CHEMISTRY COMMUNITY

Ariana Iranmahboub1G

It comes from deltaU=w+q which is the same as deltaU=deltaH-P*deltaV. You can rearrange this to be deltaH = deltaU+P*deltaV.

Ariana Iranmahboub1G

It would depend on the reaction order. For instance, if it is zero order the unit is mol*L^-1*s^-1. For the first order, it is s^-1. And for the second order, it is L*mol^-1*s^-1

Ariana Iranmahboub1G

I believe so, yes.

Ariana Iranmahboub1G

I am unsure of how we use the steady state approach for reaction mechanisms. Can someone please explain step by step how to use this approach?

Ariana Iranmahboub1G

One way would be to find the enthalpy of formation for each molecule and subtract the net enthalpy of formation of the products by the net enthalpy of formation of the reactants.

Ariana Iranmahboub1G

Yes the slowest step would be the rate determining step.

Ariana Iranmahboub1G

In a concentration cell, the two half-cells have the same electrodes. However, the concentrations in each half-cell is different. As the cell reaches equilibrium, electrons from the cell with the lower concentration are transferred to the cell with the higher concentration, creating a voltage. When ...

Ariana Iranmahboub1G

I believe the unique average rate is just the more preferred formate for the average rate which is the average rate of the species divided by its stoichiometric coefficients. This is more preferred because it would be the same for all reactants and products in the reaction.

Ariana Iranmahboub1G

For a zero order reaction, the rate is equal to k, so it is independent from [A]. For this reason, why we plot [A] over time, the graph is linear with a slop of negative k.

Ariana Iranmahboub1G

I think they use K prime for the rate of the reverse reaction to differentiate it from the rate of the forward reaction.

Ariana Iranmahboub1G

Molecularity is the number of species in an elementary step. The rate law for each elementary steps follows its molecularly. For instance, the molecularity of a rate =k[A] is unimolecular and for the rate k=[A]^2 or k[A][B] is bimolecular.

Ariana Iranmahboub1G

Since we use the integrated rate law to compare the rate function over time, when we solve for the 1st order integrated rate law, the rate = k[A] so the the initial concentrations cancel out, leaving the half-life equal to 0.693/k. On the other hand, since the rate for 2nd order is k[A]^2, when we s...

Ariana Iranmahboub1G

A straight line plot of the natural log of reactants vs. time would imply that the reaction is at first order.

Ariana Iranmahboub1G

I remember Dr. Lavelle said that it was more preferred in chemistry to write the general statement in that formula. I believe it results in the same formula (unique rate) for all concentration of reactants and products.

Ariana Iranmahboub1G

I believe for both you can solve for the standard cell potential by subtracting the standard cell potential of the cathode by the standard cell potential of the anode. I believe another way to calculate standard cell potential is to divide the standard delta G by -nF.If the standard cell potential i...

Ariana Iranmahboub1G

In galvanic cells, electrons do only flow in one direction. The salt bridge is used to allow ion transfer in order for two solutions to remain neutral, so I don't think electrons can flow both ways.

Ariana Iranmahboub1G

We do not include H20 in the cell diagram because water is a solvent. Since there are already aqueous solutions, which is a solute diluted in water, in a cell diagram, it would be redundant to add water to the cell diagram.

Ariana Iranmahboub1G

I don't know if it is better to have less reactants than products when applying the Nernst equation, but I do know that when there is less reactants and more products, the nonstandard cell potential is less than the standard cell potential. On the other hand, if there is more reactants and less prod...

Ariana Iranmahboub1G

If we are using the standard hydrogen electrode, then it is a 1M solution or 1 atm at 25 degrees Celsius?

Ariana Iranmahboub1G

Hydrogen is a standard electrode because it standard electoral potential is zero, which is why its used as a reference for electrical potential measurements.

Ariana Iranmahboub1G

You use platinum as an electrode to transfer electrons if the half-reaction has no conducting solids in both the reactants and product.

Ariana Iranmahboub1G

I believe that equation is only pertained for change in entropy. Entropy does increase with temperature, but the higher the temperature, a certain amount of heat added to a system will cause a smaller change in entropy.

