CHEMISTRY COMMUNITY

Karen Ung 2H

According to my TA, information on whether the steps in a mechanism are slow or fast will be given.

Karen Ung 2H

Normally, if there are more elements or number of elements in a molecule, that has greater residual entropy, but generally, bigger molecules have greater residual entropy in which case you calculate the molar masses of each molecule to find which one is bigger.

Karen Ung 2H

I may have had a different test from you nurmerically, but I'm pretty sure in 6D you're able to add the standard potentials because they're from the half reactions. So, based of the equation E(anode)+E(cathode) = E cell, you get the overall standard cell potential. On #7, you can't do the same thing...

Karen Ung 2H

I had trouble identiying the elements in the half reactions as well, but as a quick solution, I think it's best to refer to the table of half reactions since this is a more complicated reaction. The half reactions will most likely be given on the final since they were also given on the tests. Hope t...

Karen Ung 2H

Reaction: Ce4+(aq) + I-(aq) -> I2(s) + Ce3+(aq) I separated into half reactions, identified the reduction and oxidation reaction, and write the cell diagram to be: I2(s) | I-(aq) || Ce3+(aq), Ce4+(aq) | Pt(s) But, the correct cell diagram is Pt(s) | I2(s) | I-(aq) || Ce3+(aq), Ce4+(aq) | Pt(s) Why i...

Karen Ung 2H

I got that answer too. I believe it is fine to round the number to 9.

Karen Ung 2H

I'm not sure how to get the answer in the solutions. The correct answer is supposed to be 2.85x10^(12). I keep getting k=2.85 by inputting the values of experiment 1 into the rate law.
Rate law: rate = k[A][B]^(2)[C]^)2)
8.7 = k (1.25)(1.25)^(2)(1.25)^(2) -> k = 2.85

Karen Ung 2H

There are two types of rate laws. One of them is the differntial rate law, and the other is the integrated rate law. The differential rate law depends on the concentration and describes the reactions rate in terms of (delta) [R] / (delta) t. The integrated rate law is the integration of the differen...

Karen Ung 2H

You can use H+ to balance the number of H's. I think using the H3O+ is the correct way to balance corresponding to the reaction, but my TA brought up in section that you can use H+ and then replace it with H3O+ at the end since it makes more sense to use H+ when balancing.

Karen Ung 2H

Why does the left side of the cell diagram not have a Pt(s), and the right side does?

This is the reaction: 2(NO3)-(aq) + 8H+(aq) + 6Hg(l) -> 3(Hg2)2+(aq) + 2NO(g) + 4H2O(l)

Karen Ung 2H

I'm also confused. Why can you assume that you there is a Ag cathode and Br anode?

Karen Ung 2H

The cathode is usually identified as an oxidation reaction, and the anode is identified as a reduction reaction. I believe the signs for the values of the cell potential of the cathode/anode are flipped if you filpped the equation, and vice versa.

Karen Ung 2H

You would reverse it if you were using the equation Ecell = E(anode) + E(cathode). There's another equation Ecell = E(cathode) - E(anode), where you don't need to flip the sign.

Karen Ung 2H

Additoinally, there are a few rules you can follow when determining oxidation states. H will always have the oxidation state of +1. O will have the oxidation state of -2, except in H2O2, when oxygen's oxidation state is -1. The charges of elements are the oxidation state numbers. For example, Cr 3+ ...

Karen Ung 2H

How do you know when to use Pt as an anode/cathode?

Karen Ung 2H

Write the half-reaction, the balanced equation for the cell reaction, and the cell diagram for the following skeletal equations: c) Cl2(g) + H2(g) -> HCl(aq) I don't understand why it doesn't split into the two half reactions: 1) Cl2 -> HCl 2) H2 -> HCl Also, an explanation would help. Thanks!

Karen Ung 2H

True or false: Removing heat from a system is exothermic, so temperature must decrease. If energy is being removed from a system, isn't it similar to an exothermic process, which means the temperature of the system should decrease? Why is the answer false?

Karen Ung 2H

Does delta S of the total reaction = 0 when a process if reversible? Why?

Karen Ung 2H

The bigger the molecule, the higher the molar entropy. When determining the greater molar entropy, does disorder in the number of different orientations matter more than the size of the molecule?

Karen Ung 2H

Why does W = 6 raised to avogadro's number? I don't get avogadro's number part. Can't it be 6 (# of orientations) raised to 6 (# of different molecules)?

Karen Ung 2H

For an adiabatic system, q=0, but that does not mean necessarily mean that temperature = 0.

Karen Ung 2H

Why can you assume that n=1.00mol? Is it because of the ideal gas laws? Can it be further explained if it is?

Karen Ung 2H

I believe this is an error in the solutions manual. The correct solutions uses Cv. Here's the link: https://lavelle.chem.ucla.edu/wp-conten ... rs_6Ed.pdf

Karen Ung 2H

In addition to the above responses, it is important to note that a bomb calorimeter is at constant volume, which means work = 0.

Karen Ung 2H

When you add more of an amount of a substance in a system, does it increase or descreae the energy of a system?

Karen Ung 2H

Do we have to add the heat of the calorimeter with the heat of the reaction to calculate the amount of heat released/absorbed from the reaction? Or is the heat absorbed by the calorimeter negligible?

