CHEMISTRY COMMUNITY

Katie Kyan 2K

Changing the mass of the electrode will not affect the cell potential.

Katie Kyan 2K

This is because the standard gibbs free energy for Cl2 is 0 as diatomic molecules are already in their standard state. Thus when calculating the delta G of the reaction we exclude the delta G for Cl2 since it is 0.

Katie Kyan 2K

I think I would keep the units in Kelvin because this is usually what we work with and most likely the temperature will be given to you in Kelvin.

Katie Kyan 2K

I'm not sure what you mean by cell notation but in a cell diagram your anode is on the left hand side and the cathode is on the right hand side.

Katie Kyan 2K

You have to check the overall charge of the compound in order to find the oxidation number of the elements. For example for MnO4-, we know that the charge of oxygen is 2- so with four oxygens this makes up a charge of 8-. The overall charge of the compound is 1- so that means the charge of Mn must b...

Katie Kyan 2K

You can use either but if you are trying to find the pH as in some of the HW problems, it would be easier to use the log version so you can find -log{H3O+].

Katie Kyan 2K

This relationship comes from the equation Estandard=(RT/nF)lnK which is derived from the Nernst equation where E=0. If the value of K>1 then Estandard>0 which means the reaction is spontaneous according to the equation G=-nFE as G<0.

Katie Kyan 2K

You can find n when you are balancing your redox reaction. n is the moles of electrons being transferred in the balanced reaction.

Katie Kyan 2K

You use platinum when your half cell reactions don't have a solid metal conductor to transfer the electrons from anode to cathode.

Katie Kyan 2K

You can use either but keep in mind that 2.303logx=lnx which is why we see two forms of the Nernst equation for standard conditions. There is E=E°-(0.05916V/n)logQ as you mentioned and E=E°-(0.025693V/n)lnQ that uses the natural log instead.

Katie Kyan 2K

A 1.0 m NiSO4(aq) solution was electrolyzed by using inert electrodes. Write (a) the cathode reaction; (b) the anode reaction. (c) With no overpotential at the electrodes, what is the minimum potential that must be supplied to the cell for the onset of electrolysis? How do we determine which is the ...

Katie Kyan 2K

An electrode has to be a solid metal as the previous response notes above. If the reaction has a solid metal that can conduct electrons from anode to cathode then an inert electrode like Pt is not needed. However, if there is not metal present to conduct the electrons then you would add Pt.

Katie Kyan 2K

Take a look at the charge of the Mn in each. For MnO4- we know that the charge of Mn is 7+ whereas the charge of Mn2+ is simply 2+. If Mn is going from 7+ to 2+ where there is a decrease in its oxidation number, we know that electrons must be gained for this decrease to occur. Thus, a gain in electr...

Katie Kyan 2K

A galvanic cell involves a spontaneous redox reaction that produces electrical energy. Meanwhile an electrolytic cell is not spontaneous and requires an external electrical source to generate a potential difference for electron flow.

Katie Kyan 2K

You'll know when to use an inert electrode like platinum when the reaction doesn't have a metal that allows electrons to be conducted from anode to cathode.

Katie Kyan 2K

Either H+ or H3O+ would work in balancing acidic solutions. You would use OH- when trying to balance basic solutions however.

Katie Kyan 2K

Yes you would use 8.314 J/mol*K because the units for Gibbs Free Energy involves J/mol or kJ/mol. Thus, when using the equation delta G= -RTlnK you would use 8.314 J/mol*K as the value of the Gas constant.

Katie Kyan 2K

Yes in this case Cl2 would be both the oxidizing and reducing agent. One half reaction involves the reduction of Cl to Cl- and the other half reaction involves the oxidation of Cl2 to HClO.

Katie Kyan 2K

If the free energy of the products is greater than that of the reactants, the reaction is not spontaneous and would most likely not take place.

Katie Kyan 2K

The beginning of the question tells us that the reaction is exothermic. When temperature is increased in an exothermic reaction, the reaction will proceed to the left. Therefore when the reaction is heated (temperature increase), the reaction will shift to the reactants, decreasing the equilibrium c...

Katie Kyan 2K

According to Le Chatelier's Principle, the system will adjust to maintain equilibrium. As a result, if you remove some NO from the system, the system will shift to the left to produce more NO and maintain this equilibrium. If the system shifts to the left, more NO2 is being used to produce NO. Thus,...

