CHEMISTRY COMMUNITY

Ashley Tran 2I

to clarify, reverse rate means the reciprocal. k'=1/k

Ashley Tran 2I

The overall reaction order will the same as the stoichiometric coefficient of the rate determining step. Otherwise, each mechanism rate will have its respective order from that step's stoichiometric coefficients.

Ashley Tran 2I

When the prompt talks about temperature, activation energy, and/or the rate constant, it is indicating the use of the Arrhenius equation.

Ashley Tran 2I

It is a way of categorizing the types of rates just like we can say the rate order of a species or overall reaction.

Ashley Tran 2I

Yes, that is correct. To clarify, this is using Le Chatelier's method.

Ashley Tran 2I

I constantly find myself having to redo problems because of silly calculator mistakes. Any tips on how I can address this?

Ashley Tran 2I

n is the number of electron transferred which can be found when you balance the redox reaction.

Ashley Tran 2I

Ecell°means standard conditions (1M, 25°C, 1atm) Ecell is at nonstandard conditions and is used in the Nernst equation.

Ashley Tran 2I

Reducing power (strength of reducing agent): species undergoes oxidation which is more likely if its standard reduction potential is more negative. Oxidizing power (strength of oxidizing): species undergoes education which is more likely if its standard reduction potential is more positive. The term...

Ashley Tran 2I

I think that is a solution manual error. It should be 2.

Ashley Tran 2I

Ecell=0 means it is a concentration cell. Enaught=0 means the cell potential is 0.

K can't be equal to 0 unless its all solids and liquids in the reaction... otherwise [p]/[r] would always be some number greater or less than 1.

Ashley Tran 2I

The solid metal is the electrode (conductor) the only exception for liquids is mercury which is a liquid when it functions as an electrode.

Ashley Tran 2I

Although we learned about Kc and Kp as separate things, K (or Q) can contain both pressure and concentration. Note, the pressure needs to be in atm or bar (since there's only a 1% difference).

Ashley Tran 2I

To do this problem you need to compare the pH and pKa... If the pH is lower than the pKa, then the compound will be protonated. If the pH is higher than the pKa, then the compound will be deprotonated. Here, since pH 6 is greater than pKa 4.75, the compound will be deprotonated will gives CH3COO- an...

Ashley Tran 2I

Based off the cell diagram, the chlorine is the cathode part of the galvanic cell so it is in the reduction part of the redox reaction.

Ashley Tran 2I

These values are given. Remember, electrode potential is the electric potential on an electrode component. In a cell, there is an electrode potential for the cathode and an electrode potential for the anode. The difference between the two electrode potentials equals the cell potential.

Ashley Tran 2I

To clarify, the cathode has a positive potential so relative to the cathode, the anode is negative.

Ashley Tran 2I

Yes, I think there is an error! That would make sense with the solutions for the half-reactions. In any case, Cl2 is both an oxidizing and reducing agent.

Ashley Tran 2I

A trick to help you remember which agent is oxidizing and which is redoing is "LEO the lion says GER"
Lose Electron Oxidize
Gain Electron Reduce

Ashley Tran 2I

This equation also relates G and G $^{\circ}$

Ashley Tran 2I

The problems with ICE tables and using the quadratic formula to solve for the equilibrium composition of a chemical reaction were also very reflective of the homework.

Ashley Tran 2I

Isothermal reversible just means the temp stayed constant so q=-w and you can use the equation nrlnv2/v1 to calculate entropy of the system.

Ashley Tran 2I

When there is no change in temperature, for example phase changes.

Ashley Tran 2I

Based on where we are in class, this has been the only relationship established. You can also think of how relative the values of ∆H and ∆S make ∆G negative at which temperatures to determine whether a reaction is spontaneous.

Ashley Tran 2I

Drawing out the Lewis structures will indicate the types of bonds. Also it may be helpful to memorize some of the organic compounds. C6H6 is benzene and has ring shape with alternating single and double carbon carbon bonds.

Ashley Tran 2I

The condition q=-w and delta U=0 comes from the process being isothermal.

Ashley Tran 2I

Yes, its on the equation and constants sheet.

Ashley Tran 2I

Yes, that's correct. The degeneracy formula is # micro-states^#particles and there are 6.026 x 10^23 particles per mole.

Ashley Tran 2I

The first part of the problem is understanding that -P $\Delta$ V=- $\Delta$ nRT so the answer should be -2.48kJ
The second part requires solving for $\Delta$ U which equals q+w
q= $\Delta$ H=-318kJ and we just solved for w since w=-P $\Delta$ V
Thus, adding q and w gives the final answer -320kJ

Ashley Tran 2I

You will need to balance the chemical equation and look at the change in moles of gas from reactants to products:

C6H6(l) + 15/2O2(g) --> 6CO2(g) + 3H2O(l)
$\Delta$ n = 6-7.5= -1.50mol

Ashley Tran 2I

Yes, during a phase change, the temperature doesn't change because the energy is channeled into breaking the intermolecular forces of the substance.

