CHEMISTRY COMMUNITY

Arya_Naeim_1H

It's the number of orientations a molecule can have. You can draw the molecule to see how many positions the milecules can have and put it to the power of the number of atoms in a molecule. Usually as T goes to 0 K atoms go to a crystal state.

Arya_Naeim_1H

Yes the sign flips when you reverse the reaction.

Arya_Naeim_1H

I don’t think we need to get too much in the geometry for this class but Dr. Lavelle did say that the orientation of the molecules affects how much they collide and this is seen by the frequency factor A that is in our kinetics equations.

Arya_Naeim_1H

Look at the appendix for Eº cell values based on the reactions. For example Cu would be Cu2+ + 2e---> Cu (s) Eº= what the appendix says. Then reactions that are most negative would be the element has the strongest reducing strength.

Arya_Naeim_1H

Kinetic control is when the product is formed by the fastes reaction. The question is does kinetic control predominate at higher or lower temperatures. In class today we determined that as temperature increases the rate of the reaction increases so I know that kinetic control predominates at higher ...

Arya_Naeim_1H

When comparing elements for which has the most reducing power we look at the standard reduction potential based on the half reaction. However, some elements like Fe have two reactions Fe2+ +2e- --> Fe and Fe3+ + 3e- --> Fe and both reactions have a different potential. Which one do I use for Fe when...

Arya_Naeim_1H

If the value of -nFE is negative then the cell does work. If -nFE value is positive then work is being done on the cell.

Arya_Naeim_1H

When picking the right half reactions to use from the appendix in the back of the book, the more accurate ones tend to be the ones that relate best to the equation at hand. Given that MnO4- is what is used the first half reaction I would try to find would include MnO4-. Once you add up the half reac...

Arya_Naeim_1H

I asked Dr. Lavelle about this and he said that KOH was the textbook specifying the base that was used but that the question would generally give us more information if we needed to write down the base in the cell diagram.

Arya_Naeim_1H

Text book probelm 6N 7b gives the following cell diagram Pt(s)| H2 (g, 1.0 bar)| H+ (aq, pH= 4.0) || H+ (aq, pH=3.0) | H2 (g, 1 bar) | Pt(s). My assumption is that the two half reactions are 2H+ (0.001)+ 2e- ---> H2 and H2---> 2H+ (0.0001)+ 2e-, which in this case n=2. However the textbook solutions...

Arya_Naeim_1H

Entropy is the amount of disorder in a system and internal energy is the total eenrgy the system has. internal energy= heat+ work and entropy of a system generally is Heat/temperature.

Arya_Naeim_1H

A comma is used when elements are in the same phase so if the cathode has two substances that are aqueous for example, then you would only need a comma. If substances in the cathode are different a "|" would be used to separate the two. Platinum is a metal conductor that is generally used ...

Arya_Naeim_1H

What you have listed is the correct answer, make sure that you are using subscripts and the correct arrow sign provided by achieve. The way to do this would be to list the reactqnts Fe+O2+H2O-->Fe2O3*H2O and balance iron, hydrigen, and oxygen atoms like you would do in a normal reaction and add coef...

Arya_Naeim_1H

Yeah Faraday's constant does not change as its units are C/mol and therefore it is not dependent on anything.

Arya_Naeim_1H

The formula for isothermal is always w= -nRTln(v2/v1).However for isothermal free expansion there is no work done. So Delta U=q. Q is the same in both free expansion and reversible expansion because thta is unrelated to work but the work will be different.

Arya_Naeim_1H

I think it really depends what information you are given and what the question is asking. If the question wants something in J/K then make sure moles cancel out. If the question wants J/(gK) then you don't need moles or grams to multiply anything by.

Arya_Naeim_1H

Yes if Delta S of the systems and the surrouningds is also zero then the system is at equilibirum.