Katie Kyan 2K

I believe we only need to know the values for monoatomic gases. These formulas should be given on the formula sheet as well.

Katie Kyan 2K

Using the Ideal Gas Law we know that PV=nRT where P and V have an inverse relationship. This is why we can use P1/P2 in place of V2/V1.

Katie Kyan 2K

Since it says that this takes place in a thermally insulated vessel, we know that the delta S for the surroundings is 0 since no heat is being transferred to the surroundings.

Katie Kyan 2K

You can use the equation for the volume of a cylinder which is pi(r^2)h. Since you know the diameter of the pump, you can find its radius and the delta h would be 20. cm because this is how far the pump is depressed.

Katie Kyan 2K

For any isothermal expansion or compression of an ideal gas, the delta U would be equal to zero because there is no change in temperature. As a result, q=-w for both irreversible and reversible isothermal expansions.

Katie Kyan 2K

There is also a delta in front of the entropy as it is a state function meaning that you can subtract its final and initial states.

Katie Kyan 2K

Yes I agree with the previous commenter that the negative sign should be given to the water since the water is releasing heat in order to melt the ice cube.

Katie Kyan 2K

You should familiarize yourself with the equations but also know that many of them are related like deltaU=q+w and deltaU=deltaH-P*deltaV.

Katie Kyan 2K

You can use Kp when the equilibrium reaction involves gases! You'll usually know when to use Kp if the units for the amount of gasses refers to the partial pressure.

Katie Kyan 2K

A constant-volume calorimeter was calibrated by carrying out a reaction known to release 3.50 kJ of heat in 0.200 L of solu- tion in the calorimeter (q 5 23.50 kJ), resulting in a temperature rise of 7.32 8C. In a subsequent experiment, 100.0 mL of 0.200 m HBr(aq) and 100.0 mL of 0.200 m KOH(aq) wer...

Katie Kyan 2K

A closed system can only be changed by a change to pressure or volume. In a closed system no energy or matter can leave the system.

Katie Kyan 2K

You calculated the change in temperature wrong. It should be final temperature - 100.

Katie Kyan 2K

No you would not take into account the sig figs of conversion factors like the example you gave. Use the sig figs from the numbers the problem gives you instead.

Katie Kyan 2K

Can anyone explain to me why steam causes severe burns? Is it because the phase change from liquid to vapor requires a lot of heat to be supplied resulting in a large enthalpy?

Katie Kyan 2K

A closed system is when energy from the system can be exchanged with the surroundings. Meanwhile an isolated system is when nothing in the system can be exchanged with the surroundings.

Katie Kyan 2K

You can calculate Kp using the equilibrium partial pressures or by using the Kc. To convert from Kc to Kp you would use the ideal gas law equation.

Katie Kyan 2K

Leila_4E wrote:It's fine to have a negative pH sometimes, right? I got it once on a homework problem and I was worried I was doing it wrong.

it's definitely possible to get a negative pH. That would mean the acid has a hydronium concentration greater than 1.

Katie Kyan 2K

I think knowing the typical weak acid/weak base equilibrium equations are useful. As long as you know that HA + H20 => A- + H3O+ and A- + H2O => HA + OH- then you should be able to write the equations for a weak acid weak base problem.

Katie Kyan 2K

You can solve for a hydroxide/hydronium concentration knowing that the hydroxide concentration times hydronium concentration is equal to 1.0x10^-14

Katie Kyan 2K

Reducing the reactant causes the reaction to shift to the left to make more of the reactant and restore equilibrium.

Katie Kyan 2K

Yes as long as the percent ionization is less than 5% of the initial concentration then the approximation is okay. If the equilibrium constant is less than 10^-3 then you do not have to use the quadratic equation and to check, you would calculate the percent ionization as confirmation.

Katie Kyan 2K

In this case you'd just put 0.22 bar into the ICE box because you would be using Kp NOT Kc. Thus there's no need to try to find the concentration of the gases as you are given the initial pressure of HCl.

Katie Kyan 2K

In this question you would put 0.22 bar into the ICE box for initial pressure of HCl. To find the equilibrium partial pressures you need to use the equilibrium constant for the decomposition of HCl which is given as 3.2x10^-34. After completing the ICE box you should get: 3.2x10^-34 = x^2/(0.22-2x)^...

Katie Kyan 2K

If the temperature increases, would the value of K increase too? When changing temperature the value of K will increase or decrease depending on whether the reaction is endothermic or exothermic. If the forward reaction is exothermic, increasing the temperature shifts the reaction to the left which...

