CHEMISTRY COMMUNITY

Alexander Vong 3I

There might be an error. You're right; you should calculate the q needed to raise the temperature to 100oC, the energy needed to vaporize, and the energy released when its cooled back to 25oC. You would only do this when carrying out an entropy of vaporization calculation at a temperature other tha...

Alexander Vong 3I

To add, the "parent" may not always be a single chain. The parent can be a cycloalkane, cycloalkene, or cycloalkyne if the cyclic chain contains more carbons than the substitutents. For example, a ring with 6 carbons will be called the substituent if it is attached to a propyl. The propyl ...

Alexander Vong 3I

To add, I find it more intuitive to set r, or R, to 8.314 J/K mol and keep x as 125 x 10³ J/mol

Of course, the approach described above works too

Alexander Vong 3I

In problem 15.63, the units for the rate constant are L/mol-s. The problem asks to solve for the rate constant at another temperature, given the activation energy.

However, the answer in the back of the book has the units mol/L-s

Why are the units different?

Thank you!

Alexander Vong 3I

One important thing:

Note that the problem gives the temperatures in Celsius, so you would have to convert them to Kelvin.

Alexander Vong 3I

Yes, anything that is not an intermediate contributes to the order. Intermediates do not show up in the overall reaction.

Alexander Vong 3I

To add, the time it takes for the concentration to halve is also not co start in a zero order reaction.

Alexander Vong 3I

Also, catalysts lower the activation energy so the reaction happens more easily.

Alexander Vong 3I

The rate constant in a second order reaction would be
the slope of the
line of the inverse of the concentration of reactant plotted against time.

Alexander Vong 3I

Ni is the cathode because it's reduction reaction has a more positive standard reduction potential than SO 4 2- We don't need to change the sign because it is already accounted for when we subtract the cathode potential from the anode potential. If we were to change +1.23V to -1.23V, then we would a...

Alexander Vong 3I

Does aeration of a solution mean that oxygen is actually reduced in redox?

I infer that apparently it does, since the solutions manual includes the reduction of water and oxygen gas.

Can someone please validate this?

Alexander Vong 3I

An anode reduction potential in itself is not negative. However, when we calculate the the difference potential of the cell, we subtract the potential of the cathode from the potential of the anode. If we need to balance equations ( in terms of charge), then we flip the sign of the reduction potenti...

Alexander Vong 3I

SubparChemist wrote:
The final answer multiplies both the reduction and oxidation reactions by two, just to eliminate the fraction in the .5H2(g)->H^+ + 1e-

The half-reaction would actually be H₂(g) --> 2H⁺(aq) + 2e^-

Alexander Vong 3I

OH- is placed to the left of the Oxygens because it represents the solution that is connected to the salt bridge.

Alexander Vong 3I

Actually, it is, in fact, an error. It should be e-, not 2e-.

Chem_Mod verified this.

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=140&t=11410

Alexander Vong 3I

We calculate the standard Gibbs free energy by adding the standard Gibbs free energies of the
two half reactions,
Tl--> Tl³⁺ + 3e^-
and
Tl⁺ + e^- --> Tl

Alexander Vong 3I

Apparently there are 2 electrons transfered per mol in a Daniell cell. Considering that the battery uses copper and zinc, it would make sense that 2 electrons are transfered, since the reduction half-reaction of Zinc involves the transfer of two electrons, while the half-reaction of copper could inv...

Alexander Vong 3I

Platinum is an inert conductor, which basically means it can be used to conduct electricity complete a circuit. The electrons can flow through it. We add inert conductors such as platinum to the design of a battery when there are no conducting electrodes that we can get from the redox equation. Some...

Alexander Vong 3I

Yes, you are right. Use inert conductors such as platinum if there are no conducting metals already in the electrode.

Alexander Vong 3I

For the use of H20, you can use OH and H in problems involving acidic solutions.

Alexander Vong 3I

The oxidation number of an atom is derived from the bonds it makes from other atoms. An atom's charge is influenced by differences in electronegativity. For example, every C-H bond will decrease the oxidation state by 1, and every carbon bond to a more electronegative element will increase the oxida...

Alexander Vong 3I

Reduction potential is an intensive property, so it does not depend on quantity.

Alexander Vong 3I

Learning about equilibrium is easy...

...because nothing changes

Alexander Vong 3I

How would one calculate residual entropy, or is residual entropy something that will always be given?

Alexander Vong 3I

Would it be 6^10x23, or is that for a different equation?

Alexander Vong 3I

By enthalpy do you mean the enthalpy of formation? The enthalpy of formation of an element in its standard state is zero, but the enthalpy of vaporization fo a substance is not zero.

Alexander Vong 3I

Work is positive in step 2 because upon returning to the original internal energy, some of the decrease in the internal energy done in step 1 is undone.

Alexander Vong 3I

This reaction is taking place presumably at standard temperature and pressure, so the pressure is 1 atm and the temperature is 0 degrees Celsius. Assuming the gas has ideal behavior, we can use PV= nRT to find the moles of gas. The pressure is at 1 atm, and the problem provides the volume, You can u...

Alexander Vong 3I

When a substance is in the gas phase, it is more disordered. An increase in entropy favors gases, as with more entropy comes more disorder.

When a substance is below the boiling point, entropy wants to decrease.

Alexander Vong 3I

Yes, the R's related to heat capacity and work are all equivalent. You choose which one to use based off of which units you need to accommodate.

Alexander Vong 3I

Do we use the same equation, $\Delta S = -nRln\binom{Vf}{Vi}$ for both isothermal expansions and compressions? If so, what is the conceptual reasoning behind it?