Arya_Naeim_1H

Q=mc*delta T
For constrant pressure q=H
Therefore you find enthalpy and the equation becomes H=mc*Delta T
Then you can solve for Delta T.

Arya_Naeim_1H

Biological systems need to function need to function so they are highly ordered. However if there has been evidence that diseases like Alzheimers have been linked to entropy in the body. Since the boyd is an open system energy can flow in and out and the body is therefore good at managing entropy an...

Arya_Naeim_1H

How can you tell from chemical reactions if the entropy increases or decreases?

Arya_Naeim_1H

The seocnd law of thermodyanmics says that the entropy of an total isolated system cannot decrease but it's different for a non-isolated system. For exmaple in a fridge the food inside the fridge gets cooler so its entropy decreases, but the heat is released outside and therefroe outside the frideg ...

Arya_Naeim_1H

Why do polymers have less entropy than monomers? I thought since polymrs are larger they should have less entropy?

Arya_Naeim_1H

In this process W= -p*delta V E internal is generally for most gases 1.5 nR*T If presssure is always constant but the gas expands that means that volume is increasing. Based on PV= nRT, if Volume increases temperature also has to increase and if temperature increase the Internal energy will increase...

Arya_Naeim_1H

Internal energy= q+w.

Given that all energy in a system is conserved it can either be in terms of heat or work. Even if the internal energy of a system is zero like in an isothermal proces, there is still heat and work in the system they just cancel each other out.

Arya_Naeim_1H

If you are talking about the equaltions w= -nRT (v2/v1) vs w= -P*delta V eequations then you use the -nRT equation if temperature is constant and pressure is changing really slowly and the -p*delta V equation if pressure is constant.

Arya_Naeim_1H

Okay so you are given n=0.513 mols, R= 8.3 J/K mol (constant) T1= 298 K and T2= 298+15.5 K and P= 1.00 atm which is about 1.00*10^5 Pa (the SI units) PV= nRT V= nRT/P Solve for V1 and V2 using T1 and T2. Work= -p*(V2-V1) Change in internal energy Energy= 1.5 nR*Delta T Change Internal energy= W+q Q=...

Arya_Naeim_1H

It depends what problem you are doing and what the other units are. But generally speaking you would want things in mols and that is the right conversion.

Arya_Naeim_1H

That is based on coordination compounds which was from 14A. I asked this similar question after class and it seems like if there's an equation dealing with coordination compounds we'd be given more information since coordination compounds are not part of 14B.

Arya_Naeim_1H

It really depends on what is given and what units you use for constants. I would suggest writing all the units out when doing a problem to see what cancels out. I will say that if you are using SI units and use Kevlin for temperature m^3 for volume and Pascals for pressure, you can generally get ans...

Arya_Naeim_1H

pH less than 7 is acidic and greater than 7 is basic. 10^-8 to 10^-14 is basic and 10^-1 to 10^-6 is acidic.

Arya_Naeim_1H

You just have to know if the molecule is making H3O+ in which case Ka is used or OH- in which case Kb is used. You're generally given Ka but you may need to convert to Kb if the reaction is different.

Arya_Naeim_1H

When looking at the graph, If products are higher than reactants its endothermic and if products are lower than rectants the reaction is exothermic.

Arya_Naeim_1H

I think it has to do with the fact that there is more energy needed to vaporize and turn all the liquid into gas than just melting solids into liquids. A lot more heat and more time is going to be needed to finish converting all the liquid into gas.

Arya_Naeim_1H

NaCl

NaOH is a strongh base
HCl is a strong acid so NaCl is netural.