Katie Kyan 2K

To calculate the reaction quotient you have to calculate the concentration of each species by converting mmol to moles and dividing by the volume 0.500 L. From there you can calculate Q in order to see if the reaction is at equilibrium meaning that Q should be equal to K. However, in this case, Q is...

Katie Kyan 2K

When writing the equilibrium constant expression we don't include solids and liquids because, as Dr. Lavelle said in class, the molar concentration of a pure substance doesn't change in a reaction and thus, does not need to be included.

Katie Kyan 2K

I think for an equation involving gases, either Kp or Kc can be used since you can convert from one to the other using the Ideal Gas Law.

Katie Kyan 2K

Changes in pressure do not affect K as Dr. Lavelle mentioned in class. Adding an inert gas to increase pressure does not affect the moles of the reactant or product and the volume remains constant. Similarly, changes in volume also do not affect K as the system will try to restore equilibrium throug...

Katie Kyan 2K

When N2 is increased the reaction will shift to the right and when NH3 is increased the reaction will shift to the left. When H2 is decreased, the reaction will also shift to the left. Going to the left or right just means that either the products (right) or reactants (left) are favored in order to ...

Katie Kyan 2K

No you would leave out the solids and liquids when calculating Q.

Katie Kyan 2K

In this case you can think of the reaction between the CaO and HCl as a limiting reaction. This is because there is not an equal amount of strong acid and strong base being mixed in the flask. As a result you have to calculate the moles of HCl and the moles of CaO. Then, find how many moles of acid ...

Katie Kyan 2K

Yes van der Waals forces and London dispersion forces are the same. They are present everywhere because there always exists temporary fluctuations in electron density.

Katie Kyan 2K

To find the oxidation state of the transition metal in a coordination compound you have to look at 1) the overall compound charge and 2) the charges of the ligands bonded to the metal. For example, in [Fe(CN)6]4- we see that the charge of the entire compound is 4- and we also know that the charge of...

Katie Kyan 2K

How do we know if a coordination compound has a tetrahedral or square planar structure?

Katie Kyan 2K

The number of atomic orbitals is equal to the number of hybrid orbitals. For example in CH4, the carbon atom has 4 regions of electron density or four atomic orbitals. Therefore, it's hybridization is sp3 with a total of 4 hybrid orbitals each sp3 hybridized.

Katie Kyan 2K

A pi bond is formed when two p-orbitals overlap side to side. When C double bonds with C as in ethylene, the C atom has sp2 hybridization, leaving one unhybridized p-orbital with 3 hybridized sp orbitals. These sp orbitals form sigma bonds with other atoms while the unhybridized p-orbital of one C ...

Katie Kyan 2K

A Lewis acid can be thought of as an electron pair acceptor whereas a Lewis base is an electron pair donor. Ag+ is a cation that wants to accept an electron pair and does not have several electron pairs to donate.

Katie Kyan 2K

Cisplatin is a chemotherapy drug that forms a coordination compound with DNA to stop cell division. In binding to DNA, cisplatin helps stop DNA replication.

Katie Kyan 2K

How do we identify if a ligand is polydentate?

Katie Kyan 2K

Anisha Chandra 4H wrote:If we do use the -ate, would be cobate or cobaltate?

If we use the -ate it would be cobaltate.

Katie Kyan 2K

We can say that the bond angle is slightly less than 109.5 degrees. However, I think we should still know that water has bond angles of 104.5 degrees since it is particular to that molecule.

Katie Kyan 2K

How can we tell if the bond angle should be equal to a certain degree or less than the certain degree. An example of this can be ClO2+... The shape is bent, but I don't know how to tell that it is less than 120 degrees instead of just exactly 120 degrees. Generally a bond is equal to a certain degr...

Katie Kyan 2K

I think you should know that in a single bond there is 1 sigma bond. For a double bond there is 1 sigma and 1 pi bond and in a triple bond there is 1 sigma and 2 pi bonds. Moreover, sigma bonds interact end to end whereas pi bonds overlap side by side.

Katie Kyan 2K

Induced dipole induced dipole and London Dispersion forces are the same thing. Induced dipole induced dipole occurs between two nonpolar molecules without permanent dipoles. Meanwhile, dipole induced dipole occurs between a polar molecule (with a permanent dipole) and a nonpolar molecule.

