CHEMISTRY COMMUNITY

Andy Nguyen 1A

How do we know if there is a catalyst in a reaction mechanism?

Andy Nguyen 1A

I believe you should get a positive voltage since the cell is electolytic.

Andy Nguyen 1A

This is what I did: Cathode: 2H+ + 2e- --> H2 Anode: H2 --> 2H+ + 2e- Overall: 2H+ + 2e- + H2 --> 2H+ + 2e- + H2 If you cancel the H2 out you get: 2H+ + 2e- --> 2H+ + 2e- So I guess you are supposed to factor out the 2 to get only 1 electron being transferred. I think H2 cancels out because they are...

Andy Nguyen 1A

The +1.23 volts is for the oxidation reaction. The standard reduction potential is actually -1.23 V so the solution manual is correct. And you want to get the most negative value of E because in an electrolytic cell, the reaction is non spontaneous.

Andy Nguyen 1A

I think its because when you have the same species with different concentrations, the higher concentration of the species indicates that its the reactant while the lower concentration is the products. It's because the higher concentration will shift to the lower concentration to reach equilibrium, m...

Andy Nguyen 1A

Heisenberg is driving when he gets pulled over. When the police officer asks how fast he was driving, Heisenberg replies "No, but I know exactly where I am!".

Andy Nguyen 1A

I think we did something like this in class today, but I found this link which had the same question. Hope this helps! viewtopic.php?t=2561

Andy Nguyen 1A

The unit for k in a 0 order reaction is mol/(L*s). In a first order reaction, k is in 1/s. In a second order reaction, k is L/(mol*s).

Andy Nguyen 1A

What did the police molecule say to the suspect molecule? I got my ion you.

Andy Nguyen 1A

It's considered a pseudo rate law because the if the normal rate law is Rate=k*A*B*C, we have to change the concentrations of B and C to see how A affects the rate. So under the assumption that B and C are in excess and are constants, we use the psuedo rate law Rate=kprime*A, where kprime=k*B*C. I t...

Andy Nguyen 1A

Since the CO wasn't present we were able to assume it was a 0 order because it wasn't in the rate law. I think Dr. Lavelle mentioned that not all reactants actually affect the rate so in those cases they should have a 0 order as well.

Andy Nguyen 1A

These species that are added to the ends of the cell diagrams, like Pt, are inert electrodes that simply act as a way to transport the electrons.

Andy Nguyen 1A

I think it is because HCl is a strong acid, so it dissociates completely into H+ and Cl- ions.

Andy Nguyen 1A

I think Q is still calculated the same, but instead of using concentrations you are using pressures.

Andy Nguyen 1A

When we write out a skeletal equation, do we only include the species being reduced or oxidized?

Andy Nguyen 1A

I think that what you did is right since the ice melts so it becomes liquid water, so you have to use the specific heat capacity of water at a liquid. Was the enthalpy of vaporization in kJ/mol because that could effect how you convert the units. Hope this helps!

Andy Nguyen 1A

Using U=(3/2)*R*T, we know that this is the internal energy for an ideal gas. So that means the only thing changing U is temperature since (3/2) and R are constants. So since isothermal means the temperature doesn't change, deltaU=0.

Andy Nguyen 1A

I think that would be one of the only instances to use it. Dr. Lavelle has also used it to show that deltaU is 0 during isothermic processes, but I don't think we will use the equation too much.

Andy Nguyen 1A

What makes the cell potential an intrinsic property since we don't multiply it by anything when we do problems with half reactions?

Andy Nguyen 1A

I used those same numbers and got the answer from the book. I plugged in
-3920 kJ = deltaU + (-3 mol) * (.008314 kJ/Kmol) * 298K. Then I solved for deltaU.

Andy Nguyen 1A

Standard conditions are usually noted with a ° like in S° or H°.

Andy Nguyen 1A

Since the system is isothermal, we know that the change in internal energy is 0. So q+w=0, and q=-w. Since the balloon is expanding its volume against a changing pressure, work is being done. This also means that the energy lost during work is gained as heat, because the internal energy must stay 0....

Andy Nguyen 1A

When deriving equations, the book changes terms from delta S to dS or dq because they say the change is infinitesimal. What does this mean?

Andy Nguyen 1A

Normally, combustion reactions result in an increase in entropy. Based on the phase changes, we see that a solid changed into a gas and liquid, which means an increase in entropy.

Andy Nguyen 1A

I think it was just used to show that a reversible reaction does more work than an irreversible reaction.

Andy Nguyen 1A

What do you do with a dead chemist? You barium.

Andy Nguyen 1A

Since entropy is the number of states a system can have, is there units for entropy?

Andy Nguyen 1A

You use 298 K because you assume the system is at standard conditions, so the temperature is 25 degrees Celsius.