Alexander Vong 3I

Are you referring to an increase in entropy of a particular system? An increase compared to current fuels (if so, which fuels)? An increase in entropy is an increase in the number of particles and/or kinetic energy. Biodiesel fuels have a high enthalpy density, while methane has a low enthalpy densi...

Alexander Vong 3I

Processes involving constant temperature are also known as isothermal processes. Isothermal processes can mean that heat is put into a system. However, there is no change in internal energy because all of the heat energy is used to do work. Recall the Pressure vs. Volume graph. To calculate the work...

Alexander Vong 3I

Is this in the purple workbook for Winter 2016?

Alexander Vong 3I

If the actual entropy is close to the second entropy (the experimental value), it helps us find out how molecules are arranged in a solid. The purpose of the Boltzmann formula is to show that the orientations a molecule can have is related to its entropy. It appears, from looking at example 9.8, tha...

Alexander Vong 3I

Free energy is energy available to do work.

Alexander Vong 3I

Keep in mind, heat transfer can change entropy. If heat leaves a system, the entropy decreases. Considering that the entropy of the universe is zero, somewhere else there has to be an entropy change that is positive to balance out the first entropy change.

Alexander Vong 3I

Entropy, being a measure of disorder, can change when the reactant undergoes a phase change. If the reactant changes from a gas to a liquid, the entropy decreases, because a substance is more disordered as a gas than as its liquid.

Alexander Vong 3I

If you're measuring change in internal energy based off of q when heating a system under constant volume, you would use q=nC_vdelta T

Here, if delta T is zero, q is zero and the change in internal energy is zero.

Alexander Vong 3I

Here's a hypothetical example: A system, defined as a metal pot, is heated with a stove that has an output of 100 joules per second. The pot is heated for 5 seconds. While the pot is heated, it turns out that the pot (the system ) underwent a change in internal energy of +1000 joules. Calculate the ...

Alexander Vong 3I

But how do you know what the sign of the forward reaction was to begin with? is that dependent on whether the reaction is endothermic or exothermic? Yes, an enthalpy value for a reaction depends on whether it's endo- or exo- thermic. For example, consider the reaction of methane with water vapor. C...

Alexander Vong 3I

In question 13.35, part f) asks to find the pH at the stoichiometric point. In this exercise, CH 3 COOH is the weak acid with a molarity of 0.1. It's titrated with 0.1 M NaOH. Here the solutions manual, when solving for pH at the equilibrium point, sets the molarity of CH 3 CO 2 - as 0.05 M. Why is ...

Alexander Vong 3I

What is the maximum number of electrons in an atom that can these quantum numbers? n=2 m1=1 ms=+1/2 Let's consider that energy level (N) equals 2. Therefore, L can equal 0 and 1. L=0 represents the s-orbital. L=1 represents the p-orbital. For the s-orbital, an electron can have 1 orientation, since...

Alexander Vong 3I

The dissociation of HCL is not a reversible reaction. Therefore, an equilibrium sign may not be appropriate. In theory, an equilibrium sign would be appropriate only if: You have a flask containing HCL and water. HCL was dissociating into H+ and Cl- at a certain rate. Somehow, H+ and Cl- were formin...

Alexander Vong 3I

Additionally, the Cl would not be able to fit in, as the S would have a full octet.

But wait...S can break the octet rule...

Alexander Vong 3I

But how exactly do we find the final volume ( which is after the stoichiometric point)? The stoichiometric point is when the pH is 7 and the total volume is 10ml, but this is not the final point. Theoretically, more HCL would be added so that the [HCL] = [NaOH], but is there a way to find how much e...

Alexander Vong 3I

Would we be required to find the final volume? In this case, is finding the final volume even possible?

Alexander Vong 3I

Alexander Vong
504598309
Discussion 1D

I hope this is helpful!

Alexander_Vong_Chem_14A _1D.mp4 [ 418.65 MiB | Viewed 607 times ]

Alexander Vong 3I

Say a ligand were to consist of a cation and multiple oxygens. If there were oxygens with 2 lone pairs but also oxygens atoms with 3 lone pairs, which oxygen atom would be used for determining the number of coordinate bonds made?

Alexander Vong 3I

Say an atom is surrounded by 6 areas of electron density, and therefore the hybridization is sp³d². Would the d² part be written before sp³ or after?

Alexander Vong 3I

The term "main group metal" appears on p. 66 of the course reader. To quote: " Main group metal forms cation: loses s and p valence e- (e- configuration of preceding inert-gas atom). p-block element forms anion: gains e- until following noble-gas e- configuration is reached " Do ...

Alexander Vong 3I

The abbreviation, "-VE", appears in the course reader several times. Could someone please clarify the meaning of VE? It appears in the following context: (on p.75) An e- pair in a covalent bond may not be equally shared [between two atoms] The atom with the closer e- pair is slightly -VE( ...

Alexander Vong 3I

When n=2, and a s orbital and 2 p orbitals are hybridized, is 2sp² a shell or an orbital?

Alexander Vong 3I

In the work function equation, can Energy emitted be negative?

Alexander Vong 3I

Is it more important on say, a quiz, to know how to write an entire electron configuration without using noble gases to denote non-valence electrons, or are we allowed to write just the noble gas core and then the valence electrons? For example, consider calcium. Would it be important to know how to...

Alexander Vong 3I

Exercise 1.43 from Chapter 1 asks, "What is the minimum uncertainty in the speed of an electron confined to within a lead atom of diameter 350. pm? Model the atom as a one-dimensional box with a length equal to the diameter of the actual atom." Could someone please clarify what "model...

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