CHEMISTRY COMMUNITY

MingdaH 3B

if concentration is kept constant, then yes, a larger k results in a faster rate

MingdaH 3B

I'm pretty sure third order reactions won't be on the exam.

MingdaH 3B

Maybe double check the numbers you're using again? when I do 0.15*-2*96485/(8.314*298) I get the right answer

MingdaH 3B

That's what I do lmao

MingdaH 3B

the rate constant is a tool used to relate concentrations to the rate of reaction, and as such, is not affected by the concentrations.

MingdaH 3B

Yes. The anode is the side that is oxidized, and the side with lower concentration always receives electrons.

MingdaH 3B

k' is a constant generally used for the reverse reaction rate. It is similar to the concept of products over reactants, since the equation divides the rate at which products are formed over the rate at which reactants are formed.

MingdaH 3B

This is because of the bottleneck effect. for example, if you have a reaction that goes through steps a, b, and c in order, with B as the slowest step, then a bottleneck will occur. Basically, the original reactants will continually be processed through step a, but step b will cause for a buildup of...

MingdaH 3B

Basically, if the concentration of one reactant species is constant, then the rate law of rate = k [a][b] can be simplified to just rate = k' [a] where b is just assumed to be a constant. However, if the concentration of b is not much higher than a, or some other mechanism where the concentration of...

MingdaH 3B

You should just be able to plug values into [A]_t = [A]_0 * e^(-kt). using 20 mg, k = 7.6*10^-3 and t = 300 yields ~2 mg

MingdaH 3B

No, it only describes a concept in reaction rate and kinetics, but it doesn't change K at equilibrium. It may change how long it takes for a reaction to get to equilibrium however.

MingdaH 3B

first, you find the frequency factor by plugging all of the given values and constants into the Arrhenius equation, and then you solve for k by plugging everything into the equation again except changing T.

MingdaH 3B

the basic form of a natural log is ln(x) = y where e^y = x. From this, once you isolate the natural log, in order to find the concentrations inside the log (x), you should use this identity by setting both sides as exponents of the constant e

MingdaH 3B

anode is always oxidized, and the side with lower concentration will always be oxidized.

MingdaH 3B

You can add them in 5 because they're part of a cathode anode system, but standard Ecell is not a state function in either case.

MingdaH 3B

Based on the review stuff we've had, I'd expect one or two conceptual questions or something to do with the Arrhenius equation to be on it.

MingdaH 3B

Since pH is higher than the pKa, the acid will dissociate into its conjugate base and H+, and so its conjugate base will have a charge of -1.

MingdaH 3B

An increase in temperature is equal to an increase in kinetic speed and so would increase the collisions of the molecules. This increases the reaction rate. Besides this it shouldn't affect the catalyst, unless the catalyst is something that can be denatured by higher temperatures or something else ...

MingdaH 3B

The units for the rate of reaction are M/s. Accordingly, the units for the rate constant is dependent on the units of the reactant species, so where there is only one reactant species, the rate constant is /s for first order reactions and 1/M*s for second order reactions.

MingdaH 3B

To find the order, you have to use the equation rate = k [A]^x[B]^y[C]^z. I would start by comparing experiments 1 and 4 where A^x and B^y would be constant, so the resulting difference would be due to C^z, so you'd be able to solve for z. From there I would compare 1 and 2, where B^y is constant so...

MingdaH 3B

The method your TA showed you does work, although it may be slightly slower than the normal method.

MingdaH 3B

Cell potential does not depend on the moles of a single half reaction, but rather on the redox reaction as a whole

MingdaH 3B

it doesn't have to be M/s, as it depends on the order of the reaction. It is a simple constant that relates the rate of reaction to the concentration of reactants, and so the units come from changing one to the other.

MingdaH 3B

You are able to do exactly this, although it would be more efficient, albeit slightly more complicated, if you use 75/125 for the activation energy.

MingdaH 3B

you'll almost always get delta G formation in a problem, but its usually zero for molecules that are already in their lowest energy states, such as diatomic noble gases.

MingdaH 3B

What do you mean natural logs? I'm just assuming here, but if you're talking about the linear graph of ln(A) and time t, then yes. A reaction that has a linear graph between lnA and t is first order

MingdaH 3B

1G,1H,1I Discussion, Echem Review
If you search the above post and look for one posted by chem_mod, it'll show up

MingdaH 3B

The half life is the amount of time for half the reaction to occur. If the reaction rate is higher, it means the reaction happens faster, so then the amount of time to get to half of the final state would be shorter.

MingdaH 3B

If you're talking about this question:Calculate the reaction enthalpy for the synthesis of hydrogen bromide gas, H2(g) + Br2(l) → 2 HBr(g), from the following data - you know that enthalpies of reaction equations can be added together, multiplied, and subtracted.