Basically if the cation is from a strong base and anion part of storng acid= neutral
Cation from weak base, anion from strong acid= strong acid
cation from strong base, anion from weak acid= strong base

Arya_Naeim_1H

H3O+ and Clo2- both get around 0.6 M at equilibrum. Therefore HClO2 loses about 0.06 from its initial 0.1 M.
KA= (0.06*0.06)/(0.1-0.06)= 0.09
pkA= -log(KA)= -log(0.09)=1

Arya_Naeim_1H

A) HCL is the only strong acid and therefore it's pH should be the least but you can calculate it mathematically using the formuak pH= -log(H+) B) The conjuage acid of the molecule is CH3Nh2 with a pKB given of 3.44. You can use the rule pKB+pkA=14 to find pKA and from there find KA. KA= 2.8*10^-11 ...

Arya_Naeim_1H

You should always balance the equation if it's unbalanced. Normally to find K at least one the equilibrium concentration will be given. An increase in temperature means a higher K for a endothermic reaction and a smaller K for an exothermic reaction.

Arya_Naeim_1H

It depends on the molecule given but you would set up an equilibrium equartion Ka= [Reactants]/[Producrs] and find the equilibrium concentration of the missing value. The percent ionziation is then (H+)/(concentration) *100 (assuming this is an acidic reaction)

Arya_Naeim_1H

Le Chatelier's principle describes that system wants to be at equilibirum and if there is a change the system will shift to counteract the change. However in an equilibrium reaction there does not have to be an equal concentrations of reactants and products. If a reaction is already producing produc...

Arya_Naeim_1H

I know a Le Chateleier's principle explains how a reaction shifts, but what factors are used to determine how fast or slow a reaction and length of time it takes for a reaction to reach equilibrium?

Arya_Naeim_1H

I have not fully looked at this topic yet but based on equilibirum if you have the equation H+ + A- -->-<- HA

Then the equilibrium table would have a -x for the reactants (H+ and A-) and a +x for the HA (as it is a product).

Arya_Naeim_1H

The threshold is less than 10^-3. X is not considered zero but x is so small that the concentrations present in the reaction would not change. For example if a rectant was present at 0.5 M before equilibrium it would still be about 0.5 M during equilibrium.

Arya_Naeim_1H

When solving for concentrations you use mols/Liter, when solving problems with pressure is it bars/liter or just bars?

Arya_Naeim_1H

In class today Dr. Lavelle mentioned that when doing an ice table if K is smaller than 10^-3 then we can assume that the initial concentrations of reactants do not change. On the audio visual module it said to use the something when 10^-4 so would something like 0.9*10^-3 count as something small en...

Arya_Naeim_1H

The concentrations of solids do not change in an equilibriun reaction.

Arya_Naeim_1H

You basically want to figure out a way to rearrnage the equations 2 and 3 (the ones where Kc is given) so that the sum of them is equation 1 (where no Kc is given). When you add two equations together you multiply the Kcs of those you equations. Equation 1= 2NH3+3 I2--> 6 HI + N2 I notice that there...

Arya_Naeim_1H

I do not think combustion reactions can reach equilibrium because I do not think that combustion reactions are considered reversible reactions and if there is no reverse reaction then there can't be equilibrium.

Arya_Naeim_1H

A UA worksheet stated that C10H22 has a higher boiling point than water because it was larger. However I thought H2O has a high boiling point due to hydorgen bonds. Can someone explain the answer?

Arya_Naeim_1H

I was looking at a UA worksheet that said that Mg2+ has a higher polarizing power than Li+. I know that more highly charged cations have a higher polarizing power but Li+ is one row above Mg2+ so I would assume Li+ is smaller. Can someone explain which one has the higher polarizing power and why?

Arya_Naeim_1H

Gabriel nitro's chemistyr practice final had a question "which of the following species has the lowest coordination number and lowest number of ligands" the diagrams show cisplatin, carboplatin, oxaliplatin, satraplatnin, [Pt(Cl)2en], and transplatin. Can someone explain why the answer is ...

Arya_Naeim_1H

Oxidation number is the charge of the cation in a coordination compound. You can solve for it by adding up all the charges of ions and molecules in the coordination compound and making sure everything adds up to zero.

