CHEMISTRY COMMUNITY

Jessica Yang 1J

I think that delta U = q + w applies to all systems. It is the equation that explains the first law of thermodynamics

Jessica Yang 1J

Do we have to rate out the states of the reactants in rate laws? In the book, the states of the reactants (gas, solid, liquid) are not included in the rate laws.

Jessica Yang 1J

Hi! I'm a little confused about electrolysis. Do we put the higher reduction potential at the anode? and the lower reduction potential at the cathode? (even though the cathode will be reduced and the anode will be oxidized?) Also, if we were presented with two substances that might take place at the...

Jessica Yang 1J

Hi! For problem 15.69, I was wondering if the rate coefficient was indicative of the rate? because I notice that in the solutions manual, even though the reaction rate increase by a factor of 1000., it uses the Arrhenius Equation and comparison of rate constants instead of reaction rates to get the ...

Jessica Yang 1J

I think that the Arrhenius equation illustrates the change in k with the change in temperature because k=Ae^(Activation energy)/RT. Also I would reference equation 14 in the textbook on page 642, which compares the rate constants at different temperatures.

Jessica Yang 1J

Hi! For Chapter 15 Section 3, on page 621, there is an example for the rate law for the decomposition of ozone. In the rate law, both the concentration of products and reactants matter. How do you know when the rate law depends on both the concentration of products and reactants, and not just the re...

Jessica Yang 1J

I think it depends on the units in the rest of the problem. If it is stated that the rate is mol/L- min, then the k will probably by 1/min. However, if nothing is given in terms on units in the rest of the problem, I think it would be best to use time units as seconds.

Jessica Yang 1J

Why is the rate law only include the concentration of reactants along with k? For example, all of the rate laws in table 15.1

Thanks!

Jessica Yang 1J

I was wondering when we were calculating k, would we calculate k based on the initial concentrations and reaction rates because I remember taking notes about the importance of initial reaction rates?

Jessica Yang 1J

I think I2 is not a metal, there it does not conduct electricity. I think must conducting solids are metals or metallic.

Jessica Yang 1J

E is an intensive property so I think that E (red) will stay the same regardless. However, when approaching problems to solve for E(cell), I found this earlier post that explains it quite well, because I know Dr. Lavelle went over calculating E (cell) in two ways. https://lavelle.chem.ucla.edu/forum...

Jessica Yang 1J

Hi I am confused with how we are supposed to calculate K at pH= 1 and pH= 14. In the solutions manual, it states that the K at pH=14 is (1.0 x 10^-14) / (1.0). Where did we get the 1.0 M from? Also for the pH=1 the K is (0.1/ 1.0 x 10^-14). Where did the 1.0 x 10^-14 come from?

Jessica Yang 1J

How come the I- (aq) is written in the innermost to the salt bridge, when it is the reactants part of the reaction with Ag(s) to make AgI (s) + e- ?

Jessica Yang 1J

I would think of it as one being less negative than the other. Since the -3 is more negative than the -1, the -1 needs to have two electrons added to it for it get the charge of -3. In order words the I- is reduced to I3-.

Jessica Yang 1J

Hi!

Why do we use platinum for the iodide solid because i thought we if we were dealing with solids there would be no use for an inert electrode?

Jessica Yang 1J

Hi! I know that in the solutions manual to assume 1.00 moles of nitrogen gas for this problem, but could we have hypothetically calculated the moles of nitrogen gas given that it is an ideal gas with PV = nRT?

Thanks

Jessica Yang 1J

For a free expansion process, is the change in internal energy 0? Also it if it is, can you explain why? and how free expansion is supposed to have positive entropy?

Jessica Yang 1J

I think it is because E is an intensive property, meaning that does not depend on the system size or the amount of material in the system

Jessica Yang 1J

Also since oxidation means loss of electrons, oxidation occurs in the anode side of the cell because it is the supplier of electrons (e-) to the other side of the cell.

