CHEMISTRY COMMUNITY

Yvonne Du

For the snowflakes, delta H is negative because the snowflakes lose heat, and delta S is negative because going from a liquid to a solid is less chaotic. Negative delta H minus a negative delta S makes a negative delta G. For the sublimation, delta H is positive because heat is going in, and delta ...

Yvonne Du

I was wondering the same thing. Dr.Lavelle mentioned it during class, but I am still confused.

Yvonne Du

This really helped! I am glad that this question was asked.

Yvonne Du

When temperature increases, the Kw increases as well, which causes the neutral [H+] to increase and neutral pH to decrease. On the flip side, when temperature decreases, the Kw and neutral [H+] decrease, so the neutral pH increases. Neutral pH of 7 is only true at 298K. Thank you this is very helpf...

Yvonne Du

A catalyst is at the very beginning of the reaction and gets used; while intermediates only join in the later time and get used.

Yvonne Du

I asked my TA today, he said catalysts can be included in elementary step rate laws, but not the overall?

Yvonne Du

What is the exponential first-rate law?

Yvonne Du

Yes, just make sure that your units are consistent.

Yvonne Du

A catalyst is involved in the starting of the reaction, while an intermediate joins in later. Both of them are not included in the rate law. Today, my TA said that a catalyst can be included in the rate law. Can someone clarify? Sorry! I made a mistake. Yes it is possible for a catalyst to appear i...

Yvonne Du

Yes, if it is not one of the reactants of the first step, it would be an intermediate instead.

Yvonne Du

I think they are worth one point per question based on the midterm, so I think it is graded.

Yvonne Du

A catalyst is involved in the starting of the reaction, while an intermediate joins in later. Both of them are not included in the rate law.

Yvonne Du

A non-rechargeable battery is an example of galvanic cell

Yvonne Du

Basically the elementary steps help you determine the rate for the whole reaction. The step that has the slowest rate would be the rate for the whole reaction.

Yvonne Du

The new materials would weight more percentage I think.

Yvonne Du

The ln version might be more convenient, but both log and ln give the same ratio/result.

Yvonne Du

Since a combustion releases heat, you can therefore say that the reaction is exothermic and Gibbs free energy is negative

Yvonne Du

No, the coefficients do no effect order

Yvonne Du

Danielle_Gallandt3I wrote:This typically occurs when the reactant concentration is already very high, so adding more reactant doesn't change the rate

Thank you for clarifying!

Yvonne Du

It is not necessary, but make sure to keep the units constant.

Yvonne Du

If you know the lewis structures, it would be very helpful since you would know what bonds are breaking/forming.

Yvonne Du

When the temperature is constant, you can either use V2/V1 or P1/P2 depends on what you are given because in the formula PV=nRT, P and V has a proportional relationship.

Yvonne Du

Yes, qrev/Delta T would be the formula for irreversible reaction.

Yvonne Du

(Numbers of possible ways)^numbers of molecules.

Yvonne Du

Nope but the book covers pretty much everything that he mentions.

Yvonne Du

I think it might be 25 Celcius degree.

Yvonne Du

atm, but other units can also be used. Ps, different units of pressure are correspond to a different value of R.

Yvonne Du

They speed up the process but do not change the concentrations.

Yvonne Du

Since the volume is not changed after gas is being inserted, the partial pressure for each molecule is not changed therefore the equilibrium stays.

Yvonne Du

An exothermic reaction has a negative delta H while an endothermic reaction has a positive delta H. Delta H=Change in enthalpy.

Yvonne Du

The concentration of reactants and products(excluded solids and liquids) in the equilibrium state.

Yvonne Du

If the concentration of H+ or OH- is less than 5% of the concentration of HA or HB, you can ignore the x when it is being subtracted or added(i.e. 2-x=2).

Yvonne Du

Since the equilibrium constant(K) does not change, that means the ratio of product/reactant has to be constant. If you add more concentration to one of them, the other has to increase in order to make the ratio constant.

Yvonne Du

It depends on when your discussion session is. Test 1 should be in week 3 and test 2 should be in week 7

Yvonne Du

My TA said they dont affect equilibrium

Yvonne Du

Yes, one lone pair is considered as one electron density. Since hybridization is based on the number of electron density, you consider lone pairs too.

Yvonne Du

Since polarizing power describes the power of cations pulling electrons from the anions, small and highly charged cations would have a strong polarizing power to distort the electron clouds from the anions. Polarizability is the ability for anions to pull their electrons. Big and highly charged anio...

Yvonne Du

Lone pairs create strong repulsions since the charges are the same(negative). Therefore, they try to get away from each other and cause the bond angle to decrease. Also, the bonded atoms would most likely end up being close together since the lone pairs are getting away from each other.

Yvonne Du

6.9 Place the following types of molecular and ion interactions in order of increasing strength: (a) ion–dipole; (b) induceddipole–induced-dipole; (c) dipole–dipole in the gas phase; (d) ion–ion; (e) dipole–dipole in the solid phase. Can someone explain why is the order dipole-induced-dipole=dipole ...