Arya_Naeim_1H

Given [H+]= 5.1*10^-12
pH= -log(5.1*10^-12)= 11.29
POH+PH= 14
POH= 14-pH= 14-11.29=2.7

-log(OH)= pOH
log(OH)= -pOH
OH= 10^-pOH= 10^-2.7= 0.001

Arya_Naeim_1H

Can someone explain why SO3 and B(OH)3 are both considered lewis acids. I'm having a hard time visualizing it?

Arya_Naeim_1H

I personally just memorized that sp means the electron geometry is linear, sp^2 means it is trigonal planar, sp^3 means tetrahedra, sp^3d means trigonal bipyramidal, and sp^3d^2 means octahedral. If I said what is the geometry bond angle and hybridization of CO2, I would know that after draiwng the ...

Arya_Naeim_1H

I would name this hexacyanocolbate(III). There are 6 cyanide anions and cyanide becomes cyano. The complex also has a negative charge so Colbat becomes colbate. Lastly CN has a X-6=-3 X=3, and therefore Colbat's oxidation number is 3.

Arya_Naeim_1H

I did not use the answer tri in the week 1 achieve questions. You would only use tri if there were 3 NH3 compounds given in the homework.

Arya_Naeim_1H

If the radius of one atom is 144pm, then the length from the center of one AG atom to the center of another AG is 144*2=288 pm which is why it is used in the problem.

Arya_Naeim_1H

The steric number can help determine the shape of a molecule which then helps identify the bond angle. However the steric number does not take into account how lone pairs affecrs so the steric number only takes the electron gemonetry into account. If the sgteric number is 2 there is a 180 degree ang...

Arya_Naeim_1H

When there is covalent bonding, the orbitals of electrons sharing the bonds have to be the same. Therefore the s and p orbitals of a cventral atom can combine to form a hybrid bond. Whenever covalent bonding occurs, there will be the hybirdization of orbitals. SP if the regions of electron density a...

Arya_Naeim_1H

Knowing the shape methane is CH4 so there are four regions of electron density meaning just looking at how the electrons are configured the shape is tetrahedral which is an sp^3 hybrid orbital. Carbon is bonding to four hydrogen so it would be 4sp^3. Looking at electron configurations, carbon is [He...

Arya_Naeim_1H

In class we learned that linear is 2sp with 1s+1p= 2sp. I understand the concept in terms of the number of atomic orbitals= number of hybiridized orbitals but for linear compounds specifically I have a hard time seeing it in terms of electron configurations. If I have one s there would be two arrows...

Arya_Naeim_1H

There has to be dipole moments in a molecule where the uneven sharing of electorns in a molecule occur. Additionally, the net dipoles cannot cancel out. In CF4, even though F is more electrongeative leading to the uneven sharing of electrons the tetrahedral shape of CF4 leads to the dipole moments c...

Arya_Naeim_1H

Polarzability is a measure of how much an electron cloud can be distorted and is used to describe anions. Larger anions with high charges have a higher polarizability which creates alrger dispersion forces. Polarizing power descirbes the ability of cations to polarize anions. Small highly charged ca...

Arya_Naeim_1H

The steric number is the how many atoms the central atom is bonded to+ number of lone pairs. If the steric number is 2 the hybirization is sp, if it's 3, the hybirixation is sp^2 and if it's 4 the hybirizaiton is sp^3.

Arya_Naeim_1H

I think he's going over it in class this week but from what I remember I think you look at how many atoms the central atom is bonded to+ number of lone pairs in what is called a steric number. If the steric number is 2 the hybirization is sp, if it's 3, the hybirixation is sp^2 and if it's 4 the hyb...

Arya_Naeim_1H

I think that oxidation charge is very similar to ionic charges. Halogens have a -1 charge, oxygen generally has a charge of 2-, ions in the first column of the periodic table have a +1 chaerge and ions in the second block of the perioc table of a +2 charge.

