CHEMISTRY COMMUNITY

Douglas Nguyen 2J

Hehe, I remember this problem. I just sat there and then finally remembered the chemical notation for phosphoric acid.

Douglas Nguyen 2J

A cool note I found while surfing the web was that a catalyst first shows up as a reactant and reappears as a product whereas an intermediate first shows up as a product and is cancelled out when it appears as a reactant in the next step.

Douglas Nguyen 2J

A pseudo rate is considered when there are too many changing concentrations. For instance, it is difficult to calculate the rate when you have k[A][B], and both A and B are changing. As such, you make one significantly larger so that the rate becomes dependent on only the other. For this example, le...

Douglas Nguyen 2J

Yes, both zero and first order reactions' linear plots have slope as -k.

Douglas Nguyen 2J

q is equal to delta H when pressure is constant.

This gives you:

delta U = delta H - P(delta V)

Douglas Nguyen 2J

We can use the stoichiometric coefficients when writing the rate law for elementary steps but not for the overall reaction. Given the overall reaction, the exponents on the concentrations for the rate law do not necessarily have to match the coefficients.

Douglas Nguyen 2J

No heat is gained or lost by the system, so q=o and delta U = w.

Douglas Nguyen 2J

Half-life is the amount of time it takes for a species to be reduced to half of its concentration!

Douglas Nguyen 2J

To determine to order of increasing reducing power, you can reference the standard reduction potential sheet that is given during the test (or in the textbook in appendix 2B). Standard reduction potential is an element's/compound's inclination to be reduced, and the more positive the potential, the ...

Douglas Nguyen 2J

Injecting an inert gas will change the total pressure of the system, but it will not change the partial pressures of the other compounds/elements. As such, the equilibrium constant doesn't change!

Douglas Nguyen 2J

In an eletrolytic cell, you're converting electrical energy into chemical energy, and in a galvanic cell, you're converting chemical energy into electrical energy!

Douglas Nguyen 2J

Since test 2 only covers material up to the Nernst equation, which homework problems (6th edition) from the outline should be practiced? (number 1-?)

Douglas Nguyen 2J

In the instance that you have two ions both aqueous both in the same cell, what order would you write them?

ex:

Pt(s) I Ti(3+)(aq), Ti(2+)(aq) II....

or

Pt(s) I Ti(2+)(aq), Ti(3+)(aq) II....

Douglas Nguyen 2J

Definitely electrochemistry because I struggled more with the electrochem homework problems in comparison to Gibbs Free Energy.

Douglas Nguyen 2J

Going over the homework problems to ensure that I know the key concepts, reviewing the notes, and if time permits, check out the worksheets that UAs post on C. Community.

bless you for this question

Douglas Nguyen 2J

In the instance that they cancel out, you do not include them. If they do not completely cancel each other out, include them.

Douglas Nguyen 2J

What are the steps you take to balance this reduction reaction?

P4(s) -> H2PO2(-) +PH3(g)

I have:
12e- + P4(s) -> 4PH3(g)

and then:

12e- + P4(s) + 6 H2O -> 4PH3(g) + 6 OH-

but the solutions manual indicates that the reduction reaction requires 12 water and 12 hydroxide ions.

Douglas Nguyen 2J

The question is just testing your knowledge that q(sys)=-q(surr). It doesn't matter where the negative sign goes.

Douglas Nguyen 2J

I tell biology jokes because all of the chemistry ones argon!

Douglas Nguyen 2J

Edgar Olivera, the TA for 2J, said that we may receive our midterms back by Wednesday of this week and Friday at the latest.

Douglas Nguyen 2J

What is U(tot)=(3/2)nRT refer to?

Douglas Nguyen 2J

In that instance, you can determine which has a higher molar entropy with which one has greater mass, and since it has greater mass, it also has more elementary particles!

Douglas Nguyen 2J

How do vibrational, translational, and vibrational motion relate to entropy and enthalpy?