Ariana Iranmahboub1G

Potential Difference is work over charge. Voltage would be an example of potential difference.

Ariana Iranmahboub1G

If there is one line, then that represents an interface between phases that are in contact with each other such as a porous disc or wall. If there is two lines, then that represents a salt bridge.

Ariana Iranmahboub1G

Why is the gibbs free equation at equilibrium (delatG= -RTInK) an extremely useful equation?

Ariana Iranmahboub1G

I believe it would depend on what the problem is asking. If the problem want to know ow far away it is from equilibrium, we would want to use G = G* +RTlnQ to find Q. On the other hand, if the problem wants to understand gibbs free energy at equilibrium, we would want to use G= - RTlnK.

Ariana Iranmahboub1G

If the substance reaches its boiling point, melting point, or freezing point, that makes it clear the substance undergoes a phase change. In other instances, sometimes the problem will tell us that the substance, melted, froze, or evaporated.

Ariana Iranmahboub1G

Because since we would want to calculate k2, every other variable in the equation must be constant and not changing. Like how tempertature one and two will have to be a set value, delta H and delta S must also be a set value.

Ariana Iranmahboub1G

It could be both. This equation also helped us derive the other equations for entropy such as S=nCIn(T2/T1) , S=nRIn(V2/V1), and S=nRIn(P1/P2). So sometimes you won't have to solve for qrev directly if you can use those equations.

Ariana Iranmahboub1G

If it is a irreversible reaction, you would want to use w = -P*deltaV or w=deltan*R*T. If it is a reversible reaction, you would want to use w = -nRTIn(V2/V1).

Ariana Iranmahboub1G

If you are using the reverse reaction, you would flip the sign of delta H.

Ariana Iranmahboub1G

Can someone show me step by step on how to solve for number 10. I did not understand why q(ice)=q(water).

CHEM MOD: q(ice) = -q(water) DO NOT forget the negative sign. The heat released from one material in a system is absorbed by the other material in the system.

Ariana Iranmahboub1G

heat capacity is an intensive property because the amount of substance matters.

Ariana Iranmahboub1G

When should we use Cv (molar heat capacity of a gas at constant volume) over Cp (molar heat capacity of a gas at constant pressure) when we solve for q=nC(deltaT) or q=mC(deltaT)?

Ariana Iranmahboub1G

Yes, there is a Hess type approach to calculating Gibbs Free Energy. You can calculate total delta G by adding or subtracting delta G(reaction 1) and delta G(reaction 2).

Ariana Iranmahboub1G

A calorimeter is often used to measure specific heat capacity, so reactions would have either have constant P(find change in enthalpy) or constant V(bomb calorimeter). The example reaction Dr. Lavelle used in class was a constant P calorimeter that mixed HCL with NaOH.

Ariana Iranmahboub1G

Delta H the amount of heat released or absorbed at a constant pressure and is a state property. Delta U is the change between final integral energy, U, and initial integral energy, in which U is also a state property. In a closed system, delta U is the energy transferred by heating (positive q) in a...

Ariana Iranmahboub1G

Pressure is always positive. So when there is expansion, positive delta V, energy is released, so the work done by the system must be negative. On the other hand, when there is compression, negative delta V, energy is absorbed, so the work done by the system must be positive.

Ariana Iranmahboub1G

Because it can reach equilibrium with the pressure of its surroundings, it will remain at constant pressure. And since the surroundings is so large, the pressure is unchanging.

Ariana Iranmahboub1G

Can someone explain to me the concept of degeneracy (W) and how to calculate it.

Ariana Iranmahboub1G

The term q is heat, which is energy transfer due to thermal reactions. On the other hand, enthalpy, delta H, is the total amount of heat released or absorbed at a constant pressure. Therefore, delta h is a state property, but q is not.

Ariana Iranmahboub1G

Yes since the C-H bond does not break in the reactants, but the additional C-H in the products means that one C-H bond was formed.

Ariana Iranmahboub1G

pKa and pKa are the -log of Ka/Kb. You can convert pH to Ka using 10^-ph. You can do the same with pOH by converting pOH to Kb using 10^-pOH.

