CHEMISTRY COMMUNITY

Beatrice Petelo 1F

Thank you Dr. Lavelle for your assistance and patience. It has been a pleasure to be your student for the past two quarters!

Beatrice Petelo 1F

What does the arrhenius equation determine and what would we use this equation for?

Beatrice Petelo 1F

Why is the slow elementary step the rate-determining step and not the faster step?

Beatrice Petelo 1F

Can someone please explain how you would approach this problem? I was not sure on what to do with the change in enthalpy and Kw.

Beatrice Petelo 1F

They are used interchangeably, but log is usually associated with pH!

Beatrice Petelo 1F

Can someone explain the difference between instantaneous, unique, differential, and average rate laws? How do we know when to use which?

Beatrice Petelo 1F

I believe we just need to know the simple derivative and integral rules.

Beatrice Petelo 1F

Why do we need to conduct experiments to determine the rate law?

Beatrice Petelo 1F

First, you would have to write the half reactions and balance them. From there, you can figure out which is the anode and cathode and determine the E potentials from the back of the textbook. You might have to switch the direction of the anode, and therefore flip the sign of the E potential. The for...

Beatrice Petelo 1F

Joules or kj. I've also seen j/mol or kj/mol depending on the problem

Beatrice Petelo 1F

closed systems - exchange only energy
examples: pressure cooker, thermometer, pot with lid

isolated systems - does not exchange matter and energy
examples: thermos

Beatrice Petelo 1F

I believe so. We write it in the order of solids|gases|liquids|aqueous || aqueous|gases|liquid|solids

Beatrice Petelo 1F

Why do we use the Van't Hoff equation? What does it tell us in terms of K and temperature?

Beatrice Petelo 1F

What are the signs for gibbs free energy for both spontaneous and non-spontaneous reactions?

Beatrice Petelo 1F

It will take about a week to grade!

Beatrice Petelo 1F

I think you meant residual entropy (idk if there is a difference between residual energy and residual entropy haha). Residual entropy is the entropy at T=0 K. You can solve for it by using S=Kb*lnw (s=entropy, kb=boltzmann constant, w=degeneracy which is # of orientations^# of molecules). Degeneracy...

Beatrice Petelo 1F

Joules is also equal to N*m and (kg*m^2)/s^2. Not sure if we are required to know those. I haven't encountered a problem where we had to do that

Beatrice Petelo 1F

Hi!

Can someone please explain the difference between reversible and irreversible expansion and how we are able to differentiate between the two

Thanks!

Beatrice Petelo 1F

If you are referring to the (3/2)R constant for the ideal gas, Cv, you would use that when volume is constant.

Beatrice Petelo 1F

Any advice to approaching calorimetry problems and differentiating between which constant (constant pressure/volume and specific/molar heat capacities) to use?

Thanks!

Beatrice Petelo 1F

It will probably go until the end of 2nd&3rd law of thermo (or maybe halfway i just looked at the syllabus and there are a lot of topics haha) because we were just introduced to entropy at the end of Friday's lecture.

Beatrice Petelo 1F

You can pick them up at a window/office on the third floor of Young Hall. It’ll be easier to find if you use the right side entrance that’s facing the Court of Sciences.

Beatrice Petelo 1F

Acids tend to have an H and bases OH

Also, the Bronsted-Lowry definition:
acid: proton (H+ ion) donor
base: proton acceptor

Beatrice Petelo 1F

How does ∆Hsub=∆Hfus+∆Hvap work?
Thanks!

Beatrice Petelo 1F

When there is an increase in pressure, the reaction will occur in the direction w/ fewer moles of gas.

Beatrice Petelo 1F

The solutions manual says to add reactions 1 and 2 together. Where does the Cl2 go when you do this step?
Also, why do we multiply the two K values together?

Beatrice Petelo 1F

Either one, as long as it's relevant to what we're learning in class and not too far ahead.

Beatrice Petelo 1F

Why does the value of K not change when we change the concentration of reactants or products?

Beatrice Petelo 1F

When calculating for K, do we use the initial or equilibrium concentrations?

Beatrice Petelo 1F

I noticed that when calculating K/Kc in questions 11.3 and 11.9 (6th edition), the solutions had either brackets or parentheses. Is there a difference between the two? How would I know which one to use?

Beatrice Petelo 1F

Are we required to know the transition metals (such as Cr, Fe, Co, Mn, Ni, Cu, and Zn) and their functions for the final?

Beatrice Petelo 1F

the brackets indicate that the contents inside are the coordination compound. I assume that sodium is not part of it.

Beatrice Petelo 1F

How do we know when to include roman numerals when naming?

Beatrice Petelo 1F

Bronsted-Lowry definition:
acid: proton (H+ ion) donor
base: proton acceptor

Lewis definition:
acid: electron acceptor
base: electron donor

Beatrice Petelo 1F

According to the chem 14a website, "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)."

Beatrice Petelo 1F

In polar covalent bonds, electrons are not equally shared. Thus, there is a charge difference in electronegativities and a dipole moment is formed.

In nonpolar covalent bonds, electrons are equally shared and there is no charge difference.

Beatrice Petelo 1F

The solutions manual doesn't give a clear answer on how many bond angles there are for the molecule, SOCl2. Would there be two bond angles, one for the O-S-CL bonds and the CL-S-CL? Or does the lone pair on the S alter the angle because of repulsion, thus there is only one bond angle in the molecule...

Beatrice Petelo 1F

Do we take into account resonance structures when determining the lewis structure and vsepr model of a molecule?

Beatrice Petelo 1F

How can you determine whether or not the three different structures are polar or nonpolar?
Also, how can the dipole moment be determined based on the figures?