Arya_Naeim_1H

The electron configuration of Ga is [Ar]3d^10 4s^2 4p^1. In Ga3+ we take away the 3 outer electrons in the shell n=4. Therefore the 4p^1 and the 4s^2 electrons are taken away making the electron configuration [Ar] 3d^10. The electron configuration of Ti is [Xe] 4f^14 5d^10 6s^2 6p^1. In Ti 3+ we tak...

Arya_Naeim_1H

This confused me too but I think the rule is that for acids you bond the H to the O as a general rule. This is true of many acids and not just chloric acid.

Arya_Naeim_1H

I think since both elements have dipole-dipole forces you then have to look at the polarizability of the elements and in CHI3 I is larger and therefore has more polarizability meaning that CHI3 has stronger intermolecular forces and therefore a higher melting point.

Arya_Naeim_1H

Can someone explain why when molecules are lined up in the same direction there intermolecular dipole-dipole forces are stronger than if the molecules are not alligned?

Arya_Naeim_1H

If the the vectors cancel out they are seen as non polar and therefore would not have have dipole-dipole intermolecular forces. Those molecules would only use london dispersion forces as their intermolecular attraction.

Arya_Naeim_1H

When moleucles have seprated formal charges that are high, they are considered more unstable. When moleucles are less stable they are high in energy.

Arya_Naeim_1H

I think because sulfur is in period 3 of the period table n=3, and we know from quantum numbers that when n=3 elements can hve s oritbals, p orbitals and d orbitals. Sulfur does not use d orbitals but because it has them it can use them to accept electrons making it an acid.

Arya_Naeim_1H

The Lewis structure of Carbon Monoxide is :C triple bond O:

This creates a formal charge of C to be -1, and a formal charge of O to be +1. However shouldn't the formal charge of O be more negative than the formal charge of Carbon. How is this possible?

Arya_Naeim_1H

One of the textbook problems asked for a Lewis structure of H2C(NH2) COOH. I saw the answer in the texbook but I had trouble figuring it out on my own. Can someone walk through the steps of how they would approach this question to get the Lewis structure?

Arya_Naeim_1H

I think the amount of electrons an element will lose can be found by the element it is bonded too. Fe can have a +2 charge or a +3 charge. In FeCl3, we know that there is Fe with some charge and that each Cl molecule has a -1 charge. Cl3 therefore has a charge of 3-. To counter the 3- charge Fe must...

Arya_Naeim_1H

You are on the right track with the Carbon being double bonded with one oxygen and a single bond with the other two oxygens. The formal charge of Carbon is then 4 ve- 4 bonds= 0 formal charge. The two single bonded oxygens would have a formal charge of 6-(1+6)= -1 and the oxygen with the two bonds w...

Arya_Naeim_1H

I kniow we can use the molar mass to convert grams to mols. However how do you use the molar mass to find the grams of an atom?

Arya_Naeim_1H

In class Dr. Lavelle showed Lewis structures for (NH4)2 So4 and drew NH4+ and So42- seprately. If they are combined in the same molecule is there are way to bind NH4+ to So42- and if so how would that be done.

Arya_Naeim_1H

I want to clairfy something. The general rule is that: If you find that an electron has a d^4 or a d^9, then it becomes either a d^5 or a d^10 with the s^2 becoming an s^1.

Arya_Naeim_1H

The three p-orbitals are px, py, and pz. The electron configuration for F is 1s^2 2s^2 2p^5. F- has another electron so it is 1s^2 2s^2 2p^6. However, if you want to break it up into subsets F would be 1s^2 2s^2 2px^2 2py^2 2pz^1. In this case you show which electrons go into which subset of p. The ...

Arya_Naeim_1H

It's shorthand for the electron configuration. The last noble gas before Calcium and Scandium is Argon. Argon's electron configrauation is 1s^2 2s^2 2p^6 3s^2 3p^6. Calcium's electron configuration is 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 and Scandium's electron configuration is 1s^2 2s^2 2p^6 3s^2 3p^6 3d^...