Karen Ung 2H

Estimate the enthalpy of the reaction between bromine and propene (propylene) to form 1,2-dibromopropane. The enthalpy of vaporization of Br2 is 29.96 kJ/mol, and taht of CH3CHBrCH2Br is 35.61 kJ/mol. The reaction is Br2(l) + CH3CHCH2 -> CH3CHBrCH2Br(l). In order to solve the problem, I tried a diff...

Karen Ung 2H

Diatomic molecules are made of two elements. The seven diatomic elements from the periodic table are nitrogen, oxygen, bromine, iodine, chlorine, hydrogen, and fluorine. Because they are the same elements, they have a standard enthalpy change of 0.

Karen Ung 2H

What's the difference between an isothermal system, an isothermal system with an ideal gas, and an adiabatic system?

Karen Ung 2H

An adiabatic system only allows the transfer between one energy: work. In this case, q = 0, but this does not necessarily mean the change in temperature (or delta T) is equal to 0 since the internal energy may also change when work occurs within the system.

Karen Ung 2H

Cv, m = 3/2R is the equation used to calculate a heat capacity for atoms or monotomic atoms at a constant volume. Cp, m = 5/2R is the equation used to calculate a heat capacity for atoms at a constant pressure. The R represents the gas constant, R = 8.314 J/K*mol.

Karen Ung 2H

The book states that the heat capacity of a dilute solution is taken to be the same as the pure solvent. Why?

Karen Ung 2H

How do you know when the dipole moments of some molecules can cancel out?

Karen Ung 2H

Strong acids and bases do not have Ka and Kb values because they completely dissociate in water. Ka and Ka are used to describe only weak acids, but pH values can be used to describe both strong and weak acids.

Karen Ung 2H

Lone pairs are taken into consideration when naming the shape of the molecule because the electron repulsion from the lone pairs affects the bond angles and therefore the shape of the molecule.

Karen Ung 2H

I believe that if you wanted to write the ligands in alphabetical order, you'd refer to the name (amino) rather than the molecule (NH3). In addition, it's helpful to note that prefixes are not taken into consideration when alphabetizing.

Karen Ung 2H

Normally, the Roman numerals are written after the name of the compounds between the brackets so that you can specify the charge of the transition metal.

Karen Ung 2H

To tell the hybridization, I usually look at the number of electron dense areas. The total number will help you identify the hybridization by looking at the exponents of each letter. For example, an atom with four electron dene areas will have a hybridzation of sp^3.

Karen Ung 2H

Angular is synonymous to bent. You can use either angular or bent to describe a certain molecular structure.

Karen Ung 2H

Normally, I'd draw the bonds to connect the atoms together first and then figure out how many electrons are left to distribute amongst the structure. It's helpful to know how the formal charge equation plays a role in each atom when assigning bonds. For example, oxygen has six valence electrons, so ...

Karen Ung 2H

For Lewis structures, the atom with the lowest ionization energy will be used as the central atom. Additionally, carbon, when present, is usually the central atom.

Karen Ung 2H

As an exception for the electron affinity periodic trend, why does nitrogen have a lower electron affinity than oxygen?

Karen Ung 2H

According to the book, the ionization energy is the minimum amount of energy needed to remove an electron from a gas-phase atom, and electron affinity is the energy released when an electron is added to a gas-phase atom.

Karen Ung 2H

True or false? Electrons in an s-orbital are more effective than those in other orbitals at shielding other electrons from the nuclear charge because an electron in an s-orbital can penetrate to the nucleus of the atom. Will someone please explain why the answer is true in terms of the "shieldi...

Karen Ung 2H

@Madeline Musselman 3H
Hi, the correct answer for this delta V is 2 x 10^-39 m/s, so yes, it does have a negative exponent, but there may be an error in the set up of your equation or calculation.

Karen Ung 2H

Which one of the following statements is correct in describing Heisenberg's uncertainty (indeterminacy) equation? A. The less precisely the position is determined, the less precisely the momentum is known in this instant, and vice versa. B. The more precisely the position is determined, the more pre...

Karen Ung 2H

Why is copper different in that it doesn't follow the normal order (or pattern on the periodic table) of an electron configuration?

Karen Ung 2H

No, the magnetic quantum number does not only have three values. I believe the maximum number of values is seven (-3, -2, -1, 0, 1, 2, 3) because the f-orbital contains 14 electrons, giving it 7 subshells in the electron configuration.

Karen Ung 2H

"Light hits a sodium metal surface and the velocity of the ejected electron is 6.61 x 10^5 m.s-1. The work function for sodium is 150.6 kJ.mol-1. 29) How much energy is required to remove an electron from one sodium atom?" I believe the question asks for the work function, but I'm confused...

Karen Ung 2H

Because the higher energy state is not as stable, the electron has a tendency to move to the ground state, where it is in closer proximity to the protons, positively charged sub-particles.

Karen Ung 2H

I'm confused about when neither of the reactants is limiting in the chemical reaction. Could someone give an example/explanation?

Karen Ung 2H

We divide the mass of C, H, and O by 152.228g/mol in order to find the mass percent composition of each element. If there are 10 carbons in the formula, you would multiply 12.01*10 in order to find the total mass of carbon, which is 120.1g. Then divide by the total mass of the molecule to find the a...

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