Katie Kyan 2K

Bent and angular are the same thing. We can use either one to name structures.

Katie Kyan 2K

Because in biology, the form of a molecule is vital for its function. The fact that pi bonds don't allow for rotation locks the molecule into a certain shape at double and triple bonds which allow molecules to do its function. Also, the fact that pi bonds don't allow for rotation leads to cis and t...

Katie Kyan 2K

Electron pair geometry refers to the arrangement of electron groups and takes into account the lone pairs in a molecule. However, molecular geometry takes into account the number of bonds AND the lone pairs. For example for NH3, the electron geometry is tetrahedral whereas the molecular geometry is ...

Katie Kyan 2K

We can tell that CHI3 has a higher melting point compared to CHF3 by looking at the size of Iodine versus Chlorine. Since Iodine is bigger than Chlorine with a bigger molar mass, it is more polarizable and has stronger attractive interactions. As a result, CHI3 has stronger London Dispersion Forces ...

Katie Kyan 2K

Test 2 is next week (Week 8) in your discussion section.

Katie Kyan 2K

The fact that it has 3 bonds and a lone pair makes the bond angles slightly less than 109.5 degrees. This is because the lone pair electrons are closer to the central atom than the bonding electrons and pushes the bonds closer. Moreover, the lone pair has a greater electron density making the bond a...

Katie Kyan 2K

Yes, the first step is to draw the Lewis Structure of NH2OH. From the Lewis Structure we see that there is hydrogen bonding from the bonding of the H atom (covalently bonded to the N atom) and the other N atom. Since all molecules have London forces, these are also present. Lastly, dipole dipole for...

Katie Kyan 2K

A structure that is trigonal bipyramidal has 5 bonding pairs of electrons around the central atom. However, a structure with 3 bonding pairs and 2 lone pairs is T-Shaped as the lone pairs change the bond angle and orientation of the molecule.

Katie Kyan 2K

I don't think the question is asking you to calculate the exact bond angle. Knowing that the shape of SOCl2 is trigonal pyramid and that there are 4 regions of electron density involving one lone pair and 3 bonding pairs, the O-S-Cl bond angles are identical. Since SOCl2 has one lone pair, this lone...

Katie Kyan 2K

The original purpose of the photoelectric experiment was to test which metals held onto electrons more tightly. However, due to the unexpected outcome that light had to be interpreted as packets of photons, it became known as the photoelectric effect.

Katie Kyan 2K

It depends on the charge of the molecule. If the charge is 0 (neutral) then we are looking for a Lewis Structure where preferably all the formal charges on the atoms are 0. This would be the most stable structure. However, if the molecule is charged, then we want to put the negative charge on the mo...

Katie Kyan 2K

If we look at the quantum number for the period 3 elements like P, S, and Cl we see that for n=3, l=0,1, or 2. Even though for the ground state electron configuration, the electrons of the period 3 elements do not fill the d orbital, they have the ability to as we can see from the angular quantum nu...

Katie Kyan 2K

The most stable Lewis structure would be the one with the negative charge on Oxygen because Oxygen is more electronegative than Nitrogen. We don't put charges on elements with lower Electron Affinity.

Katie Kyan 2K

When the problem gives you the uncertainty in the + or - form, you have to multiply that value by two because it gives you the range of uncertainty. In the Dino nuggets problem since the uncertainty was + or - 0.34 m/s, the range of values the velocity can take on is (373.23+0.34) - (373.23-0.34) = ...

Katie Kyan 2K

C-F has more ionic character than C-Br because the electronegativity difference between C and F is greater than that of C and Br. Also, since we know that Fluorine is the most electronegative element, the shared electrons will be more strongly pulled towards Fluorine inn C-F than towards Bromine inn...

Katie Kyan 2K

The strength of a bond is determined by how much energy is needed to break the bond (dissociation energy). Since single bonds are the weakest type of bond, it takes the least energy to break. Next is the double bond and the triple bond has the most energy because it is the strongest and requires the...

Katie Kyan 2K

You make the change in energy negative when you know that energy is going to be released/emitted. For example in problem 11 from today's review session, the change in energy is negative because the electron is jumping down from n=3 to n=1. When an electron goes to a lower energy level, energy is bei...

Katie Kyan 2K

You use the equations involving light when you are dealing with light and Electromagnetic waves. The main equation is speed of light = wavelength x frequency. However anytime you are dealing with something that has mass and is moving, we use de Broglie's equation where wavelength = Planck's constant...