Arya_Naeim_1H

Based on Dr. Lavelle's lecture it seems like we only need to know the elements with 3D and not 4D. In the 3D row the only exceptions would be chromium and copper (they have the electron configuration of 3d^5 and 3d^10 which is why they have a 4s^1). However silver would also have a 5s^1 given that i...

Arya_Naeim_1H

Is it possible to answer a question like: If a ball has a mass of 7 kg and a velocity of 2 m/s find the frequency.

I know DeBroglie's equation can find the wavelength. Howver is there any way to convert wavelentgh to frequency if we are not talking about light? Or can we only find the wavelength?

Arya_Naeim_1H

The texbook described how Einstein's theories related to the photoelectric effect. The third one was the kinetic energy of the electron ejected from the metal increases linearly with the frequency of incident radiation. I had trouble understanding what the statement means. Can someone explain what t...

Arya_Naeim_1H

In Friday's lecture, after Professor Lavelle did the DeBroglie equation example he showed two images of atoms, one with waves that have an allowed energy level and one with waves that do not have an allowed energy level. Can someone explain what in the wave models shown would allow there to be an en...

Arya_Naeim_1H

lamba= h/(p)
lambda= h/(mv)
lamba*mass*velocity= h
mass= h/(lambda*v)
lambda is the wavelength

Arya_Naeim_1H

In question 23 of section 1B of the textbook we are asked to use the uncertainity equation to find velocity with all the other numbers in the Heisberg uncertainity equation given. The calculations for how velcoity is found made sense. However I thought the Heisenberg equation used delta v. Is the ve...

Arya_Naeim_1H

The conceptual answer is that you cannot have a negative frequency for a wave so frequency is always going to be positive. Therefore no negative sign will be used. Even if your mathematical theory is correct you will always have a positive frequency which would explain why there is no negative sign ...

Arya_Naeim_1H

The EM is a spectrum and different types of light are dependent on their wavlenght and frequency (for example UV lihght has a lower wavelenght and higher frequency then visible light). The EM spectrum shows which types of light have higher frequencies then others and it also shows the wavelength of ...

Arya_Naeim_1H

When it comes to solving problems involving light and electrons, I first like to write the information given and then I like to write the information I am trying to find. From there, I generally look at the formula sheet Dr. Lavelle has on his website and see if any of his formulas work towards solv...

Arya_Naeim_1H

The fact that light and electrons can act as both waves and as particles explains how we came up with various equations and models for light and electrons. It basically explains that for each experiment it may either act as light and as electrons. All the equations we learn assume that electrons and...

Arya_Naeim_1H

1000 mmols= 1 mol. Convert the grams of sodium carbonate to mols and then multiply that by volume in liters.You should then find the concentration of Na2Co3 M= n/V. Volume is found by V= n (mols)/M (mols/liter). Use the forumula of sodium cabrodnate to see how many mols of each element there is in o...

Arya_Naeim_1H

The formula unit I think is the basic unit of the compound. That would explain why the avogadros number is used to convert mols to formula units in those problems. For example the number of formula units of KFNO3 as seen in E25 (a) would be the number of KFNO3 molecules present.

Arya_Naeim_1H

Let's say for some reason in the equation 2h+O--> H2O, H is the limiting reactant. There are 0.50397 grams of H (0.5 mols) and 12 grams of O (0.75 mols). How would you find the moles of O used and H2O produced. In the examples in class we mainly had the limiting reactant be the one without a coeffic...

Arya_Naeim_1H

Let's say I am trying to find the molar mass of CaF2 in order to do a more advanced calculation. Ca= 40.078 grams/mol, F=18.9984032 grams/mol. The molar mass of CaF2 would be 78.0748064. However, if finding the molar mass was just one step in a more complex problem would I keep the answer 18.9984032...

Search found 96 matches