Ashley Tran 2I

Acids and bases in water are in aqueous form. However, they could react to produce a gas.

Ashley Tran 2I

Temperature rose as a result of the neutralization reaction which means heat was released which is shown by energy (q) being negative.

Ashley Tran 2I

Yes, there are two different equations
Irreversible: w=-P $\Delta$ V
Reversible (more work): w=-nRTln(V2/V1)

Ashley Tran 2I

I would use 3 sig figs because that's following the rule of using the least number of sig figs provided in the prompt. Sometimes the textbook gets the number of sig figs wrong.

Ashley Tran 2I

Pressure and enthalpy are directly proportional so as pressure increases so does enthalpy, and vice versa.

Ashley Tran 2I

Use M1V1=M2V2 such that (0.18M)(500mL)=(M2)(5mL) the M2 is the concentration of NaOH which is also the [OH-] of the original solution.

Ashley Tran 2I

It's [H3O+]/[HA] x 100 because the percent ionization is measuring how much the acid [HA] gave up protons [H3O+] the [A-] is not involved.

Ashley Tran 2I

The exception is that if Ka2 < Ka1/1000 you can treat the chemical equilibrium reaction as a monoprotic acid. This is because Ka2 is so small relative to Ka1 is has little effect on the concentration of H3O+ formed. Remember, this is because Ka represents the dissociation constant which means the ra...

Ashley Tran 2I

Chemical equilibrium problems of weak acids/bases always use an ICE table because these compounds don't fully dissociate and thus we would use the Ka/Kb value respectively to finish solving the problem.

Ashley Tran 2I

Ka and Kb represent the dissociation constant of the acid/base reaction. Thus, the high the Ka or Kb the stronger acid/base because it is more like to give/accept an H+

Ashley Tran 2I

Thee three we've covered in lecture are concentration, pressure due to change in volume, and temperature.

Ashley Tran 2I

The K value I found in Table 5G2 doesn't match the K value in the answer key so I'm having a hard time doing the problem. Can someone please verify if there's an error in the solution manual?

Ashley Tran 2I

On the class website, it says that there is a typo for this problem so in the given balanced chemical equation the coefficient in front of N2 should be 5. This would also change K in the answer.

Ashley Tran 2I

To add on, we don't include a pure liquid in an equilibrium calculation because it acts as the solvent in a chemical reaction and its change in concentration is relatively insignificant so in the K expression, the product concentration and reactant concentration would just cancel out.

Ashley Tran 2I

Set up an ICE table and fill in the info you are given by reading the initial and equilibrium partial pressures of each compound. Then you can work out the change amount. From there, to write the chemical equation, determine if there is a ratio between the amount of change of A and the amount of cha...

Ashley Tran 2I

K represents the ratio of equilibrium concentrations of products to reactants so when both the concentration of the products and reactants change proportionally (due to change in pressure due to change in volume), K remains the same.

Ashley Tran 2I

Yes, the states will be given because we need to know the states of the chemical compounds in a reaction in order to write a K/Q expression.

Ashley Tran 2I

To clarify for both Q (initial conditions) and K (equilibrium conditions): when the compounds are gases use P for partial pressure and when the compounds are in aqueous state use the concentration (brackets). Disregard compounds in solid or liquid phase. Don't use partial pressure and concentration ...

Ashley Tran 2I

Water as liquid is a solvent: not included in equilibrium constant because we assume there is a significantly large amount of solvent so that the amount starting (reactant) and amount ending (product) are essentially the same. When we put this in the equilibrium constant equation set up, the numbers...

Ashley Tran 2I

Yes, there's a list. You can google it, but here's the one I use.

Ashley Tran 2I

Hemoglobin is four myoglobins. It binds to 4 oxygen molecules and transports the O2. Therefore, it is a polydentate ligand. I don't believe it is chelating.

Ashley Tran 2I

You can tell if something is a polyphonic acid if it has more than one H+ cation. For example H2S,H2SO4,H3PO4. Polyphonic bases can accept more than one proton. It can be recognized by compounds with cations of a greater than +1 charge. This is because OH- is -1 so if the cation is more than +1 we n...

Ashley Tran 2I

How would you do it for ammonia and phosphoric acid? We knew the ionic compound created would be ammonium phosphate. Since ammonium is +1 and phosphate is 3- we need three NH4+ to balance out the PO4 3- From there, work backwards to write the reactants side of the chemical reaction. 3NH3(aq) + H3PO...

Ashley Tran 2I

In this exercise, parts e and f what does it mean by Al(H2O)6 3+ (aq) and Cu(H2O)6 2+ (aq)?