Douglas Nguyen 2J

"9.25 If SO2F2 adopts a positionally disordered arrangement in its crystal form, what might its residual molar entropy be?" When calculating entropy using S=k(b)lnW, the solutions manual states that W is 6^(6.02214*10^23). Is the exponent just based on the number of molecules/units involve...

Douglas Nguyen 2J

What is the difference between CV,m and CP,m? What do they signify aside from being the heat capacity of gasses?

Douglas Nguyen 2J

Delta U signifies the change in internal energy.
q refers to the energy transferred by heating.
w is the energy transferred by compression.

Douglas Nguyen 2J

8.9 "An ideal gas in a cylinder was placed in a heater and gained 5.50 kJ of energy as heat. If the cylinder increased in volume from 345 mL to 1846 mL against an atmospheric pressure of 750. Torr during this process, what is the change in internal energy of the gas in the cylinder?" For t...

Douglas Nguyen 2J

What's the difference between "work done by" and "work done on a system"?

Douglas Nguyen 2J

You can consult the Constants and Equations sheet on Dr. Lavelle's website too! It's pretty handy to use while you do your homework so that you're used to it when taking tests:

https://lavelle.chem.ucla.edu/wp-conten ... ations.pdf

Douglas Nguyen 2J

The CH4 isn't placed in the vessel but rather is produced through the chemical reaction involving CO and H2.

Douglas Nguyen 2J

Acids and bases are subject to chemical equilibrium in that under certain conditions, acids and bases produce a discrete amount of hydronium or hydroxide ions.

Douglas Nguyen 2J

The initial values given for the question were 0.0073 M of codeine and pKa of conjugate acid was 8.21. With that, I assumed there were 2 significant figures (0.0073). The answer was: 1.5%, 3.96, 10.04 For 10.04, does ".04" count as two significant figures since it's after the decimal point...

Douglas Nguyen 2J

12.39: Using data in Tables 12.1 and 12.2, place the following acids in order of increasing strength: HNO2, HClO2, +NH3OH, (CH3)2NH2+" How would you go about solving this problem? I referred to the table in the textbook and got the values for HNO2 and HClO2, but the last two aren't listed. What...

Douglas Nguyen 2J

A strong acid will dissociate completely whereas a weak acid will not. Weak acids have a K constant <10^-3.

Douglas Nguyen 2J

Is autoprotolysis a process that is exclusive to water or can other molecules perform autoprotolysis?

Douglas Nguyen 2J

12.23: The value of Kw for water at body temperature (37 C) is 2.1*10^(-14) mol*L-1. (a) What is the molarity of H3O+ ions and the pH of neutral water at 37 C? I calculated the pH, and I got 6.838890353; when rounding, I should get 6.83, but the textbook says the answer is 6.80. Can someone please e...

Douglas Nguyen 2J

Which outlines will be on test 1? Just trying to mentally and physically prepare myself

Douglas Nguyen 2J

The 1 and the 61.0 are because it is a reversible reaction. 61.0 is the equilibrium constant of the forward reaction, and the reverse reaction's equilibrium constant is just the inverse of the forward reaction's equilbrium constant.

Forward reaction: 61.0; reverse reaction: 1/61.0

Douglas Nguyen 2J

For the answers in question 11.13, is there a particular reason as to why for parts a and c are written using partial pressures and part b is written with molar concentrations?

11.13: "Write the reaction quotient Q for..."

Douglas Nguyen 2J

On question 2 of the quantum world exam, the question asks: "The uncertainty in the momentum (delta p) of a cricket ball which is traveling at 150 km/hr is 2 x 10(-6) times its momentum. Its mass is 0.160 kg. Calculate its minimum delta x." How many significant figures should the answer ha...

