CHEMISTRY COMMUNITY

jonathanjchang2E

To find the equation for a 1st order reaction half-life you use t1/2=(1/k)(ln([A]initial/.5[A]initial)). In order to find a _%-life equation for any 1st order reaction just substitute _% for the .5 in the half-life equation. The solutions manual used this idea to answer the question and in A and B, ...

jonathanjchang2E

The half-life for a 1st order reaction is t1/2= ln2/k. The 10%-life for a 1st order reaction is t1/10= ln10/k. To find the answer, solve for k for both the half-life and 10%-life equations and equal both the equations together since k should be the same. Then plug in 70 days for t1/2 and solve for t...

jonathanjchang2E

I had that problem too. You have to convert all of the concentrations to mol/L and the rates to mol/(L*s). Also, the answers in the back of the book should be in mol not mmol.

jonathanjchang2E

Zero order reaction: Rate of the reaction is independent of the concentration of the reactants. rate=k First order reaction: Rate of the chemical reaction is directly proportional to the concentration of the reactants. rate=k[A] The order is just the exponent of the concentration of one of the subst...

jonathanjchang2E

The equation t1/2=0.693/k is only used for 1st order reactions.

jonathanjchang2E

The plot is an exponential curve because as the reaction progresses, there are fewer and fewer reactants and the reaction rate decreases. The reaction rate decreases because there are fewer successful collisions between the reactants to form products since there are fewer reactants as time goes on.

jonathanjchang2E

Both ways are correct, but it would be better if you left the electrons on the reactant side of the reaction so that you don't mix up the signs of the standard reduction potential.

jonathanjchang2E

The carbons have different charges because a carbon's oxidation number can change in a reaction while the oxidation number of oxygen is almost always -2 and the oxidation of hydrogen is almost always +1.

jonathanjchang2E

First you separate and balance the two half reactions. The oxidation half reaction is C2H5OH -> C2H4O. You know this because the oxidation number of carbon in the first molecule is -2 and in the product molecule, it's -1. You then balance the half reaction by adding H+ and e- and you should get C2H5...

jonathanjchang2E

If you look at the list of thermodynamic data in appendix 2a you'll find that most compounds have a negative delta G (formation), not only gases.

jonathanjchang2E

You can also come up with equations based off of the information given by the question. From this you can check if the given information matches up with any equation on the equation sheet and if the information matches with multiple equations, you can combine equations to generate a new one.

jonathanjchang2E

The reaction shifts to the reactants side because more O2 is added and according to Le Chatelier's, adding a product should cause more reactants should be formed.

jonathanjchang2E

In most situations both would work, but if you use the wrong one you would just have to convert the R you used to the other R through 101.325.

jonathanjchang2E

The problem may have said constant pressure in reference to the irreversible path of expansion.

jonathanjchang2E

The units of the coefficients for the reaction are not mols. "4 KClO3" may be 4 moles of KClO3 but the 4 by itself is not in mols"

jonathanjchang2E

The ice cube is already at 0 degrees celsius so it goes through a phase change to liquid before its temperature (as a liquid) raises to the final temperature of the system.

jonathanjchang2E

Usually the question will not specifically say whether or not the gas is an ideal gas, but for most cases we just assume the gas is ideal and continue using the equation. This is better explained on page 266 of the 6th edition book.

jonathanjchang2E

The 3/2 coefficient comes from the equipartition theorem which states, "The average value of each quadratic contribution to the energy of a molecule in a sample at a temperature T is equal to (1/2)kT" and since there are three translational modes of motion, each giving a quadratic contribu...

jonathanjchang2E

Q: When one physicist asks another, "What's new?" what's the typical response?
A: C over lambda.

jonathanjchang2E

Did you know that you can cool yourself to -273.15˚C and still be 0k?

jonathanjchang2E

We know that part a in 8.11 is referring to irreversible expansion because the gas is expanding against a constant pressure of 1 atm. In a reversible expansion, the external pressure is always equal to the pressure of the gas.