MingdaH 3B

If you algebraically solve for x, you can cancel out x on both sides of the division equation on the right side, leaving you with 10 = 2/x, where x would equal 0.2

MingdaH 3B

Plug in the values into the equation 1/[A] = kt + 1/[A]0

MingdaH 3B

Frogs are cold blooded, so that, even with a great difference in temperature, since their own body temperatures won't compensate for a very cold environment, this reaction still has to occur for them to have vision, and so a reaction rate that has as small of a difference as possible would be evolut...

MingdaH 3B

Divide it into the partial reactions, where Cl is reduced and O2 is oxidized

MingdaH 3B

Balancing chemical equations bc ez

MingdaH 3B

The Arrhenius equation basically just relates the rate constant to temperature and the activation energy of the reaction.

MingdaH 3B

We don't need to know how to derive or integrate rate laws. Both measure the rate of a reaction, but a differential rate law relates this to the concentration of a species in the reaction while an integrated rate law relates this to an amount of time.

MingdaH 3B

Identifying the rate limiting step can be proposed / guessed from the reaction rate equation. Depending on the question, it may also be given in the problem itself.

MingdaH 3B

The different pathway may have a lower activation energy, but not necessarily. A different pathway can be a completely different set of sub steps per reaction that happen when a catalyst is added.

MingdaH 3B

We don't need to know the equations associated with collision theory, but you should have a strong conceptual understanding.

MingdaH 3B

Your units are fine, but I'm pretty sure n = 2, since there is a transfer of two electrons.

MingdaH 3B

A pseudo first or second order reaction is one that is not naturally first or second order with regard to that reactant, but, if another reactant has an relatively much larger concentration, it can be simplified to a pseudo-_____ order. You'd have to get a description of the actual experimental proc...

MingdaH 3B

I'm not sure where to find the question, but as for determining the rate limiting step, depending on the reaction rate equation, we can propose / guess which step of the reaction is the slowest, so long as it conforms to the reaction rate equation.

MingdaH 3B

Plugging the values given into the equation, E = -RT/nF *ln([Anode] / [Cathode]), we can find the concentration of the anode solution. We can also figure out part b from this problem through the same equation, where adding water to the cathode solution reduces cathode concentration, and halving the ...

MingdaH 3B

Your work looks right to me. Where is this problem from?

MingdaH 3B

If you still don't understand Le Chatelier's principle from the textbook's description, you can go to khan academy and try looking at some of his videos, and here's a youtube lecturer I find very helpful. https://www.youtube.com/watch?v=PciV_Wuh9V8

MingdaH 3B

From what I remember from lecture, I think Lavelle said that the final is cumulative

MingdaH 3B

heat transferred is equal to enthalpy when pressure is constant.

MingdaH 3B

Activation energy does not depend on the number of moles. If the number of moles goes up, then total energy goes up, as evidenced by the activation energy, but activation energy itself does not have anything to do with it.

MingdaH 3B

depending on a reaction, you may be able to guess what the slow step is just by looking at its chemical reaction. The slow step of an overall reaction is usually determined experimentally.

MingdaH 3B

Yes, for each mole of one reactant species consumed, you'll get one mole of any product.

MingdaH 3B

Which worksheet is this?

MingdaH 3B

There are a variety of problems where you can use the rate constant, such as when you have information about two of the following three, and are asked to find the third: rate constant, temperature, and activation energy of a reaction. Activation energy may be given.

MingdaH 3B

The rate of reaction is how quickly a reaction proceeds, or how much concentration of reactant(s) is consumed in some period of time. The rate constant is a constant, differing between different reactions, that relates the current concentration of reactants to the rate of reaction

MingdaH 3B

given the initial .030 mols of SO2 and O2, there should be 0.030 moles of SO3 and 0.015 moles of O2 remaining after the reaction goes to completion, since SO2 is the limiting reactant. The final amount of gas is the amount of O2 added with the newly created SO3.

MingdaH 3B

Standard just means that the reaction occurs at 25 degrees C and 1 atm. It's sometimes referred to as STP, or standard temperature and pressure.

MingdaH 3B

A reaction profile is a diagram that shows the change in potential energy over a reaction pathway / time of a reaction. It will normally go up, reaching a climax, before falling to either a higher or lower energy level than when it started.

MingdaH 3B

I think we do need to understand it since I remember Lavelle talking about it in lecture.

MingdaH 3B

The arrhenius equation relates the temperature to the rate of reaction. It can be written as k = Ae^(-E_a/RT)

MingdaH 3B

The answer is already in joules when you plug it into the equation. Writing the answer either way works, as long as you make sure that it is clear what the direction of work is.

MingdaH 3B

They describe two different properties of an expansion. Isothermic means that the gas has a constant temperature. A reversible expansion means one where the outside pressure is constant. A reversible expansion does more work in the case of that question.

MingdaH 3B

For example, you can have a reversible gas pump to constantly change pressure during a reaction.

MingdaH 3B

I got the same answers as you did, and the answer key looks like it isn't accurate.

MingdaH 3B

From our textbook:"in thermodynamics, a reversible process is one that can be reversed by an infi- nitely small change in a variable (an “infinitesimal” change). For example, if the external pressure exactly matches the pressure of the gas in the system, then the piston moves in neither directi...