Beatrice Petelo 1F

In polar molecules, dipoles do not cancel (e.g. CHCl3). The lewis structure of this molecule has one side that is more electronegative (Cl) than the other (H). An arrow would be drawn towards the more electronegative side -- Cl, indicating a dipole moment.

Beatrice Petelo 1F

The negative sign has to do with the potential energy decreasing due to the interactions occurring in London Forces. This decrease in energy is dependent on the distance between the two molecules that are interacting. If you want to read more on it, pages 191-196 (page 195 specifically on London For...

Beatrice Petelo 1F

What causes a bond angle to be less than their ideal values?

Beatrice Petelo 1F

Dipole moments occur when there is a difference in charge between the two atoms or ions. The smaller the difference in electronegativity, the smaller the dipole moment is. The larger the difference in electronegativity, the larger the dipole moment.

Beatrice Petelo 1F

Can someone please explain the relationship between bond length and bond order? And bond strength and bond order?

Thank you!

Beatrice Petelo 1F

SydBenedict3H wrote:So the shorter the bond,the stronger it also is?

Yes. Multiple bonds are shorter than single bonds. Adding bonding electrons attract nuclei more and pulls the atoms closer.

Beatrice Petelo 1F

Bonds form between two atoms when: 1. orbital on one atom occupies the same region of space as an orbital on the other atom. When this occurs, the two orbitals overlap. 2. total # of electrons in both orbitals is no more than two sigma bonds: two atomic orbitals overlap head-to-head - These are cyli...

Beatrice Petelo 1F

The TA and UA sessions I've been to just said that the only exceptions we need to know are chromium and copper.

Beatrice Petelo 1F

1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 5p10 This diagram tells you the order of filling out orbitals on the energy level diagram or electron configurations. For example, when you draw out the diagonal arrows, you would get 1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d10, 4p6, etc. You don't really need th...

Beatrice Petelo 1F

The electron configuration for Tungsten is [Xe] 4f^14 5d^4 6s^2. Because it's W2+, we take away two electrons from the s energy level. The electron configuration is now [Xe] 4f^14 5d^4. If you were to draw out the orbitals, you'll find that d energy levels have five orbitals. The four electrons will...

Beatrice Petelo 1F

I am a bit confused with part d of this question:

2.45 Which elements are predicted to have the following ground-state electron configurations:
(d) [Rn]7s2 6d2

The solutions manual says that the element with that electron configuration is thorium, but isn't thorium part of the f-block?

Beatrice Petelo 1F

I find completing practice problems extremely helpful! Try to do all the hw problems and other problems in the textbook. Also, reviewing the tests and going over the problems again and your mistakes.

Beatrice Petelo 1F

Octet rule --> atoms completing their octets (noble-gas configuration) by sharing electron pairs H, He, Li, and Be are exceptions to the rule, meaning that they do not need the complete set of 8 electrons around them. Be and B commonly form compounds in which the central atom has fewer than four pai...

Beatrice Petelo 1F

The empirical formula does not work for atoms other than hydrogen and multi-electron atoms. For multi-electron atoms, we would use the other formula (the one with Zeff) because of electron shielding and repulsion caused by multiple electrons.

Beatrice Petelo 1F

Quantum number l (angular momentum) distinguishes orbitals of the given n by different shapes. Additionally, it also tells you which suborbital an electron is located in. Here are a few l-values and their corresponding letters: 0=s, 1=p, 2=d, 3=f, 4=g S orbitals have a spherical shape. P orbitals ha...

Beatrice Petelo 1F

each n: a shell each l and n: a subshell each n, l, and ml: an atomic orbital principle quantum # n: n = 1, 2, 3, etc. angular momentum l: - distinguishes orbitals of given n by different shapes - l = from 0 to (n-1) --> depends on n value - orbitals of same n and l belong to the same "subshell...

Beatrice Petelo 1F

The location (delta x) and the linear momentum (delta p) of a particle cannot be known simultaneously with arbitrary precision.
The two values are inversely proportional. If one is high, the other value is low.

Beatrice Petelo 1F

Yes, they can! Empirical formula tells you the most reduced form of elements in a compound, while the molecular formula gives you the actual number of those elements. Sometimes a molecular formula's compound can no longer be reduced.

Beatrice Petelo 1F

Is there a reason why we use two different equations for the hydrogen atom and the multi-electron model?

Beatrice Petelo 1F

Hi!
Answers on the hw and exam should always use the least number of sig figs.

Beatrice Petelo 1F

Hello! I would convert the 1 kg of CaCO3 into grams and then moles (1kg CaCO3) x (1000g/1kg) x (1mol/100.0869g -- molar mass of CaCO3) = 9.99131 which is about 10 mol CaCO3 Based on the molar ratio in the balanced equation, 1 mole of CaCO3 = 1 mole of CO2 Therefore, 10 moles of CO2 will be produced ...

Beatrice Petelo 1F

1 mole of objects means 6.0221 x 10^23 of 'objects', which in this case is carbon atoms. N=total number of objects (2.1 x 10^9) n=number of moles (unknown -- chemical amount of carbon atoms in moles) N_A= Avogadro's constant (6.0221 x 10^23) N=n x N_A --> n=N/N_A --> plug in the known values to solv...

Beatrice Petelo 1F

Hello, One important rule about significant figures is that the zeroes on the left do not count as sig figs. Terminal zeroes on the right count. For example: 8.23, 0.845, 9.00, 5.60, and 0.000123 all have three significant figures. When multiplying and dividing w/ sig figs, the answers will be in th...

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