jonathanjchang2E

The pH of a solution with salt depends on the relative acidity and basicity of the salt's ions.

jonathanjchang2E

More product will be made if there are more moles on the reactant side than the product side and pressure is increased/volume is decreased. More product will also be formed if the reaction is endothermic and heat is added to the system. Also if more of one reactant is added, then usually more produc...

jonathanjchang2E

Yes, if you need more clarification it is explained on page 441 of the 6th edition textbook in toolbox 11.1.

jonathanjchang2E

You find the coefficients by setting up an ice table since they give you the initial and final partial pressures. So the initial for A is 28, B is 0, and C is 0. The final for A is 18, B is 5, and C is 10. From this you know that the change for A is -2X, for B is +X, and C is +2X because it would on...

jonathanjchang2E

You can predict if a reaction is endothermic or exothermic by looking at the energies of the reactants and products (but this way is really hard with more complicated reactions). For example if you're given H2 = 2H, it would probably be endothermic since H2 is lower in energy than 2 H.

jonathanjchang2E

They are the same in some cases and different in others. If you look at table 11.2 on page 428 in the sixth edition of the book, some values of Kc and Kp are the same and some are different even thought its the same chemical reaction.

jonathanjchang2E

Yes, chemical reactions always head towards equilibrium even though it may take a long time to reach it. When reactions go to completion, they still reach equilibrium. It's just that the constant rate of the forward reaction is extremely greater than the constant rate of the reverse reaction, so muc...

jonathanjchang2E

Equilibrium constants give us an indication of where the equilibrium lays. So if K>1, the reaction has a greater concentration of products compared to reactants and if K<1, the reaction has a greater concentration of reactants.

jonathanjchang2E

It doesn't matter if you use partial pressure or concentration unless the question specifically says Kc or Kp. Yes, the coefficient in the formula is always in the exponent regardless of which K you're solving for.

jonathanjchang2E

It is also helpful to look at the element's group in the periodic table when determining their ionic form.

jonathanjchang2E

For your example problem, anything that weakens the O-H bond would cause the molecule to be a stronger acid. So the answer would be HClO<HClO2<HClO3<HClO4 due to the impact the added oxygen atoms have on the O-H bond. This is generally the same idea with bases as molecules that dissociate more easil...

jonathanjchang2E

Sigma bonds acts like joints which allows for rotation in a molecule, but pi bonds are like two parallel joints and if you try to turn only one joint, you wouldn't be able to because of the other "joint" in the pi bond.

jonathanjchang2E

You're right, the ClO2 lewis structure with two double bonds is the most stable.

jonathanjchang2E

Hybridization occurs because hybridized orbitals are lower in energy than unhybridized ones so they are favored when forming molecules.

jonathanjchang2E

Yes, the textbook is the same.

jonathanjchang2E

It tends to make it stronger since larger molecules tend to have larger london forces due to the greater amount of electrons, but the strength of a molecule is dependent on many other things besides size.

jonathanjchang2E

The solution manual considers the more stable structure with the double bond with Oxygen but since the lesson primarily focuses on shape, they accepted both structures.

jonathanjchang2E

The tetrahedral molecule has a dipole moment if one of the outer atoms is heavier than the others. For example, CH3Cl is polar because of the greater amount of electrons on the Cl than the three H atoms. If the non-central atoms are all the same like in CH4 or CCl4 the molecule will be nonpolar beca...

jonathanjchang2E

Drawing out the lewis structure definitely helps in determining the shape of the molecule and I think it's best if you go that route until you're confident enough to determine the shape without drawing the lewis structure.

jonathanjchang2E

You can determine the intermolecular forces on most molecules just by its chemical equation. For example, if the molecule has hydrogen and N,O, or F it has hydrogen bonding. If the molecule is polar like CHCL3 then it will have dipole dipole interaction and all molecules are able to have London inte...

