CHEMISTRY COMMUNITY

Kevin Ru 1D

A galvanic cell (left) transforms the energy released by a spontaneous redox reaction into electrical energy that can be used to perform work. In an electrolytic cell (right), an external source of electrical energy is converted to chemical energy.

Kevin Ru 1D

I believe it applies to just isothermal reactions.

Kevin Ru 1D

Could you the post the question as I think there are different test versions?

Kevin Ru 1D

The question is: A piston containing 0.10 mol of nitrogen gas at 298 K has an initial volume of 2.24 L and undergoes an expansion against 0.5 atm external pressure until its volume doubles. Calculate the work involved in Joules. The key here is that it states there is an external pressure of 0.5 atm...

Kevin Ru 1D

I believe that molar mass would still be considered an intensive property. Since it is still the mass of one mole of a given substance and thus does not depend on the amount of substance.

Kevin Ru 1D

Internal energy is due to motion of particles in a system which depends on temperature. As you mentioned, temperature in isothermal process is constant, so the internal energy will also be constant. Therefore, the change in internal energy 0. Hope that helps!

Kevin Ru 1D

While Dr. Lavelle has said that he wouldn't directly ask us to derive equations in the past, it would be a good idea to know how to derive the order of reaction equations.

Kevin Ru 1D

As the above poster mentioned, all assigned homework questions are fair game. In terms of finding posts by TAs/UAs, I would try using the search user function and search for "Chem Mod"

Kevin Ru 1D

I think that there is possibility that we will be asked to derive on not just the final, but the quiz as well.

Kevin Ru 1D

To find the moles of electrons transferred, you'll want to look at the two balanced half reactions and make sure that the electron change is same in both.

Kevin Ru 1D

I believe the two half reduction reactions were found in Appendix 2B.

Kevin Ru 1D

You have to look at how many electrons are transferred in the balanced half-reactions. In other words, find the number of electrons in each balanced half-reaction. If they match, that is n. If they don't match, take the lowest common multiple, and that is n.

Kevin Ru 1D

If Q is greater than K, the reaction will shift to the left and if it's less than K then the reaction will shift to the right!

Kevin Ru 1D

Yes. Generally speaking, the left side of the cell diagram will correspond to the anode (oxidation) while the right side will correspond to the cathode (reduction). Hope that helps!

Kevin Ru 1D

The two actually refer to the same type of electrochemical cell. That is that they both convert chemical energy into electrical energy. Hope that helps!

Kevin Ru 1D

Another way to remember this is OIL RIG. Oxidation is Loss. Reduction is Gain. So you'll want to compare the reactants and products and see if the oxidation number decreases or increases to help determine whether or not it was oxidized or reduced.

Kevin Ru 1D

Both! For example, a common material for salt bridges is KCl. The K+ ions dissociate into the cation end, and the Cl- ions dissociate into the anion end to counter charge buildup.

Kevin Ru 1D

Are you referring to delta u in an isothermal reaction? This is because for an ideal gas U = 3/2 nRT. Therefore, if the moles of gas stay the same, n is constant, R is the gas constant, and if T is constant (which is what isothermal means) then U is constant which means delta U = 0.

Kevin Ru 1D

You might be getting confused with the entire universe vs the "observable" universe. The entire universe is isolated because it contains everything by definition, and has no surroundings as a result. It literally is everything. However, if you are referring to the universe that we can see,...

Kevin Ru 1D

Just adding onto the above post. The first equation is looking at when the change in volume is positive; therefore entropy is increasing. The second one occurs under constant pressure and we are looking at the change in temperature. Here, lower temperature means higher entropy. Hope that helps!

Kevin Ru 1D

You should convert to Kelvin as it is no longer ΔT in the equation, but T (The general formula for change in entropy being ΔS = qrev/T).

Kevin Ru 1D

I believe the answer to your question is yes. Entropy is still increased because of the kinetic energy being given off as heat, so while the entropy is low in terms of less positions/dispersed, the total entropy is higher because of the change in temperature. Hope that helps!

Kevin Ru 1D

Dr. Lavelle has been making a point to avoid using the word "disorder" when discussing entropy, so I believe avoiding that terminology might help with understanding it. Based on the two principles mentioned above, a system is stable when the internal energy is at its minimum and the entrop...

Kevin Ru 1D

Generally this should be true for all endothermic processes as raising the temperature of the reaction favors the products. This means that the reverse reaction is favored which is exothermic. Hope that helps!

Kevin Ru 1D

An extensive property depends on the amount of matter in a sample (Ex: Volume). In contrast, an intensive property is independent of the amount of matter in a sample (Ex: Density). Hope that helps!

Kevin Ru 1D

Just to add on that R represents the gas constant which varies depending on what units you are using. As mentioned above, it can be found on the constant and equations sheet on Dr. Lavelle's website.

Kevin Ru 1D

I believe we are assuming the reaction takes place at room temperature (25 ºC/298 K).

Kevin Ru 1D

One way that I think of to remember it is that INtensive properties are INdependent of mass. Meanwhile, an EXtensive property will increase if an EXtra amount is added as it does depend on mass. Hope that helps!