Ariana Iranmahboub1G

Somewhat because essentially for the enthalpy method, it is reactants minus products because all the products have negative delta H since bond are formed and all the reactants have positive delta H since bonds are broken. And he standard enthalpy of formation method, the last method, subtracts the s...

Ariana Iranmahboub1G

I think it would depend on what information the problem gives you. However, I believe the standard enthalpy of formation is more accurate than using bond enthalpies.

Ariana Iranmahboub1G

Standard Reaction Enthalpy is when all the reactants and products are in their standard state at 1 atm. Standard Enthalpy of Formation is the formation of one mole of a substance from its elements in their most stable state form.

Ariana Iranmahboub1G

If the reaction proceeds forward, the products side will have a positive change and the reaction side will have the negative change. If the reaction proceeds the negative reaction, the reaction side will have the positive change and the product side will have the negative change. For instance, if th...

Ariana Iranmahboub1G

You would use ICE when the question gives you the initial concentration of the reactants and/or products, to later solve for the concentrations of the products or reactant when the the reaction is at equilibrium.

Ariana Iranmahboub1G

It's important to know that the stronger the acid, the weaker its conjugate base. Also, the stronger the base, the weaker its conjugate acid.

Ariana Iranmahboub1G

Yes, you calculate (equilibrium concentration)/(initial concentration) times 100 and if it is less than 5%, the approximation is valid.

Ariana Iranmahboub1G

It’s often used to convert partial pressure to the molarity or vice versa. It can also be used to understand the effect volume, moles, and temperature will be affected by a change in pressure. In terms of whether to use arm or bar, you units should be the same units you are using for your R constant.

Ariana Iranmahboub1G

If there is initially no products, then the change in concentration for products must be positive and the change in concentration for reactants must be negative. The same would apply for vice versa. Also if Q is less than K, then than the change in concentration for the products will also be positiv...

Ariana Iranmahboub1G

Since solids and liquids cannot affect the reaction at equilibrium they are not included in the equilibrium expression.

Ariana Iranmahboub1G

Yes, it means the concentration of the reactants and products at equilibrium.

Ariana Iranmahboub1G

In many cases, the question will ask to find Kc or Kp.The question may also give you partial pressures, so you would know you would need to find Kp and if it gives you concentration, you'll know you need to find the Kc. If you're in doubt, I think it should be fine if you simply write K.

Ariana Iranmahboub1G

If there is initially no products, then the change for the products must be positive. If the products side is positive, then the reactant side must have a negative change and the same is for vice versa.

Ariana Iranmahboub1G

In many questions, they ask whether or not to find Kc or Kp, so that would be a good indication of which one to use. I wouldn't use them interchangeably because if it is a partial pressure, you would want to use parenthesis when finding the equilibrium constant and if it is a concentration, you woul...

Ariana Iranmahboub1G

Ka is the acid dissociation constant and is used for weak acids and pka is the -log(Ka).

Ariana Iranmahboub1G

Heme is a ringlike organic compound that is known as porphyrin, which an iron atom is bonded too. There are four heme groups in hemoglobin. The iron atom is what binds oxygen as our blood travels through our vessels.

Ariana Iranmahboub1G

I think it is a good idea to know general atoms that make an oxide amphoteric such as Al and Be, but it’s not a bad idea to know the actual formulas too.

Ariana Iranmahboub1G

Strong acids and bases dissociate completely in aqueous solutions whereas weak bases and acids don’t.

Ariana Iranmahboub1G

For number 22 why can myoglobin bind to two O2 molecules?
In my notes from the lecture, Fe binds to only 1 02 since the heme complex and a protein results in Myoglobin, so how would myoglobin bind to two O2?

Ariana Iranmahboub1G

Oxoacids are acids that contain oxygen. They more readily lose H+ if the resulting anion delocalizes and stabilizes the negative charge.

Ariana Iranmahboub1G

pKa is used to measure how strong an acid is. It is measured by taking the negative log of Ka(the equilibrium constant). The smaller the pKa is, the stronger the acid.