jonathanjchang2E

I don't think you can get away without remembering the names of the different shapes but it is helpful to know the lewis structures and bonds and lone pairs when determining the shape.

jonathanjchang2E

The fourth valence electron in oxygen's p orbitals has a lower ionization energy because of the electron electron repulsion formed by the lower three valence electrons. This ionization energy is lower than nitrogen because of the three parallel electrons in nitrogen's p orbitals.

jonathanjchang2E

http://2.bp.blogspot.com/_DZH2cmCoois/R ... thanol.bmp this link has the lewis structure

jonathanjchang2E

No, hypo- is a common prefix used to name the lowest number of atoms for a certain polyatomic ion group. For example, perchlorate = ClO4-, chlorate=ClO3-, chlorite=ClO2-, hypochlorite=ClO-. I think Dr. Lavelle will go more in depth on this later.

jonathanjchang2E

Bond lengths are usually given on questions and if they are asking to find the bond length of lewis structures, you have to take into consideration resonance structures.

jonathanjchang2E

Yes, this is one of the electron configuration exceptions. A half full d and full d subshell have lower energy than the s subshell in periods 4 and up (5+) so the electrons will tend to occupy 4d before 5s.

jonathanjchang2E

The resonance hybrid shows the delocalized electrons in a molecule and it is a representation of the sum of all the resonance structures.

jonathanjchang2E

The positive or negative formal charge of an element is based on the surrounding electrons (bonded or lone pairs), but the formal charges of electrons in a molecule can "cancel" each other out resulting in a net charge of 0 for the molecule.

jonathanjchang2E

Since isoelectronic atoms and ions have the same number of valence electrons they should display similar chemical properties. For example, hydrogen and hydrogen-like atoms such as Li2+ display similar properties since they both have only one electron.

jonathanjchang2E

Yeah you're right. The electrons closest to the nucleus do have lower energy, which is why the electrons in the 2s orbital are lower in energy than the electrons in the 2p orbital. The electrons in the 2p orbital are shielded by the electrons in the 2s orbital, which cause the 2p orbital electrons t...

jonathanjchang2E

A question might ask you to name the spectroscopic series to which the transition of radiation from n=4 to n=2 belongs and I guess you would just have to know that this transition belongs to the Balmer Series.

jonathanjchang2E

The nodal plane is an area that goes through the nucleus where no electrons will be found. It separates lobes of orbitals and on the nodal plane "psi" is equal to 0.

jonathanjchang2E

The question asks to calculate the wavelength and since the majority of the wavelengths on the electromagnetic radiation spectrum range from ~300nm to ~1000nm it would only make sense for the answer to be in between those two numbers and have three significant figures, but in this case, I don't thin...

jonathanjchang2E

Conceptually we should think of the equation as having the greater than or equal sign but when we do problems involving the Heisenberg Uncertainty Principle we generally only use the equal sign.">" only tells us that the product of the uncertainty in position and the uncertainty in linear ...

jonathanjchang2E

I don't think multiple choice questions are as stringent on significant figures.

jonathanjchang2E

All metals have a specific work function or threshold, which is the minimum energy required to eject an electron. Shorter wavelengths usually have an energy greater than the threshold whereas longer wavelengths do not, which is why light with shorter wavelengths are more commonly able to eject elect...

jonathanjchang2E

How do you solve question 1.27? Here's the question: "A lamp rated at 32 W (1 W = 1 J*S^-1) emits violet light of wavelength 420 nm. How many photons of violet light can the lamp generate in 2.0 s? How many moles of photon are emitted in that time interval?"

jonathanjchang2E

n is the moles of solute

jonathanjchang2E

Yeah, since the question asks for the amount of F^- ions and there are 6 moles of F^- ions for every one mole of UF6 we would have to multiply the amount (in moles) of UF6 by 6. Also, yes for your second question.

jonathanjchang2E

I'm pretty sure the Audio-Visual Focus-Topics, Assessments & Surveys do not affect our grades. They're just supplemental questions and videos to assist with the coursework.

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