MingdaH 3B

No, you can touch it.

MingdaH 3B

Magic Eight Ball says... Yes, Chemcomm always has practice tests.

MingdaH 3B

You could use it to charge another battery in the same loop, leaving it to discharge through a light when the first battery doesn't have any electric potential left.

MingdaH 3B

Magic eight ball says... ¯\_(ツ)_/¯.

MingdaH 3B

Heat is a measure of transfer of thermal energy between two entities. Work is the amount of energy, in one form or another, that is actually used to do a certain task.

MingdaH 3B

Pressure and concentration changes will change the forward and backwards reactions at a rate that keeps the value of K, while temperature will favor one or the other, changing the value of K.

MingdaH 3B

Technically, it does, but it's pH is at 7, and the concentration of hydronium and hydroxide ions are extremely low, and not significant enough to affect most things

MingdaH 3B

Any questions similar to those in the homework may be asked.

MingdaH 3B

Equilibrium concepts can be applied to many parts of chemistry. Acid base is an important one among many applications.

MingdaH 3B

The equivalence point can be used in conjunction with the known concentration / amount of titrant to discover the total concentration or amount of analyte.

MingdaH 3B

https://1drv.ms/u/s!AtgAaS7JRjhHghECTiLvJXatomz0

MingdaH 3B

The rule of thumb is that the equilibrium will respond in a way that counteracts the change. However, this doesn't give you an accurate representation, so the best way to do so is to recalculate using equations to determine equilibrium.

MingdaH 3B

Q calculations are only for aqueous solutions and gases, by definition.

MingdaH 3B

If it is only a change in concentration, Kc won't change, the equilibrium state, at least right when the concentration is added, will be different, but it will still tend to the same equilibrium constant

MingdaH 3B

The left and right portions are arbitrary, as, given a reversible reaction, you could switch both sides and the left directional reaction would now be the new right directional compound

MingdaH 3B

Given an ideal gas, you could use the ideal gas law to find it, but otherwise, with just the chemical compound, it would be impossible

MingdaH 3B

What ions and ligands should we have memorized for the final?

MingdaH 3B

A shorter wavelength or higher frequency = more energy. Intensity has nothing to do with the energy of the photon, but rather, it has to do with the amplitude of the wave which corresponds to the "number" of photons

MingdaH 3B

C = Wavleength * frequency is usually only used for light waves.

MingdaH 3B

A higher pOH value means that the solution is more acidic, as there are magnitudes smaller amounts of OH-

MingdaH 3B

Practice :(. For memorizing things, especially things that are applicable in problems, it helps most just to do a ton of problems where you name things and try your best to do each without referring back to your notes.

MingdaH 3B

For acid base problems, I usually just use my intuition, and it works out since you know that nitrate has a base form as a common ion

MingdaH 3B

Cyano is -cn while cyanato is -ocn

MingdaH 3B

pH measures the amount of H+ molecules in solution while pOH measures the amount of OH molecules. Basically, the higher the pH, the lower the pOH, and the more acidic. Vice versa, the higher the pOH, the lower the pH, and the more basic a solution is.

MingdaH 3B

Draw out the lewis structure of the molecule and use your knowledge of vsepr theory to see if the p-orbitals are hybridized in this case.

MingdaH 3B

yoooooooooo

MingdaH 3B

the shape, molar mass, and individual atomic electronegativity is generally what you'd need to determine IMF. IMF then determines boiling point / melting point, not the other way around. where can we find this info? I'm assuming Lavelle has touched upon this in lecture, but I can't be sure since I ...

MingdaH 3B

In answering the question, the hydrate isomer isn't relevant and can just be ignored.

MingdaH 3B

Hybridization works the same for all elements, although some are very difficult to find in a molecular form. Count the number of bonds between atoms, and then it's just the same process

MingdaH 3B

It's relatively simple to look at the lewis structure of a molecule and see whether or not it'll donate / accept protons for some molecules.

MingdaH 3B

Hydrogen bonding is an intermolecular force, while bonds are intramolecular forces and occur inside of molecules in the form of bonds. They all rely on the same fundamental forces, but are technically different things.

MingdaH 3B

the shape, molar mass, and individual atomic electronegativity is generally what you'd need to determine IMF. IMF then determines boiling point / melting point, not the other way around.

MingdaH 3B

They have the same repulsion effect

MingdaH 3B

N2O is linear while NO2 is bent, and so the latter is a polar molecule. Due to this, NO2 IMF's are stronger, and therefore would have a higher boiling point

MingdaH 3B

Anions are more polarizable since they have more electrons and therefore are easier to induce a dipole in

MingdaH 3B

just googline a VSEPR chart on google images will give you a lot that'll be helpful, i.e. https://images.app.goo.gl/uBwSDjsgjDuaAWr58.

MingdaH 3B

van der waals forces is a general term that includes all intermolecular forces. London dispersion forces is a type of van der waals force that occurs between nonpolar molecules with instantaneously occuring dipoles.

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