Ariana Iranmahboub1G

There are two different definitions of acids and bases. The Lewis definition of an acid is that is a species that accepts an electron pair. The Bronsted definition of an acid is that an acid is a proton donor. The Lewis definition of a base is a species that donates an electron pair. The Bronsted de...

Ariana Iranmahboub1G

Hydrogen bonds are only present between hydrogen atoms and nitrogen, oxygen, or fluorine. For this reason, only lone pairs on N, O, or F can be able to form a hydrogen bond as no other atom can.

Ariana Iranmahboub1G

Yes, a polydentate ligand is a complex that has two or more donor atoms. Therefore, it must have more than one lone electron pair, so that it can have two or more bonding sites. If it has one binding site, then the ligand is monodentate.

Ariana Iranmahboub1G

A polydentate should have two or more lewis base sites so it can bond to two or more donor atoms.

Ariana Iranmahboub1G

Equilibrium arrows are used when the acid or base is weak because they are not completely dissociated, so the reaction will go back and forth. On the other hand, strong acids and bases would dissociate completely, so there would only be an arrow going in one direction.

Ariana Iranmahboub1G

I do not believe so because a sigma bond forms when two orbitals overlap end to end between the two atoms' nuclei which is the internuclear axis. On the other hand, pi bonds occur when the two orbitals overlap side by side, which is outside the sigma bond and the space between the nuclei (internucle...

Ariana Iranmahboub1G

I think it is very important to know that radicals are molecules with an unpaired electron and that they are highly reactive, can only exist for a short time, and can damage DNA because it can react with it.

Ariana Iranmahboub1G

As with molecules with one central atom, the central atoms that are the least electronegative are in the center. To determine the shape of the molecule, you would need to look at the molecular shape of each central atom independently.

Ariana Iranmahboub1G

A polar molecular has polar bonds with dipoles that do not cancel. Polar bonds form when the electrons in covalent bond are not equally shared. This occurs when the electronegativity difference is high which would increase the difference in charge and increases the ionic character of the covalent bo...

Ariana Iranmahboub1G

I believe radicals contribute the same to molecular shape as lone pairs do because both a lone pair and a radical would occupy an orbital.

Ariana Iranmahboub1G

We use brackets to show that anything inside the brackets is inside the coordination sphere.

Ariana Iranmahboub1G

As long as the problem has to do with material from the past week, it should be fine.

Ariana Iranmahboub1G

It is also good to know that polarizability (alpha) depends on the number of electrons and the size of the atom/molecule. So the greater the size and the number of electrons the molecule has, the greater polarizability it has. These electrons in the atom or molecule is what causes the electron disto...

Ariana Iranmahboub1G

Yes a hydrogen bond forms between hydrogen and N, O, and F. Dipole-dipole interactions form when two polar atoms/molecules interact. Ion-Dipole form when a ion interacts with a polar molecule. Ion-ion interactions form when two ions interact with each other. Dispersion (also called London Forces, in...

Ariana Iranmahboub1G

I do not believe the bond angles would differ because the single electron would still occupy an orbital; therefore, it would keep its molecular shape.

Ariana Iranmahboub1G

A hydrogen bond site is any bond between hydrogen and N, O, or F in a molecule.

Ariana Iranmahboub1G

Sigma bonds occur when two orbital overlap end to end. Pi bonds form when two orbitals overlap side by side. S and p orbitals can form sigma bonds; however, since there can be 3 p orbitals (Pz, Py, Pz) in a p subshell, only one can have a sigma bond. Therefore, only one of the p orbitals is oriented...

Ariana Iranmahboub1G

I think that amount would be the amount of energy required to break the integration because the attractive force is the strength of the bond. As for how they become "depolarized", these interactions are generally weak, so it is very likely. However, usually when they are broken they also q...

Ariana Iranmahboub1G

I don't know the exact formula but I believe it is good to know that polarizability (alpha) depends on the number of electrons and the size of the atom or molecule.

Ariana Iranmahboub1G

Because diethyl ether has no hydrogen bonded to the oxygen atom, which would be the electronegative atom, whereas butanol does have a hydrogen bonded to the oxygen.

