CHEMISTRY COMMUNITY

Nathan Tu 2C

If activation energy is reached in the reactants, then when the reactants collide to form a product or intermediate, they will form the product/intermediate. Without reaching the activation energy required, reactant collisions will temporarily create the product but then reverse back into reactants ...

Nathan Tu 2C

Typically, if a proposed mechanism has multiple steps, if there is a product produced in step one and used as a reactant in a later step, then that product is an intermediate.

Nathan Tu 2C

If they do not tell you the slow step, then you would have to be given the rate law and try to find the slow step. In other words, you will always be given the rate law or the slow stop.

Nathan Tu 2C

Half life equations differ based on rate order. The half life equation for a zero order reaction is different from the half life equation for a first order or second order equation.

Nathan Tu 2C

We could also be given a graph and be asked whether reaction is zero order, first order, or second order to a particular reactant. For example, if the concentration decreases exponentially over time with respect to a particular reactant, then the reaction is second order to that reactant.

Nathan Tu 2C

The instantaneous rate is the rate at which concentration is changing at that one specific moment in time and is noted by d[concentration]/dt. The rate of the reaction is referring to the overall rate of the reaction, or how fast the general reaction is. It is denoted by change in concentration over...

Nathan Tu 2C

It does matter where we draw the tangent line because in most reactions, the rate decreases as the reaction proceeds. This means that the initial rate is higher than the rate near the end of the reaction which also means that the slope of the tangent line will be greater as well near the beginning o...

Nathan Tu 2C

If the cell is not a galvanic cell, or rather the case in any cell, subtract the E anode from E cathode which means subtracting the E of the oxidation reaction from the E of the reduction reaction. If the answer is not positive, than the cell is not a galvanic cell.

Nathan Tu 2C

I would also like to add that k has different units for each type of order reaction. For example, k is in M/Ls for zero order equations and inverse seconds for first order equations. To find the units for k, set the reaction equal to M/Ls and solve for whatever units allow the units to end up as M/Ls

Nathan Tu 2C

We use H+ to balance redox reactions because its easier. With H3O+, we have extra oxygens we have to balance so it would make reaction balancing harder.

Nathan Tu 2C

If you are given the cell diagram, locate the cathode and anode, write the half reactions that occur at each electrode, then combine the balanced half reactions into one equation. If the other way around, split the reaction into half reactions. Identify what is being oxidized and reduced and put the...

Nathan Tu 2C

Concentration cells are special in that they create electricity because of only a difference in concentration. The difference in ion concentration drives electron flow because the system wants to reach equilibrium. There is only a difference in concentration because it is the same solution.

Nathan Tu 2C

There may not be always be an increase in entropy. Since spontaneity is given by the formula deltaG= delta H - TdeltaS, if change in entropy is negative (a decrease in entropy), then reaction can be spontaneous if delta H is negative. This is only possible only at low temperatures. However, most rea...

Nathan Tu 2C

Increase in vibrations increases entropy because it increases the possible states that the individual atom can have.

Nathan Tu 2C

To add on to that, it should be noted that reversible reactions have provide the maximum amount of work where as irreversible reactions provide substantially less since there is energy loss to heat, friction, etc.

Nathan Tu 2C

In an equilibrium reaction, delta G is equal to zero when the reaction reaches equilibrium. This is because at equilibrium the free energy of the reactants equals the free energy of the products, making the difference in free energy zero.

Nathan Tu 2C

Both affect whether the reaction is spontaneous. Since gibbs free energy is dependent on the enthalpy and entropy, they both help determine whether the reaction is spontaneous. Given certain combinations of enthalpy and entropy values, the temperature can help determine whether the reaction is spont...

Nathan Tu 2C

It refers to the gibbs free energy, which is partly dependent on enthalpy. In a sense, its both, but the specific criteria we use to determine whether a reaction is thermodynamically favored is gibbs free energy.

Nathan Tu 2C

I think this is how it works. An irreversible expansion is essentially all real life expansions. The change in volume occurs so quickly that it is essentially instantaneous. In the case of an reversible expansion, the instantaneous change in volume dV, is essentially zero, I think but it might be a ...

Nathan Tu 2C

Work is a method of transferring energy. When work is done on the system, it has a positive value because the internal energy increases. When work is done by the system, it has a negative value because the internal energy of the system decreases.

Nathan Tu 2C

An easy way to see that this is a closed system is to ask yourself two things: "is matter leaving or entering the system?" and "is energy entering or leaving the system?" In this case, unless there is a leak in the ice pack, the contents of the ice pack are not intended to escape...

Nathan Tu 2C

In terms of general stability, molecules are more stable when they have higher bond enthalpies. This is because the higher the bond enthalpy, the more energy is required to break that bond. With regard to this problem in particular, the Kekule structures, I think, are referring to the resonance stru...

Nathan Tu 2C

No, I do not believe so. If I remember correctly, on Friday, he said we will not need to know about reversible processes as we will go over it on Monday.

