CHEMISTRY COMMUNITY

Naveed Zaman 1C

In case you are wondering, ln(k) = ln(A) - (Ea/RT) is just another way of writing the original Arrhenius equation in the exponential form (we just took the natural log of both sides to get this new equation). Since generally we use experimental data in the form of a graph to determine E a , we usual...

Naveed Zaman 1C

There would have to be more information give to you. You cannot make an assumption or an estimate based solely off the information they give you in the problem. Therefore, when you draw the graph, the E a for either Step 1 or Step 3 can be higher, but there just isn't enough to make a judgement abou...

Naveed Zaman 1C

You're going to draw what the transition state will look like. Basically, it'll look like a variation/combination of whatever the reactant molecules they give you are. All the bonds in the transition states are draw with dotted/dashed lines instead of solid lines because we are representing these bo...

Naveed Zaman 1C

You have to balance the half reactions to get an overall redox reaction. In this case, the half reactions are already balanced, so the reaction is AgCl(s) + I-(aq) -> Cl-(aq) + AgI(s). So I- is a reactant and Cl- is a product, and Q = [Cl-]/[I-] (remember that solids are not included in this reactio...

Naveed Zaman 1C

w = -P_extΔV (the sign if negative because this is the work that the system is doing)

Naveed Zaman 1C

Basically, catalysts can turn some reactions into zero order reactions because of their very nature to facilitate collisions. A reaction that is second order, such as the decomposition of NO 2 to N 2 and O 2 , can be turned into a zero order reaction in the presence of a hot platinum wire (which act...

Naveed Zaman 1C

I think that's the right answer. The book might just have the wrong answer. If you follow all the steps in the solutions manual, you should end up with e¹⁵ = 3269017, not 10⁶

Naveed Zaman 1C

I can't exactly remember what the curved graph was for, but I can take a guess. The linear graph depicted a first order reaction, where the natural log of the concentration of A (ln[A]) was plotted against time. This was called the integrated rate law for the first order reaction. Since the integrat...

Naveed Zaman 1C

A differential rate law is just an equation that shows what happens when you have a certain concentration of reactants (rate vs. concentration), and it has the form Rate = (1/a)(d[A]/dt) for a reaction A --> P (Get it? Since it's a differential equation, we are concerned with the rate of the reactio...

Naveed Zaman 1C

This is an example of a concentration cell. Since the only thing changing in this reaction is the concentration of H + , the "equation" is: H + (10 -3 M) --> H + (10 -4 M) There is only e- being transferred per mole equivalent of this reaction. If you wanted to do the half reactions, you w...

Naveed Zaman 1C

Since a cell only works if the overall cell potential is positive, we use this info to figure which of the two electrodes are the anode and which is the cathode. Since tin has a lower cell potential than hydrogen (hydrogen has the abbreviation for S. H. E. in the manual, standing for Standard Hydrog...

Naveed Zaman 1C

In this equation, some of the Au+ is being oxidized to Au3+ and some of it is being reduced to Au. You set up the half reactions similarly, with Au+ taking part in both half reactions: Reduced: Au + + e - --> Au Oxidized: Au + --> Au 3+ + 2e - Balancing the equation yields 3Au + --> 2Au + Au 3+ I'm ...

Naveed Zaman 1C

In a constant volume calorimeter, there is 0 work done since there is no volume change. For constant pressure calorimeters, there is work done by the system. This is because expansion/contraction can be done against a constant pressure. In constant volume calorimeter, q = ΔU since no work can be don...

Naveed Zaman 1C

Gibbs Free Energy is the amount of energy that is available to do work. A reaction that has a negative free energy value means that it can do work, whereas a positive free energy value means that a system needs to have work done to it. In the context of chemical reactions, negative values indicate t...

Naveed Zaman 1C

Yup you can assume that, unless there's a specific condition stating that temperature is constant, such as when a system is isothermal (meaning that the heat that is inputted is cancelled out by the system doing work so that there is no temperature change).