Ariana Iranmahboub1G

I believe the f-block can also have an expanded octet rule because any element in the 3rd period or below can have an extended octet and all elements with an f block are below the 3rd period.

Ariana Iranmahboub1G

I understand how size and molar mass contributes to why the strength of interactions in H20 is greater than in H2S, but how does this explain why H20 has a higher melting point and boiling point than H2S?

Ariana Iranmahboub1G

This means that the strength of the bond is approximately -20kJ/mole for a hydrogen atom that is covalently bond to an electronegative atom to bond to another close electronegative atom that has an available lone pair. The reason why it is negative is because the force is attractive and all attracti...

Ariana Iranmahboub1G

This was an exception because all the orbitals in N's 2p subshell are half-filled. On the other hand, the orbitals of O's 2p subshell were not half-filled or fully-filled.A subshell with half-filled orbitals have more energy since it is more symmetric than orbitals that are not half-filled or fully-...

Ariana Iranmahboub1G

Fist you'll want to count the total number of valence electrons for N20. For N20, there will be 16 valence electrons (2*5 + 6). Then, I would draw a lewis structure that fulfills the octet rule. Then you calculate the formal charges. With simply single bonds, you'll find that the formal charge of th...

Ariana Iranmahboub1G

Yes, the larger the anion is, the larger distortion it causes and the higher its polarizing power is. As a result, the ionic bonds have more covalent character. Therefore, the increasing covalent character makes them less soluble.

Ariana Iranmahboub1G

I think the reason why the attractive forces are negative is because repulsive forces are positive and attractive forces are negative. This is because repulsive forces are from two charges that are alike, and a negative charge times a negative charge is positive. On the other hand, attractive forces...

Ariana Iranmahboub1G

It's asking which metal ion would have that ground state electron configuration. Since it's asking for an ion (M2+), the answer must be an ion. For instance, for (a), if the ground state electron configuration for M2+ is [Ar]3d 7, then the ground state electron configuration for the neutral element ...

Ariana Iranmahboub1G

Double and triple bonds are often used to make the Formal charges smaller since a formal charge = 0 is the most stable. It also depends on the number of valence electrons available to find the number of bonds an atom is likely to form.

Ariana Iranmahboub1G

I would make the carbon atoms to central atom because it has the lowest ionization energy compared to oxygen and hydrogen. So I would have the two carbons in the center and from there I would draw the bonds from the carbon atoms to the oxygen and hydrogen.

Ariana Iranmahboub1G

The spin projection quantum number (or spin magnetic quantum number), ms, only has two value (+1/2 for an arrow pointing up electron and -1/2 for an arrow pointing down electron) because an electron has two spin states. Since an electron can have either spin state, one electron from a paired electro...

Ariana Iranmahboub1G

Yes covalent bonds form when electrons are shared between two nonmetals.

Ariana Iranmahboub1G

I got the same answer. I converted 4.37 eV to joule and 1.5 x 10^3 km*s^-1 to m*s^-1. Then, I also used the formula, kinetic energy = energy of photon - work function, to solve for the energy of the photon. After, I used E = (h*c)/lambda to solve for the wavelength, which gave me the answer 1.52 X 1...

Ariana Iranmahboub1G

There's a paired electron when an orbital has two electrons. There's an unpaired electron when an orbital only has one electron. It may help to first write the electron configuration. a) Bi : [Xe] 4f14 5d10 6s2 6p3 The maximum number of electrons a p-subshell can have is 6 electrons, and thus three ...

Ariana Iranmahboub1G

I would first count the number of atoms for each element on both sides. Then, you would want to balance an elements once at a time. I would typically recommend to do Hydrogen and Oxygen last. Lastly, check to make sure each element has the same number of atoms in the reactants and in the products.

Ariana Iranmahboub1G

Electrons further from the nucleus would have more energy than inner electrons because they are more weakly held by the nucleus. Therefore, further electrons have greater potential energy than inner electrons. In order for the electron to move to a lower orbital it must release energy. However, for ...

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