Yvonne Du

You should try to give every atom an octet, then you can see if the formal charges are all equal to zero. If not, then check to see if the central atom is in 3p orbital, therefore, you can violate the octet rule. Most of the times the structure should satisfy both the octet rule and the formal charge.

Yvonne Du

A dipole is when a positively charged atom bonds with a negatively charged atom. The electronegative force between the two atoms is not the same, thus a dipole moment happens which is that one of the atoms is more electronegative than the other.

Yvonne Du

A sigma bond is the very first bond between two atoms, while pi bonds are the ones that come after the sigma bond. For example in a triple bond, there is one sigma bond and two pi bonds.
Hope this helps.

Yvonne Du

Yes, the lone pairs also affect the bond angles, and different type of VSEPR models have different bond angles.

Yvonne Du

In my notes I have that since H2O has two lone pair electrons and two pairs of bonding electrons, the lone pairs make the bond angle decrease a bit.

Hope this helps.

Yvonne Du

I think in the lecture we went over some notations about the VSEPR model: A=central atom X=bonded atom E=lone pair For example, AX3 is trigonal planar, AX2E2 is bend, AX4 is tetrahedral, AX4E is trigonal bipyramidal, and AX4E2 is Square planer. I think remembering these can save you some time. Hope ...

Yvonne Du

For 6th edition, do we also study chapter 6.4 and 6.5?

Yvonne Du

Elle_Mendelson_4I wrote:Will someone explain 10A?

As more electrons and photons are added to the atom from left to right, the force of increasing protons creates a stronger pull that attracts the electrons to get closer to the nucleus. Therefore the atom shrinks for silicon and has a smaller radius than aluminum.

Yvonne Du

For number 5, I keep getting .127 M after setting the problem up like (.211 M)(.150 L) = M2(.250 L). But in my notes, I believe Lyndon got 1.69 x 10^-2. I was wondering if anyone knows what I am doing wrong. Thanks! Hi! Since the problem stated that only 20ml was removed to the 2nd flask, you put 0...

Yvonne Du

The resonance structures should be equally stable. However, the Lewis structure for this specific compound does not represent its real appearance because a compound that has resonance structures actually have the resonance bond constantly changing from atom to atom, so that is why we said we can hav...

Yvonne Du

1)Convert 102.6nm to 1.03*10^-7m.
2)Use c=v*lamda to find the frequency.
3)Use Rydberg formula, v=R(1/(n^2)-1/(n^2)) to find n2. Note that the first n is n1 and the second n is n2.
4)Since it's Lyman's series, you know n1=1.

Yvonne Du

For number 5, I keep getting .127 M after setting the problem up like (.211 M)(.150 L) = M2(.250 L). But in my notes, I believe Lyndon got 1.69 x 10^-2. I was wondering if anyone knows what I am doing wrong. Thanks! Hi! Since the problem stated that only 20ml was removed to the 2nd flask, you put 0...

Yvonne Du

Hi can anyone explain 8a? I don't know how to correctly word my answers...

Yvonne Du

You remove electrons starting with the highest level. Since there is only one electron in the 4s shell, you need to subtract another electron from the 3d shell.

Hope this helps.

Yvonne Du

For your first example, the whole 5p1 represents one electron only. In the future, you can know the number of electrons in each shell by looking at their superscript. For example, 5p5 means there are 5 electrons in the 5p shell. For your second example, p shells contain 6 electrons in total. In orde...

Yvonne Du

I think in the book they stated that it should be n(initial)-n(final). I ran into the same problem. For one of the homework questions, I got a negative answer when I put n(initial)-n(final), but the answer key says it is positive. They flipped the other to get a positive number. I think I'll go with...

Yvonne Du

I have the same question too.

Yvonne Du

I think you should at least be familiar with it. Even though we didn't do too much on those topics, but it doesn't hurt to learn a little more.

Yvonne Du

I think you should be familiar with them, but don't try too hard to memorize them. I would recommend knowing the E of photon formula, De Broglie Equation, the Uncertainty Principle, and the Photoelectric effect.

Yvonne Du

Yes, short wavelength lights have high frequency and long wavelength lights have low frequency. This can be proved by using the electromagnetic equation c=vλ where c is the speed of light, v is the frequency, and λ is the wavelength. They have a universal relationship.

Yvonne Du

In order to balance a chemical equation, you need to figure out the reactants and products first. In this case, you only have one compound which means this is not a chemical equation. After you have had all the reactants and products, you can then try to come up with accurate coefficients in front o...

Yvonne Du

How do you know which is the initial molarity, initial volume, final molarity, and/or final volume from a given problem? How do you figure it out? I think most of the questions will state them if not, you can look for hints in the question. For example, if the question is adding water to dilute the...

Yvonne Du

Yes. For example, if the question asks you to convert 2.0g of CO2 to moles. What you do is first add up the molar mass for CO2 which is 12.011(C)+15.999*2(O)=44.009grams. Then you use 2/44.009 to get the moles. You always consider the subscripts.

Yvonne Du

When asked to look for Molarity/volume/moles, one of the common equation that we use is M=moles/volume. You are given the moles and molarity, which means you can use this formula to find the volume.

Yvonne Du

I think as long as your answer is close enough to the book answer, TAs won't make you wrong. In this case, your answer is very close.

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