Naveed Zaman 1C

Each beaker has a solution of respective ions for each electrode metal. So in a beaker with a zinc electrode, the solution it is in will contain Zn 2+ ions. If it is a copper electrode, the solution contains copper ions. Of course you can't usually get pure metal ions on their own; they had to have ...

Naveed Zaman 1C

Since entropy is a state function (doesn't matter how we get to the final state), we can take a rather strange approach to get to the answer. We need to have 3 steps in our process: 1) heat the liquid water from 85°C to 100°C, 2) vaporize the water, 3) cool the water vapor from 100°C to 85°C. Theref...

Naveed Zaman 1C

The answer key doesn't use C of any kind... Are you perhaps looking at the wrong problem?

Naveed Zaman 1C

That is essentially what we would do, but it is more likely that we have to factor in phase changes rather than pressure changes (since we just have to look up values for phase change enthalpies). For the most common elements/molecules, you should probably know what their standard states are at 298K...

Naveed Zaman 1C

It might not be included in a diagram that's provided to you. Basically, a salt bridge just helps to keep electrons flowing throughout the cell. Without a salt bridge, the electrons would flow from anode to cathode and would build up in the cathode portion. Eventually, since all the electrons are al...

Naveed Zaman 1C

The product molecules that are formed are in the "liquid" phase (it is an aqueous solution). Since we are going from gases, which have high entropy since they can occupy many different microstates/positions, to liquids, which can occupy fewer microstates, the entropy is decreasing.

Naveed Zaman 1C

It's just an explanation for how to calculate entropy for certain reactions. We don't worry about whether a reaction can only go in one way or another. This allows us to do things like find the entropy for reactions that are not necessarily common. Again, it has to do with the fact that entropy is a...

Naveed Zaman 1C

I believe the solutions manual says that you just assume 1 mole of nitrogen gas (it's not mentioned anywhere in the problem).

Naveed Zaman 1C

If a reaction is spontaneous at a certain temperature, its reverse reaction is probably nonspontaneous at the same temperature, but this is more of a general statement than an actual rule or relationship.

Naveed Zaman 1C

Since w = P(deltaV) usually works in the units of Pascals for pressure and m 3 for volume, we need a conversion factor to account for the fact that the pressure given in the problem is in atmospheres. This is done in one of two ways. 1) convert atm to pascals (101325 pascals = 1 atm), convert cm 3 t...

Naveed Zaman 1C

You have to look up enthalpies for liquid water versus ice (solid water), and do the following:

deltaH_liquid - deltaH_solid = deltaH_fusion

Naveed Zaman 1C

Yup! They have the same scale (a change of 1°C is the same as a change of 1K), so you can use them interchangeably. Just remember to keep your units consistent: if you start using celsius, stick with using celsius until you're done with the problem (same goes for Kelvin).

Naveed Zaman 1C

Well usually pumps are cylindrical, so their volume is pi(r 2 )h. We use the variable "distance" instead of "height" here, but they are technically interchangeable. Since we are depressing the pump, "d" is negative since we are reducing the volume available for gas insi...

Naveed Zaman 1C

Standard state is 1 atm pressure, and 1M concentration for solutions. The standard state for hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, and iodine is their diatomic molecular form (H 2 , N 2 , O 2 , F 2 , Cl 2 , Br 2 , and I 2 ). If you're asking for what's the standard phase of substa...

Naveed Zaman 1C

Add substance to the system, add heat to the system, or do work on the system.

Naveed Zaman 1C

You can always write out units for each of the numbers given to you if it helps. Here, we are given the mass of the substance in grams, but the heat capacities given are MOLAR heat capacities. Therefore, we have to convert grams to moles to use it with the molar heat capacity. However, you can also ...

Naveed Zaman 1C

Yup it's considered an open system because as gasoline is burned, it releases gaseous byproducts as well as heat. This indicates a transfer of both substance and heat energy, as open systems ten to do.