Jessica Yang 1J

For the equilibrium constant when calculating gibbs free energy of change in G=-RTlnK, can K only be calculated in terms of pressure for moles of gas or can it also be calculated with the concentrations of the the moles of gas? I remember distinctly that K can only apply to partial pressures and tha...

Jessica Yang 1J

Hi I am still a bit confused on reversible processes and what they mean. I know that they are slow in process, but while measuring entropy in reversible processes if one factor was not constant, like when we calculate change in entropy of temperature, pressure, or volume, does that mean the remainin...

Jessica Yang 1J

I think that change in internal energy is 0 because it says that the reaction is isothermal. I remember that internal energy is dependent on the temperature of the system for an ideal gas so if the temperature is constant, then no heat is moving in or out of the system, and the change in internal en...

Jessica Yang 1J

Residual molar entropy is the entropy that still exists due to positional disorder at T=0, because at T=0, there should hypothetically be no entropy if the molecule is a crystal, as seen by the third law of thermodynamics. I drew the different orientations of SO2F2, with S being the central atom bec...

Jessica Yang 1J

For when we write out combustion equations and calculate enthalpy of combustion, do we treat the water in the products as a water or gas? (because I think the enthalpy of formation of water as a gas and water as a liquid is different)

Jessica Yang 1J

I think that they did not include it because the enthalpy of formation for N2 gas is 0 and it does not contribute to the enthalpy formation.

Jessica Yang 1J

I know that the equation is change in enthalpy = change in internal energy - work, but can someone conceptually explain why when work is done by the system (therefore, volume expands) why enthalpy is greater than internal energy? and vice versa for when work is done on the system?

Thanks!

Jessica Yang 1J

For the problems, you have to convert the reactants from gas to liquid phase. When you convert from gas to liquid phase, is enthalpy positive or negative and why?

Jessica Yang 1J

Heat Capacity is more generalized and it doesn't matter about the mass of the substance. It is equal to heat supplied/ temperature rise produced. For example, it takes 12 Joules to raise the temperature of water by 2 K. Therefore, the heat capacity of this water is 6 Joules/K. Specific Heat capacity...

Jessica Yang 1J

Hi. I think we use PV=nRT in this chapter to calculate enthalpy. In the example in class today, it says that change in enthalpy = change in internal energy + P (change in V). If we do not know the change in volume of the system and it is not given, we can use the change in moles of gas to calculate ...

Jessica Yang 1J

If there is no change in the moles of gas, there will be relatively little expansion work done and little heat lost as work, which would result in change in enthalpy to equal change in internal energy. If there is a net change in the moles of gas, there will be expansion work done and the system wil...

Jessica Yang 1J

Hi! An open system is where both matter and energy can be exchanged with the surroundings. A closed system is where only energy can exchanged with its surroundings (i.e. heat) because the closed system cannot get any more matter (number of moles does not change). An example would be a cold pack (I'm...

Jessica Yang 1J

I don't think we will have to because those are the only ones I see in the book, but if Dr. Lavelle mentions any other types of calorimeters, I think we will be expected to know them

Jessica Yang 1J

While the ice cube is gaining heat from the water, the water is simultaneously losing the same amount of heat. The negative sign indicates the loss of heat

Jessica Yang 1J

Do ionic bonds (with larger electronegativity difference) tend to have a lower or higher disassociation energy compared to covalent bonds?

Jessica Yang 1J

Once you determine the K of both dissociations by using the ICE table, you figure out that the K of chlorine is smaller than the K of fluorine. As a result, you know that in dissociation equilibrium, chlorine favors its reactants more (since K = concentration of products/concentration of reactants) ...

Jessica Yang 1J

What I think the book was trying to do was hydronium ion H30+ and hydroxide ion OH- and that would equal 2H20 I think I remember in class that Dr. Lavelle sometimes said that hydronium was abbreviated to H+.

Jessica Yang 1J

For 17.29d, why did the book place the sulfate ligand (S04)2- before the anime (NH3) ligand? I thought that the ligands were supposed to be placed in alphabetical order in the molecular formula as well.