Andy Nguyen 1A

Cv(vap) is a constant, 2.01 (J/C*g). It was in table 8.2.

Andy Nguyen 1A

I think that delta U is only 0 for isothermal expansion on ideal gases.

Andy Nguyen 1A

Water expands when it freezes. How much work does 100 g of water do when it freezes at 0.0 degrees Celsius and pushes back the metal wall of a pipe that exerts an opposing pressure of 1070 atm? The densities of water and ice at 0 degrees Celsius are 1 g/cm3 and 0.92 g/cm3 respectively. I am having t...

Andy Nguyen 1A

Since it is an adiabatic process, no heat is transferred, so q must be 0 always. q would be negative if heat was allowed to transfer from the system to the surroundings, making the reaction exothermic.

Andy Nguyen 1A

I think we do need to know which bonds are formed and are broken because it will affect the value of the enthalpy of the reaction. The lewis structures are helpful to see which bonds are broken and formed.

Andy Nguyen 1A

I think in Hess's Law problems, the stoichiometric coefficients are often fractions to make the math easier. Multiplying by fractions just means you multiply the enthalpy by the same fraction as well.

Andy Nguyen 1A

To add on, if a reaction was exothermic, the enthalpy sign would be negative. So the reverse reaction would be endothermic, making the enthalpy sign positive.

Andy Nguyen 1A

What is the difference between the standard enthalpy of formation and the standard enthalpy of the reaction?

Andy Nguyen 1A

I think if you are given Q with Kc, then you can see how the reaction will shift. If Q<K, the reaction shifts right. If Q>K, the reaction shifts left.

Andy Nguyen 1A

I think to find the type of dentate a compound is you look at how many atoms have lone pairs. It helps to see the Lewis Structure and find those sites. For example, water has one atom, oxygen, with two lone pairs. Water is a monodentate because it only has one atom with a binding site.

Andy Nguyen 1A

A molecule is a polydentate if it has more than one atom that can bind to a central metal atom/ion at different sites. For example, ethylenediamine is a bidentate because if you look at the lewis structure, there are lone pairs on 2 different nitrogen atoms. In water, there are two lone pairs on the...

Andy Nguyen 1A

A neutron walks into a bar and orders a drink. When the neutron asks how much the drink was, the bartender replies "For you, no charge".

Andy Nguyen 1A

In lecture today we found the equation for kw, which was Kw= [H30+]*[OH-], from the chemical reaction 2H20 --> H30+ + OH-. Is H2O not part of the equation for Kw because it is in a liquid state? Dr. Lavelle also mentioned that it was because there was a large amount of water but I'm not sure what he...

Andy Nguyen 1A

What fish is made of two atoms? 2Na

Andy Nguyen 1A

When we calculate the equilibrium constant I know that we ignore solids and liquids. Do we also do this when using the ICE method? Thank you!

Andy Nguyen 1A

Did you hear oxygen went on a date with potassium? It went OK.

Andy Nguyen 1A

If the pressure isn't given in atm, then you can use 760 mmHg = 1 atm and 101.325 kPa = 1 atm.

Andy Nguyen 1A

The coordination number is just the number of bonds attached to the central metal atom.

Andy Nguyen 1A

If the Silver Surfer and Iron Man team up, they’d be alloys.

Andy Nguyen 1A

I don't trust atoms... they make up everything.

Andy Nguyen 1A

My reasoning for putting SiO2 as polar was because of the slight difference in electronegativity. Since there was a slight difference in electronegativity, the compound did have ionic properties, but was not completely ionic.

Andy Nguyen 1A

When you are drawing a Lewis structure, I think you have to look at the formal charges. NO3- has a double bond to minimize the formal charges of each atom because if there were lone pairs, the formal charge would not match the charge of the nitrate ion. Without the double bond, the formal charge of ...

Andy Nguyen 1A

From what I've looked at online, its another exception, so only Chromium and Molybdenum have different electron configurations.

Andy Nguyen 1A

Hi, just to add on, molecules that have a trigonal bipyramidal shape have more regions of electron density so these bonds are as far away as possible. A trigonal planar is only on one plane while the trigonal bipyramidal adds a 3rd dimension.

Andy Nguyen 1A

Hello, I am still confused on when light acts as a wave or a particle. In the photoelectric effect, light acted as photons to remove electrons, but in other experiments, light can act as a wave. Can someone clarify this? Thank you!

Andy Nguyen 1A

So was the fact that light can act as a particle the unexpected effect or was it something else?

Andy Nguyen 1A

I don't think there will be questions specifically on 1B and 1C, but the concepts might be used in problems on the tests. My TA told us that knowing the unit conversions can save time when doing stoichiometry. For 1C, it might be helpful to know the rules for significant figures when writing your an...

Andy Nguyen 1A

The textbook says that a mole of something has the same number of atoms in carbon-12, which is 6.02x10^23 atoms.

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