Naveed Zaman 1C

Yup, that's pretty much describing the first law of thermodynamics, which states that the internal energy in an isolated system will not change.

Naveed Zaman 1C

Other methods are probably better to calculate enthalpies. However, I doubt that there will be questions on the test that will give you enough info to calculate enthalpy through multiple methods in the same question. More likely is the possibility that they will ask you to calculate the bond enthalp...

Naveed Zaman 1C

I believe that and the equipartition theorem won't be on the test since Dr. Lavelle didn't cover it and it doesn't show up in the lecture outline for the chapter on his website.

Naveed Zaman 1C

R is just a constant that was derived to cancel out units to yield the unit of Joules for work. I believe the units are J/K^-1•mol^-1, which cancels out the units for n and T in the equation and leaves Joules.

Naveed Zaman 1C

This is an exception because of water's special properties. Usually, the heat capacity of solids is greater than that of liquids, so the slope for the transition from solid to liquid is more gradual/less steep than the slope for the transition from liquid to gas.

Naveed Zaman 1C

The way a thermometer works is that mercury expands when it absorbs heat. This absorption of heat is responsible for mercury rising in a thermometer under warm conditions. Since energy can still be transferred, it is considered a closed system rather than an isolated one.

Naveed Zaman 1C

Electron withdrawing power is the ability of the ion of an acid to pull the electrons that it accepts after it gives away a proton. Ions with low electron withdrawing power can't hold easily the extra electrons it accepted, so they are more likely to steal back another proton and revert back to the ...

Naveed Zaman 1C

Strong bases have weak conjugate acids, and weak bases have strong conjugate acids. A weak conjugate acid will also have a high pK a value (pK a = 10 is more acidic than pK a = 12 because you're talking about an [H + ] concentration of 1 x 10 -10 M vs. 1 x 10 -12 M). So if the pK a value is high, th...

Naveed Zaman 1C

Dipole moments are just short periods of time where electrons are concentrated on one side of the compound more than the other side. This leads to partial positive and partial negative "poles". Thus, the bigger the dipole moment, the greater the polarity of the molecule.

Naveed Zaman 1C

The "-monochloro" is just redundant. This is because whenever we don't add prefixes to a ligand it is assumed that there is only a single one present in the compound. Prefixes are only reserved for showing we have more than 1 of a ligand present in the compound (i.e. di-, tri-, tetra-, etc...

Naveed Zaman 1C

Picture a compound with 6 bonding atoms to a central atom. This forms an octahedral arrangement. You can replace any atom with an electron pair from this model because every bonding atom forms a 90° bond angle with the central atom and another bonding atom. Removing the first atom gives you a square...

Naveed Zaman 1C

Whenever you put a stress onto a system at equilibrium, the concentrations of each reactant or product will change to reestablish equilibrium (remember that equilibrium is essentially a glorified ratio of products over reactants). When you say that the reaction "equilibrium has shifted to the l...

Naveed Zaman 1C

There are certain conditions where K is a specific value that can allow you to ignore "x" because it is small, but I don't think Dr. Lavelle has taught us this and won't expect us to know it for testing purposes.

Naveed Zaman 1C

A) You want to find at what point the amount of the diatomic molecule remains constant. If you look at the 3rd and 4th flask, there is no change in the amount of each substance, so equilibrium is reached by the 3rd flask. B) 6 out of the 11 original diatomic molecules have decomposed going from the ...

Naveed Zaman 1C

Although they are involved in reactions, you don't usually measure the concentration of solids or liquid (when we have an aqueous solution of salt, we say what is the concentration of sodium and chloride ions, but we don't ask for the concentration of water). They don't really have a part to play in...