Kevin Ru 1D

A calorimeter is how we measure specific heat capacity. The coffee cup calorimeter measures heat under conditions of constant pressure while the bomb calorimeter measures heat under constant volume. Not sure about your second question, but I do suspect that we'll see more of it in problems and appli...

Kevin Ru 1D

Hess's Law can be defined as: The overall reaction enthalpy is the sum of the reaction enthalpies of the steps into which the reaction can be divided. In that example, we're looking at two steps of the reaction, Nitrogen oxide formation (N2 + O2 --> 2NO) and then its reaction with oxygen (2NO + O2 -...

Kevin Ru 1D

As you know, Heisenberg's uncertainty principle is: Δp x Δx ≥ h/4π Now, the question gives us the mass of the marble as well as the uncertainty in velocity which allows us to find Δp. Since momentum is mass x velocity, you take 1.5 x 10^-3 kg (converted from grams) x 1.1 m/s (because +/-). This will...

Kevin Ru 1D

Mg will actually have a smaller second ionization energy than Na because the first ionization energy of Na results in Na+ having a full valence shell (similar to Ne). As having a full valence shell is very favorable, it will be more difficult to remove a second electron from Na in comparison to Mg (...

Kevin Ru 1D

Yes, lone pairs also contribute to the type of hybridization. For example, BrF3 has a Br with two lone pairs bonded to three F atoms making it sp^3d (5 areas of electron density). Hope that helps!

Kevin Ru 1D

What makes a strong acid completely ionize or disassociate as opposed to a weak one? Strong acids have mostly ions in solution, therefore the bonds holding H and A together must be weak. In other words, strong acids easily break apart into ions allowing them to completely dissociate in contrast to ...

Kevin Ru 1D

The pH of a solution is related to its concentration of hydrogen ions - the higher the concentration of hydrogen ions H+ the lower the pH. At the same concentration of acid, the concentration of hydrogen ions will be higher in a strong acid than in a weak acid. This is because a strong acid will don...

Kevin Ru 1D

Solids and liquids are not included in the K expression because their concentrations stay constant throughout the reaction. Therefore, they do not affect the reactant amount at equilibrium in the reaction. Hope that helps!

Kevin Ru 1D

Even though there is no net change at equilibrium, both the forward and reverse reactions are still taking place. In other words the reactants are being formed as fast as they are consumed. Hope that helps!

Kevin Ru 1D

It is a pentagonal bipyramidal because there are 7 bonding electron pairs with 0 lone pairs. Hope that helps!

Kevin Ru 1D

To clarify the above post. Isoelectronic atoms or ions have both the same number of valence electrons (8 in this case for F-) and the same electronic structure. As [He] only has 2 valence electrons it cannot be isoelectronic to F-. Hope that helps!

Kevin Ru 1D

Remember that atoms or ions are considered isoelectronic only when they have both the same number of valence electrons and the same electronic structure. Hope that helps!

Kevin Ru 1D

Hi, I don't believe there is a way for us to determine the magnetic quantum number (ml) a specific electron has without doing an experiment. Thus, we will most likely not be asked about a specific ml number. Rather it is more likely that we will be asked about the range such as on the previous quiz....

Kevin Ru 1D

Hi! The formula for finding formal charge is actually Valence Electrons - (Lone Pair Electrons + Shared Electrons/2). Hope that helps!

Kevin Ru 1D

Hi there, multiple bonds (such as a double bond) are shorter than single bonds between the same two elements because the additional bonding electrons attract the nuclei more strongly and pull the atoms closer together. Hope that helps!

Kevin Ru 1D

I believe that this refers to the proximity of the electrons in an orbital to the nucleus. Therefore when it says "the s orbital penetrate the nucleus" they are saying how close the electrons in the s orbital are to the nucleus. The textbook then goes on to say that p orbital "penetra...

Kevin Ru 1D

Hi! The reason why the nodal planes are different once you reach the d orbital is because there are more orbitals. While p has 3 orbitals, d has 5 orbitals of a given energy.

Kevin Ru 1D

Hi, yes there are different nodal planes for these orbitals as well. D orbitals have 5 while F orbitals have 7. I believe that Dr. Lavelle said during lecture that we won't be going over F orbitals, so I'll just list the D orbitals. dxy, dyz, dxz, dz^2, and dx^2y^2. Hope this helps!

Kevin Ru 1D

In terms of relevance, I believe that experiments involving black bodies eventually led to the Quantum theory as experiment results could not be explained by classical mechanics. This issue wasn't solved until Planck came along and suggested that the exchange of energy occurs in quanta (packets) of ...

Kevin Ru 1D

In Wien's law, lambda is still used to represent wavelength. Lambda max refers to the wavelength in the absorption spectrum where the absorbance is maximum. In other words, lambda max is the wavelength that corresponds to the maximum in the intensity which is where you might have gotten confused. Ho...

Kevin Ru 1D

I believe the M is indeed a variable that represents the unknown metal in the compound. Since you can calculate the molar mass of (OH)2, you can then subtract that from the given molar mass of the compound to find out the molar mass of "M". After checking the periodic table you will discov...

Kevin Ru 1D

Theoretical yield is what you calculate with Stoichiometry and is the maximum amount of product that can be produced. The percent yield is the fraction of the theoretical yield that is actually produced aka the amount of the theoretical yield that you obtained, expressed as a percentage. You would f...

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