Douglas Nguyen 2J

NH3 will have a greater boiling point than PH3 because of hydrogen bonding. NH3 is capable of having hydrogen bonds and PH3 is not because nitrogen is significantly more electronegative, thus creating a dipole moment with a partial positive charge on the hydrogens and a partial negative charge on th...

Douglas Nguyen 2J

I would say they're pretty important seeing as points have been deducted on exams for incorrect significant figures. Reference guides on how to calculate significant figures are on Professor Lavelle's website.

Douglas Nguyen 2J

Polydentate means that a ligand is able to occupy multiple bonding sites at once because it has lone pairs. So applying the Greek prefixes, a monodentate binds to one bonding site, and bidentate bonds to two.

Douglas Nguyen 2J

Friday, December 7th is exclusively for past exam questions. Dr. Lavelle told lecture 1 that the last day of instruction covering new material would be the Wednesday of that week.

Happy studying! :)(((

Douglas Nguyen 2J

In the 6th edition on page 741, the textbook names [FeCl(OH2)5)+ as pentaaquachlridoiron(II) ion and [Fe(NCS)(OH2)5]2+ as thiocynato(kN)pentaaqua(III) iron. What is the reasoning behind placing the oxidation number after the name in the former and before the TM in the latter? Is it because the forme...

Douglas Nguyen 2J

How are coordinate covalent bonds formed?

Douglas Nguyen 2J

MMoreno3K wrote:Does anyone know the specific topics that will be on the test?

On the class website, it is written that "Test 3 covers: End of Bonding from 3.12 (6 Ed.) and from 2D (7 Ed.); and all of Molecular Shape and Structure (see Syllabus and Outlines for details)."

Good luck with your studies!

Douglas Nguyen 2J

Can someone please explain to me what exactly dipole means? A dipole moment is an electrical movement from one atom toward one adjacent atom. Dipole moments do not occur with diatomic molecules because the two atoms have the same electronegativity. Dipole moments also determine covalent bond disass...

Douglas Nguyen 2J

"On a plot of the potential energy of a diatomic molecule as a function of the internuclear distance, the dissociation energy is the distance between the bottom of the energy well and the energy of the separated atoms" (93, 6th E.). Would someone be able to explain this to me in layman ter...

Douglas Nguyen 2J

LOL I cannot do math. I'm leaving this school.

Douglas Nguyen 2J

"4.19 Predict the shapes and estimate the bond angles of...(d) SnCl2."

In the Lewis dot structure for SnCl2, tin is drawn to only have 6 electrons. Why is it that tin is an exception to the octet rule?

Douglas Nguyen 2J

For the "ABE" notation (A being the central atom, B being atoms bonded to the central atom, and E being lone electron pairs around the central atom), how is it written for radicals? ex: "4.19 Predict the shapes and estimate the bond angles of...(c) BH(2)-" BH(2)- has only 5 elect...

Douglas Nguyen 2J

"Predict the bond angles at the central atom of the following molecules and ions:...d) hydronium ion, H3O+."

I was able to understand that the shape of this molecule is a tetrahedral, but why is it that the bond angle is "slightly less than 109.5" rather than 109.5?

Douglas Nguyen 2J

we know that orbitals are given by s, p, d, and f subshells, and we know that each of these can hold 2, 6, 10, and 14 electrons, respectively. But where do those numbers come from? Each orbital is capable of holding 2 electrons. The magnetic quantum number (m(l)) depicts the orientation/# of orbita...

Douglas Nguyen 2J

Can someone explain to me why smaller and more highly charged cations have more polarizing power? Smaller, more highly charged cations have more polarizing power because these cations cause larger distortions since the more highly charged the cation, the greater the electrostatic attraction is exhi...

Douglas Nguyen 2J

How do we determine the energy of each bond? For example when we did the Lewis structure of Benzene in one of the double bonds we put it was 1.34 A and the single bond was 1.54 A. The energy of a bond is equal to the energy needed to break it due to the conservation of energy. The energy of a bond ...