What is the significance of writing both H2O and (aq)?

Ashley Tran 2I

I noticed both of these chemical formulas being written for coordination complexes. Is one more correct than the other? How do we know which one to use? An example is 9C3 parts c and d.

Ashley Tran 2I

Ferrate is the Latin name. We use it to indicate that the coordination complex ion has an overall negative charge. Some other common ones we discussed in discussion are

copper: cuprate
gold: aurate
lead: plumbate

Ashley Tran 2I

To add on, you can tell if the reaction involves a weak/strong acid/base by checking if there is a single/double equilibrium arrow.

Ashley Tran 2I

Yes, "poly" just means more than 1. In lecture we specified the number of bonds using other prefixes (bi/tri/tetra) but polydentate works for all of them.

Ashley Tran 2I

I'm not sure if we need to know it, but to my knowledge you just count the radical as another thing around the central atom so it increases the coordination number by 1.

Ashley Tran 2I

Jorge Ramirez_4H wrote:Why is co2 non polar? isn't based on electronegativity?

CO2 is non polar because the dipoles cancel out. The difference in electronegativity between C and O are in equal magnitude and opposite direction.

Ashley Tran 2I

Ion-dipole is stronger that hydrogen bonding because it has an ion. Think of hydrogen bonding as a special (and stronger) type of dipole-dipole intermolecular force.

Ashley Tran 2I

higher polarizing power --> greater dipole-dipole forces --> stronger intermolecular forces --> higher melting point

Ashley Tran 2I

Technically, every compound could have a resonance structure then. When we draw Lewis structures, we pick the most realistic/stable structure such that there are few formal charges. In the case of SO2, there would be 2 sigma and 2 pi bonds because sulfur forms two double bonds, one with each oxygen.

Ashley Tran 2I

Dipole-dipole interactions occur anywhere there is a covalent bond and difference in electronegativity (basically anytime two different elements form a covalent bond). A dipole moment is when there is a NET dipole-dipole interaction. This occurs if the dipole-dipole interactions don't cancel out. In...

Ashley Tran 2I

Also, check the octet rule to see if the central atom can hold more than 8 e- (whether those be lone pairs and/or bonds).

Ashley Tran 2I

Yes, the repulsion of a lone pair pushes the atoms bonded to the central atom closer together. This is because the electron cloud of a lone pair can spread over a larger volume than a bonding pair can, because a bonding pair (or several bonding pairs in a multiple bond) is held in place by two atoms...

Ashley Tran 2I

I found this video very useful! https://www.youtube.com/watch?v=GnXSGR-UEDI

Ashley Tran 2I

For this problem, I found it useful to look at the bond angles. The first example, bent, has angles 120 degrees and we know that for a bent electron arrangement, there must be 2 bonding pairs and 1 or 2 lone pairs. Therefore, in the diagram, when only 2 bonding pairs are shown, we know we must have ...

Ashley Tran 2I

Drawing the Lewis structure can help you count up the total lone pairs and the total bonding pairs on a central atom which then correlates to the molecular shape and electron arrangement of a molecule. Remember, however, that you must be able to draw the most correct Lewis structure for this method ...

Ashley Tran 2I

How are intermolecular forces different from chemical bonds?

Ashley Tran 2I

A good tip to have in mind is carbon generally only has London dispersion intermolecular forces. This is due to the symmetry it creates from the bonds it forms with other elements (carbon is tetravalent). However, in addition to that, there could be other intermolecular forces among the other elemen...

Ashley Tran 2I

A quick tip to always keep in mind is hydrogen is a nonmetal so when you see HCl/HBr/HI it's tempting to say it's an ionic bond because H has a +1 charge and halogens have a -1 charge and they're on opposite sides of the periodic table like most ionic compounds. However, that'd be incorrect, these c...

Ashley Tran 2I

The info sheet online says pen!

Ashley Tran 2I

1. Tally up total of valence electrons in compound. 2. Choose which element goes in the middle. It's usually the one that shows up the least in the chemical formula and/or it is the least electronegative. 3. Draw single bonds from central atom to the atoms you have remaining. Add lone pairs to satis...

Ashley Tran 2I

Why is CO more polar than BO? This was on a workshop review worksheet.

Ashley Tran 2I

A) The equations you need to use is E=-hR/n^2 and deltaE=Efinal-Einitial then you can relate E to frequency using the equation E=hv.

B) deltaE will be negative. To fall energy levels, energy is being emitted. Energy of the photon, however, will be positive (it can never be negative).

Ashley Tran 2I

Micah3J wrote:Will we need to know the f block for the midterm?

No, we need to know s, p, and d.