Jessica Yang 1J

The complex, which doesn't include the potassium is still negative. The 6 F's create a -6 charge and the Co creates a +3 charge, resulting in an overall -3 charge for the complex. The entire coordination compound, which includes the potassium, is of neutral charge.

Jessica Yang 1J

I thought we named ligands in alphabetical order, so why did the book list bisoxalato before the diaqua in problem 17.31d? I know we are also supposed to disregard the prefixes when putting the ligands in alphabetical order as well.

Jessica Yang 1J

It would be bent around the O atom because there are four regions of electron density, but two of the regions are occupied with lone pairs. This shape can also be seen in the common example of the O atom in water, which is also bent and has four regions of electron density: two are lone pairs and tw...

Jessica Yang 1J

I know that in class Dr.Lavelle said that one pi bond means that the atoms are forced in place and any rotation would result in a breaking of the pi bonds. What would happen with two bi ponds? Someone mentioned that they could rotate but I don't understand how.

Jessica Yang 1J

I think that you can treat the the C-Cl dipole bonds are vectors. That way in 3, the dipole moments cancel each other out, because they have the same magnitude but are pointing in different directions. The C-Cl dipole bonds in 2 (120 degrees) have less overlap than those in 1 (60 degrees). I think t...

Jessica Yang 1J

I also think that the closer together similar charges are, the more of a dipole moment there is. And for 1 on 4.29, I think it has the biggest dipole moment also because of the smaller angle between the two C-Cl bonds

Jessica Yang 1J

Hi I was wondering how to distinguish between a tetrahedral and a trigonal pyramid. I know both have four electron densities. Also how would hybridization would work differently for the two structures?

Jessica Yang 1J

It is from chapter 4

Jessica Yang 1J

Hello,

I am confused about resonance structures and delocalized electrons. What is a delocalized electron and could you provide an example with the specific delocalized electrons marked or highlighted in some way?

Jessica Yang 1J

Hi

For Ga+3, the neutral state configuration is [Ar]3d10 4s2 4p1. I think the issue was that you forgot that once the 3d orbitals start filling up with electrons, it becomes lower in energy than the 4s orbital. Therefore, you take the 4s2 and 4p1 out.

Jessica Yang 1J

Hi!

I'm a bit confused about effective nuclear charge and the trends in the periodic table regarding the effective nuclear charge, and shielding. How does the effective nuclear charge relate to (if it relates to) shielding?

Jessica Yang 1J

Hi!

Resonance structures only differ in structure of electrons. However, isomers differ in structure of electrons and atoms. They are essentially different compounds with the same number of atoms. Examples of isomers include butane and isobutane that you can look up on google if you want

Jessica Yang 1J

Regarding the carbon question, an uncharged carbon atom will have 6 electrons. 2 go in the 1s orbital (paired), 2 go in the 2s orbital (paired), and the other 2 will go in the 2 p orbital. One will be in the p sub x and one will be in the p sub y. They are unpaired because they first need to fill th...

Jessica Yang 1J

I think the Heisenberg indeterminacy equation is used to show that the exact momentum ( and thus velocity) and the position of an electron in an atom cannot be known. The indeterminacy of momentum x the indeterminacy of position has to be greater than h/4pi. If there is a greater indeterminacy in mo...

Jessica Yang 1J

Both the Balmer and Lyman series work only for hydrogen. In the Balmer series, the electron transitions from higher energy levels to n=2 and for the Lyman series, the electron transitions from higher energy level to n=1

Jessica Yang 1J

I don't think we need to know the exact conversion, because all of the conversions will probably be given to us on the equations sheet. However, it would be helpful to know how to convert from kEV to Joules as general practice.

Jessica Yang 1J

I think it would be sufficient enough to just find the limiting reactant and then follow by finding the theoretical yield. I think the book just went an extra step.

Jessica Yang 1J

I agree. I don't start rounding off my sig figs until the very end when I receive the answer, to which I then correctly round the sig figs to. However, I am sure that even if you round your sig figs after every step, points will not be taken off for not having the most accurate answer.

Search found 55 matches