Katie Kyan 2K

For an electron to be distorted this means that the electron is polarizable. When the electrons of an anion are attracted to the cation there is a distortion of the electron cloud that causes the electron density to be affected. The more electrons there are, the more the electrons are distorted, and...

Katie Kyan 2K

Elements that can have expanded octets are the elements in row 3 and beyond. If we look at the principal quantum number for period 3 elements (n=3), we see that the angular momentum number can be all values up to n-1. This means that the angular momentum number can take on the values of 0,1, or 2. S...

Katie Kyan 2K

Today in class Dr. Lavelle said that resonance spreads multiple bond character over a molecule and also lowers its energy. Can someone explain why energy is lowered for a bond when a molecule has resonance?

Katie Kyan 2K

The angular momentum number (l) helps specify an s, p, d, or f orbital. More specifically, it describes the subshell of the orbital. Listed below is the orbital that corresponds to the angular momentum number:
l=0, s-orbital
l=1, p-orbital
l=2, d-orbital
l=3, f-orbital

Katie Kyan 2K

Why does electron affinity increase as we go towards the noble gasses? The electron affinity is essentially measuring the attraction between an electron being added to a valence shell and the nucleus. Electron affinity increases from left to right across a period because the attraction of the elect...

Katie Kyan 2K

I agree that the threshold energy can be calculated through the equation (Energy of Photon) - (Energy needed to remove the electron) = Kinetic Energy of electron. If you are given the energy of the incoming photon and the excess energy or kinetic energy then you will be able to find the energy neede...

Katie Kyan 2K

Resonance structures are basically alternate Lewis structures for a molecule. We don't have to draw all the resonance structures each time we draw a molecule's Lewis structure (unless the question specifically asks you to do so). You just have to know that some structures have multiple bonds in diff...

Katie Kyan 2K

The wave particle duality makes you unable to determine the specific position of an electron because it tells us that an electron has both wavelike and particle like properties. In this case, if an electron has both such properties, there is an uncertainty as described in the Heisenberg's Indetermin...

Katie Kyan 2K

I'm a little confused on the topic of wave functions. Are they the same thing as orbitals and why is it that squaring the wave function represents the probability of finding an electron?

Katie Kyan 2K

Yes I agree that this problem would just have to come down to memorization. In my discussion my TA told us that knowing the visible spectrum ranges from around 350-700 nm we can see how the second event is reading because the wavelength calculated is 600 nm which falls in this spectrum. From there, ...

Katie Kyan 2K

For part c of this problem you would use the following equation where Energy of Photon - Energy Required to Remove the Electron = 0.5mv^2 and then the equation E=hc/lambda to calculate the wavelength of the radiation that caused the photoejection of the electron. However for part a, the question is ...

Katie Kyan 2K

For the Hydrogen atom there are specific groups of spectral lines that show how energy levels are quantized. The two that we have to know are the Balmer Series and the Lyman Series. The Balmer series involves light from the visible region where n=2. The Lyman series involves light from the UV region...

Katie Kyan 2K

Knowing that a line is observed in the UV spectrum of atomic hydrogen and that there is an emission of energy tells you that this is the Lyman Series where the initial energy level is n=1. Thus, you can use the equation speed of light = wavelength x frequency to find the frequency at 102.6 nm. Then ...

Katie Kyan 2K

Knowing that 32 W = 32 J/sec, this means that 64 J will be emitted in 2 seconds. Therefore, you can find the Energy per photo for violet light of wavelength 420 nm using the equation E=hc/wavelength. Then, divide 64 by the energy per photon to get the number of photons emitted in that time interval ...

Katie Kyan 2K

For this problem, you find the moles and grams of C, H, and N. From there, add up the masses of C, H, and N and subtract the sum from the total mass which is 0.376 grams. This will give you the mass of Oxygen which should be 0.060 grams. Convert the grams of Oxygen to moles of Oxygen. After this you...

Katie Kyan 2K

Yes for balancing chemical equations you can only change the stoichiometric coefficients. Changing the subscript changes the molecule/compounds within the chemical equation making them different.

Katie Kyan 2K

For G23 you find the number of moles of NaCl and KCl, add the moles together and divide by 0.100 L to get the Molarity. This is because there is a 1:1 ratio of moles of NaCl to moles of Cl- and a 1:1 ratio of moles of KCl to moles of Cl-. The molarity of Cl- should be 0.13 M.

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