons and a reduction that gains 3, n would be 6. I would

Leonardo Le Merle 1D

I heard review sessions might be Bruincasted in some manner but nothing is set in stone until Dr. Lavelle emails us.

Leonardo Le Merle 1D

Should standard reaction Gibbs free energy be expressed in joules (or kJ) per mole? Or simply in joules alone?

The textbook says the latter, whereas the solutions manual says the former.

Thanks

Leonardo Le Merle 1D

Since the reaction doesn't specify, we can assume T=298K (room temperature). However, this is a typo on the textbook's part; they should have specified T.

Leonardo Le Merle 1D

a) (1.25mol S8) * (358.8 kJ/1mol S8) = 448.5 kJ
b) (197g C) * (1mol C/12.01g C) * (358kJ/4 mol C) = 1471.35 kJ
c) (415 kJ/358.8kJ) = (x mol CS2/4mol CS2); x = 4.63mol CS2

Leonardo Le Merle 1D

I've been looking at past study guides and one question kind of threw me off, as 10^-6.1 is used for both K and [H3O+] H3O+(aq) + HCO3− (aq) ⇌ 2H2O(l) + CO2(aq); K = 7.9 × 10-7 This reaction assumes that all H2CO3 produced decomposes completely to CO2 and H2O. Suppose that 1.0 L of blood is brought ...

Leonardo Le Merle 1D

I found this question from a study guide from a few years ago and was hoping someone could explain the answer (in bold).

For a 0.10 M solution of a weak acid, HA, with pKa = 10, which of the following is true?

[HA] ≅ 0
[HA] = Ka
[HA] = [A−]
[HA] ≠ [H3O+]
[HA] = [H3O+

Leonardo Le Merle 1D

What are we meant to use if it is not reversible expansion?

Leonardo Le Merle 1D

Also adding onto this question if that’s okay, do adiabatic and isothermal mean the same thing?

Leonardo Le Merle 1D

Can someone clarify what exactly an irreversible expansion would look like? As in explain it with an analogy; something besides the piston one.

Leonardo Le Merle 1D

This can become sort of confusing as U is said to equal both Q+W and Q-W; just try to keep in mind that internal energy is lost if the system DOES work; in the first equation this would mean W is negative and in the second it would be positive. Both mean the same thing.

Leonardo Le Merle 1D

The equations U=Q-W and U=Q+W are used interchangeably; instead of memorizing one or the other it helps to think about whether work is being done BY the system (in many contexts, expansion of a gas) or TO the system (compression).

Leonardo Le Merle 1D

°C = K + 273.15; there is no multiplication involved and thus the scale is proportional.

Leonardo Le Merle 1D

I also had confusion with this part of the lecture as I'm currently in Math 3B and we haven't covered integrals yet; if someone could clarify what exactly v1{v2 means that'd be great.

Leonardo Le Merle 1D

d is an open system because matter is allowed to exit the engine through the exhaust in the form of CO2

Leonardo Le Merle 1D

Think about the energy of the gas; because a force is being exerted on it (W), that results in an increased pressure and energy (U) in that system - it might heat up as a result.

Leonardo Le Merle 1D

I may be misunderstanding definitions, but how can a bomb calorimeter be an isolated system if energy is allowed to transfer to the water? Doesn’t an isolated system mean matter and energy exchange is not allowed?

Leonardo Le Merle 1D

Yes. That equilibrium could technically be 0, meaning no product forms, or an infinitely large value, meaning all reactants turn into product, or some intermediate value of the two. In any case, some equilibrium will generally be reached in my knowledge.

Leonardo Le Merle 1D

Buffers are generally made of certain pairs of solutes, either a weak acid plus a salt derived from that weak acid or a weak base plus a salt of that weak base. For example, a buffer can be composed of dissolved acetic acid (HC 2H 3O 2, a weak acid) and sodium acetate (NaC 2H 3O 2, a salt derived fr...

Leonardo Le Merle 1D

There is no unit for Kc or Kp, it is simply a value used to represent the ratio of product and reactant concentration at equilibrium

Leonardo Le Merle 1D

It should be added that when steam condenses on skin it adds to the amount of energy; it’s the joules from the phase change that releases so much energy.

Leonardo Le Merle 1D

Quadruple bonds technically are possible but they require the presence of four different orbitals (two S, one P, and one D); carbon cannot attain the last.

Leonardo Le Merle 1D

Try emailing your high school teacher and seeing if they can forward you a document with all their old slides; more sources = more information, can’t hurt!

Leonardo Le Merle 1D

It is important to note that PV=nRT only stands true if the increase in pressure changes concentration; adding an inert gas such as helium to the system will increase the pressure but make the volume remain the same, thus no change in K occurs.

Leonardo Le Merle 1D

Thank you for the advice!

Leonardo Le Merle 1D

That's what I used for this question, personally.

Leonardo Le Merle 1D

It's essentially describing how H2O is also being converted into H3O+ and OH-, but at extremely small concentrations compared to the much more stable concentration of H2O.

Leonardo Le Merle 1D

Depending on the type of reaction (endothermic or exothermic), temperature affects K differently, increasing it for endothermic ones and decreasing it for exothermic ones.

Leonardo Le Merle 1D

When calculating K, should we always express it for gases in terms of partial pressure? Or should we try to convert to concentration (n/V) for them as well?

Leonardo Le Merle 1D

+ X is generally used for products and - X for reactants, as the former is produced from reaction and the latter is used up. However, I'm sure it depends on the context of the question.

Leonardo Le Merle 1D

I agree, thank you so much!

Leonardo Le Merle 1D

Try to control your breathing between questions, it will slow your heartrate and calm you down!

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