Douglas Nguyen 2J

Why is it that a Ca^2+ ion is smaller than a Na+ ion? An [Na]+ ion has 11 protons and 10 electrons whereas [Ca]2+ has 20 protons and 18 electrons. Although the periodic trends dictate that as you go down a group, the atomic radius increases due to increased shielding and energy levels, the Z-effect...

Douglas Nguyen 2J

Since both ionization energy and electronegativity are the energies to remove an electron, then what is the difference between them? Does ionization energy refer only to ionic bonds and electronegativity refers to covalent bonds? Both of them follow the same trend on the periodic table: both increa...

Douglas Nguyen 2J

Hello! I thought energy could only be positive, why does the equation for energy at a specific principle quantum number have a negative sign in front of it? Is this applied to find change in energy? En = -hR/n^2 Because when applied to delta E=E(final)-E(initial), delta E is energy emitted. It is u...

Douglas Nguyen 2J

There is no particular order by which you should draw your Lewis dot structure; a rule you should be wary of is Hund's rule, which states that due to e- repulsion, e- in same subshell will occupy different orbitals and with parallel spin because it gives the lowest energy.

Douglas Nguyen 2J

A good reminder of how many valence electrons is to look at the group number, which is typically indicated above the top element of each column. Group 1 has 1 valence electron, 2 has 2 electrons, 13 has 3, 14 has 4, 15 has 5....18 has 8. Groups 3-12, which are the transition metals, behave different...

Douglas Nguyen 2J

To add a note to the previous comments, it's beneficial to acknowledge that the formula "c=lambda*frequency" is only applicable to photons because only light can travel at that speed. You shouldn't apply that formula to particles that aren't photons.

Douglas Nguyen 2J

When using DeBroglie's equation do you have to calculate given values into certain units before putting them into the equation? DeBroglie's wavelength formula is lambda=h/mv. Lambda (wavelength) must be in meters but can be converted after the calculation if the question asks for a different unit.P...

Douglas Nguyen 2J

Could someone explain to me when I would use hR/n^2? You would use the that formula, which is exclusive to hydrogen atoms, when attempting to calculate energy levels or energy output. A few of the questions in the textbook use this formula as a means to eventually find the energy to find the wavele...

Douglas Nguyen 2J

1.23 asks "The gamma-ray photons emitted by the nuclear decay of a technetium-99 atom used in radio-pharmaceuticals have an energy of 140.511 keV. Calculate the wavelength of these gamma-rays."

What is the conversion from an electron volt to a Joule?

Douglas Nguyen 2J

"I understand that Dr. Lavelle explained this during lecture, however, I am still a bit confused. Can someone please explain how an electron is able to reach the detector if there is 0 Kinetic energy. Is there an attractive force of some sort?" As Dr. Lavelle explained, this experiment wou...

Douglas Nguyen 2J

"I cannot conceptualize light being both photon (PACKETS) of energy and wavelengths. I find it difficult to exercise this into equations when I do not understand how it can be both and have one number. Please explain and possibly use equations in your explanation if possible. If not that is oka...

Douglas Nguyen 2J

For the photoelectric effect, a shorter wavelength means a higher frequency. Higher frequency equates to a greater amount of energy in the photon, and thus, an electron is ejected because sufficient energy was provided. E=hv

Douglas Nguyen 2J

Because without significant figures, the equipment we use to make measurements would appear to be more accurate than they truly are.

Douglas Nguyen 2J

In Fundamentals L, question 39 is as follows: "A 1.50-g sample of metallic tin was placed in a 26.45-g crucible and heated until all the tin had reacted with the oxygen in air to form an oxide. The crucible and product together were found to weigh 28.35 g. (a) What is the empirical formula of t...

Douglas Nguyen 2J

In Fundamentals L, question 35 asks "What mass of iron, in kilograms, is needed to produce 2.50 t of NaBR?"

My question is what unit of mass is "t" shorthand for?

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