Nathan Tu 2C

I believe in the latest email, he said we will not have work and internal energy questions on the test. Anything that deals with work will mostly consist of concept question. Anything concerning reaction enthalpy is fair game though.

Nathan Tu 2C

For the standard reaction enthalpy definition, it does not matter what the pressure or temperature is. It refers to a specific reaction enthalpy value at a constant pressure and constant temperature. Naturally, this implies that the values change with temperature and volume. However, most people jus...

Nathan Tu 2C

We describe enthalpy in terms kj. When we talk about a reaction, the kj/reaction is implied. When we talk about kj/mol, we are referring to kj per mole of that substance.

Nathan Tu 2C

Work and heat are related by the fact that they both involve energy. Work is the energy required to do "something" and then heat is thermal energy. Thus, we can derive formulas relating work to heat is based on the conservation of energy.

Nathan Tu 2C

With that set, it is definitely only one electron with that set of quantum numbers. Four numbers are always required to describe one specific electron.

Nathan Tu 2C

Judging from what Lavelle lectures, I would assume it's always referring to Kc. However, during the final, if its a question involving all gases and its unclear, I would ask the TAs proctoring the exam. After all, they are there to clarify any questions.

Nathan Tu 2C

There is no difference in the formulas themselves. It is just that K specifically refers to when the reaction is at equilibrium and Q refers to any moment of time aside from that.

Nathan Tu 2C

It can act as an acid and base in the bronstead (I think I spelled that right) definition. It can donate a proton to OH compounds, like NaOH. It can also receive a proton, like with HCl to form H^3O.

Nathan Tu 2C

For the difference between sigma and pi bonds, they are different in length and strength sigma bonds are longer than pi bonds and are weaker. Pi bonds are stronger. Also, in sigma bonds, the atoms involved can rotate. In pi bonds, they cannot.

Nathan Tu 2C

Common polyatomic ligands you will have to just memorize. However, you can determine the charge of a monoatomic ligand, like Cl, by looking at the charge their ion would have.

Nathan Tu 2C

After counting how many electrons I have, I always like to look at the name and try to base my model around that. For example, the only way you would arrive at the structure for CH^3SH and HOCO would be by looking at the name and basing your structure around that.

Nathan Tu 2C

In terms of difficulty, drawing out the lewis structure, is in my opinion, probably the easiest way to know the bond angles. That way you can see visually the number of lone pairs and bonds on the atoms.

Nathan Tu 2C

Any element with an atomic number less than carbon( aka Li, Be, He, B, and H) can have less than an octet. This is because it requires less energy to have just their s orbital filled than to gain an more electrons to get an octet. Group 3 and below non metals like phosphorus can hold an expanded oct...

Nathan Tu 2C

There are two hints that tell you that hydrogen is attached to oxygen. One is the name since it is next to oxygen in the name. The second part is after calculating formal charges, it would become apparent that H should be attached to O. It makes it more stable to have it on oxygen than on carbon in ...

Nathan Tu 2C

The electron configuration for Beryllium is 1s^2, 2s^1. It has no electrons in the p orbital. In order to get a full octet, it would need to gain 6 e-. This requires more energy than giving away one electron and simply having 2 electrons in the 1s orbital like helium, which is an stable inert gas. T...

Nathan Tu 2C

First, ammonium is NH4^+, not NH3. Also, if I remember correctly, compounds are always ionic in nature. Therefore, in ionic compounds, the ions are not connected because they are not sharing electrons. The anion took the electron (or electrons) from the cation. Therefore, they share no electrons and...

Nathan Tu 2C

What do you mean by problem? Do you mean formula? Either way, out of the equations we went over in class, de broglie's equation, wavelength is equal to the planc's constant divided by momentum, has velocity because momentum is mass times velocity.

Nathan Tu 2C

The simple answer is that the energy difference is that the energy difference between 3d and 4s is so small, filling up 4s first happens to be more stable. With exception of Cu and Cr and elements similar to those.

Nathan Tu 2C

Memorizing the prefixes is helpful, but not necessary. Most answers are fine in SI units. However, knowing the prefixes will help you check your answer. For example, for wavelength, you would expect to have your length to be in nanometers.

Nathan Tu 2C

Generally, Dr. Lavelle will let you know what is on the test. From what I've seen, its mostly concepts gone over in class and how well you can use those concepts. Like how well you can manipulate equations and the meaning behind them.

Nathan Tu 2C

Essentially they are the same thing. The work function describes the work being done to remove an electron. Since work requires energy, it can be said that the threshold energy is the energy required to do the work of removing an electron.

Nathan Tu 2C

As to why c is the correct answer, there is a mathematical explanation. Lets say you have a light wave that behaves as the function sin (bx). In this function, b affects the frequency of the wave and is a constant. If you play around with values for b and graphed the resulting equation, you'll notic...

Nathan Tu 2C

Well since you found out how many molecules you have, it is important to note that is your initial amount of molecules. Since initial amount should equal final amount, because number of moles/ molecules should not change when diluting a solution, the initial amount is the final amount. Thus your 6.0...

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