Ashley Tran 2I

In lecture and discussion, we've been saying one orbital has higher/lower energy than another orbital. I understand we can tell by looking at n, the principal quantum number. However, what does the energy of an orbital actually mean?

Ashley Tran 2I

An easy trick to remember is to count the groups across the period table, disregarding the transition metals, the order is +1,+2,+3 the 4th group is "neutral" then -3,-2,-1, noble gases don't form ions.

Ashley Tran 2I

Here is what's posted online:

Midterm is 2 hours, 8 questions.
Midterm covers all material up to the end of Focus 2D in Outline 3:
Chemical Bonds.
Questions will come from the Homework and Online Assessments.

Ashley Tran 2I

Yes, I believe what you stated is corrected. Basically, my TA explained that starting with elements in the 3rd row, though they don't have electrons on the d orbital, they have access to the 3d subshell which is how the additional electrons after the 8th are getting stored there.

Ashley Tran 2I

Why is the electron configuration of tungsten [Xe] 4f14 5d4 6s2 instead of [Xe] 4f14 5d5 6s1? I thought we were supposed to follow the rule about d5 and d10 so that there was at least one electron in each d orbital to make the atom more stable?

Ashley Tran 2I

What is the format of the midterm exam? (How many questions?/is it multiple choice/free response?) Thanks!

Ashley Tran 2I

Why are H, He, Li, and Be exceptions for the octet rule?

Ashley Tran 2I

Please help me answer the question in the photo attached. Thanks!

Ashley Tran 2I

The textbook answer is in increasing n (principal quantum number) for bismuth [Xe] 4f14 5d10 6s2 6p3. Which is the convention in my experience. Dr. Lavelle might have been explaining how to write electron configurations in increasing energy to understand which orbitals get filled first with electron...

Ashley Tran 2I

As we go across a period, the atomic radius decreases so there is a greater attraction between the negatively charged electrons and positively-charged nucleus thus it will take more energy to remove a valence electron (greater ionization energy).

Ashley Tran 2I

We will not need to draw the orbitals. Planes refers to the axes the orbitals can be oriented. This shows how for s we can only have 1 (one orientation for a spherical shape) so one orbital in 2 subshell. While p we have three (xy/xz/yz) so there are 3 orbitals in the p subshell. And the patterns co...

Ashley Tran 2I

How many orbitals can have the following quantum numbers in an atom: (a)n=2,l=1;(b)n=4,l=2,ml=-2; (c)n=2;(d)n=3,l=2,ml=-1?

Ashley Tran 2I

How many orbitals are present in the (a) 4p-subshell; (b) 3d-subshell; (c) 1s-subshell; (d) 4f-subshell of an atom?

Ashley Tran 2I

How are wave functions/orbitals connected to quantum numbers? I'm confused... isn't the wave function about the whole atom and the quantum number refers to individual electrons?

Ashley Tran 2I

We won't really be using the Heisenberg Indeterminacy Equation to do calculations. It is rather to explain that electron(s) can't be located inside the nucleus of an atom, there is a physical limit to the minimum size that atoms can exist, and furthermore, that electrons must have wavelike propertie...

Ashley Tran 2I

Find energy per photon using the equation E=hc/ $\Lambda$

Multiply by 64 because there are 32 Watts per second and the prompt asks for 2 seconds (1 W = 1 J/s)

You will get 1.4 x 10^20 photons, then convert to moles using Avogadro's number.

The final answer will be 2.3 x 10^-4 mol photons

Ashley Tran 2I

The de Broglie wavelength equation relates h to p and p is equal to mass times velocity. Therefore you can substitute p (momentum) for the mass of the proton/neutron and the velocity is the same for either particle (as given in the prompt). h is Planck's constant.

Ashley Tran 2I

As McKenna mentioned, the concept isn't a big thing to stress over understanding. The main point of today's lecture is for us to know that orbitals aren't just shapes drawn when talking about electrons or stating what the electron is s/p/d/etc. as we might have in high school. They are actually math...

Ashley Tran 2I

In the textbook there is a small paragraph that says in the UV region of the spectrum, n1 is equal to 1. From there you can solve for n2.

Ashley Tran 2I

The Rydberg equation is sometimes hard for us to tell which level should be n1 and which should be n2. The method we learned in lecture is based off our understanding of the conservation of energy so that the change in energy is always E final - E initial and E=-hR/n^2 and we can tell if the change ...

Ashley Tran 2I

The energy needed to remove an e- is known as the ionization energy. It varies depending on the properties of the atom, or in this case the properties of the metal surface. Typically we are given components of the problem that we can use to solve for the unknown. For example, we are given the freque...

Ashley Tran 2I

The work function from what we've been introduced to in lecture shows the minimum energy required to eject an electron from a metal surface. It also shows a relationship between the energy of the incoming photon and the kinetic energy of the e- since it is the difference between the energy of the in...

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