Naveed Zaman 1C

I'm not quite sure what you mean by promotion, but I'm assuming it means that the s-orbital electrons get promoted to the hybrid sp 3 orbitals. In any case, hybridization demonstrates how carbon can form 4 bonds, since the Aufbau diagram somewhat seems to show that carbon can only form 2 bonds, whic...

Naveed Zaman 1C

Ya you have the right idea. I just think of writing anion electron configurations as the same as another element with the same number of electrons. So for example, F^1- has the same electron configuration as Neon, even though they are not the same element.

Naveed Zaman 1C

Tin is a metal, so it will become a cation (since metals tend to lose electrons as ions). So it is Sn⁴⁺, not Sn^4-. Hope this helps!

Naveed Zaman 1C

The 3d subshell is higher in energy than the 4s subshell. There is actually a slight difference between energy levels 3 and 4, so that the energy in 4s is just barely below 3d. As you get to higher energy levels, the vague differences in energy also causes the 4f orbitals to begin in the 6th energy ...

Naveed Zaman 1C

Remember that the electron cloud is responsible for pretty much responsible for all of the volume of an atom. If you add electrons, you increase the volume (especially since e - to e - repulsion will increase if you introduce more electrons, causing them to space out even more). So for anions, they ...

Naveed Zaman 1C

I'm not quite sure what you mean by two dimensional graph, but wave functions (Ψ) are described in three dimensions (x, y, z). That describes where the electron could lie on a 3 dimensional graph. I've seen Dr. Lavelle use Ψ (n, l , m l ) instead of Ψ (x, y, z), which pretty much tells the same info...

Naveed Zaman 1C

The same thing happens for f-orbitals, although to a greater extent. Technically the d-orbitals are open in the 3rd energy level (which is why some elements break the octet rule in bonding), but they are not usually occupied until you have gone through the 4s orbitals. Hope this helps!

Naveed Zaman 1C

Also if you plug in a larger value for n₁ and a smaller value for n₂, you get a negative frequency value through the Rydberg equation (which we don't want). The smaller number goes for n₁ (we use n₁ to determine what wavelength series to look at - i.e. Lymann, Balmer...). Hope this helps!

Naveed Zaman 1C

The Balmer series is the set of lines formed through spectroscopy within a certain range of wavelength values. Figure 1.10 in the book shows it off better. Basically what we can take from that page in the book is that the Balmer series has the lower principal quantum number always at n 1 =2. This me...

Naveed Zaman 1C

To find wavelength, use c = λ x v (c=3x10⁸, λ is wavelength, and v is frequency). To find energy, use E = h x v (E is energy, h is Planck's constant 6.626x10^-34). You already have frequency so just plug in the value into these equations. Hope this helps!

Naveed Zaman 1C

Actually you're looking at two different laws in action. The Stefan-Boltzmann law, which relates intensity to temperature, is different from Wien's law, which relates wavelength to temperature. As you can see, we have two different equations relating different things, and so we have different values...

Naveed Zaman 1C

I believe there might be a formula that has to do with amplitude versus intensity, but I think it has to do with when we consider electromagnetic radiation as a wave, not photons. I think therefore it's something we don't have to know how to do for class purposes (I think it also has to do with only...

Naveed Zaman 1C

I believe Dr. Lavelle said that all the formula names would be provided for you on the test since we don't explicitly cover it in class, but just in case I'd review the very basic rules for naming (prefixes for ionic and molecular compounds, maybe even a couple of polyatomic ion names). But in any c...

Naveed Zaman 1C

You are partially right. What you have to realize is that they don't actually give you all the information you need. Remember that BOTH the theoretical yield and the actual yield have to be for the same thing (in this case, for CO2). What you have to do with the 42.73g of CaCO3 is use stoichiometry ...

Naveed Zaman 1C

Ya it most likely is a mistake because there is no reason that you should divide by the final mass since you are trying to compare to the initial mass. If you pretend that there is one mole of hydroxyapatite to start with, and it all turns to fluorapatite, then you would say that there is a 1.99g in...

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