CHEMISTRY COMMUNITY

EthanPham_1G

This might seem like a redundant question, but I would like some clarification of what resources we can use on the final? Thank you.

EthanPham_1G

I am confused about what the orders of reactions mean conceptually? I understand how to determine the order mathematically when given the rates and concentrations of reactants. I also understand how the graphs of the orders are derived from. But what does 0, 1st, 2nd order mean?

EthanPham_1G

Will we be given what the value for A is for the Arrhenius equation? I don't know how else you could solve for k without knowing it.

EthanPham_1G

Will we be given what the value for A is for the Arrhenius equation? I don't know how else you could solve for k without knowing it.

EthanPham_1G

What is the difference between a catalyst and an intermediate. Can a catalyst also be an intermediate and vice versa?

EthanPham_1G

005162520 wrote:Why does the slow step determine rate law ?

The slow step determines the overall rate law because the overall rate of the reaction can only be as fast as the slowest step. If that makes sense. It's kind of like how a chain is only as strong as its weakest link. Hope that helps? :)

EthanPham_1G

Sorry this post is unrelated to the topic, but I am concerned about what will happen for our final. Also, since classes were cancelled, how will we turn in the last homework assignment?

EthanPham_1G

If delta H is positive that means that heat is absorbed in the reaction. The heat is on the left with the reactants.

EthanPham_1G

Since the slow step determines the overall rate of the reaction, then typically if you are given the overall rate of the reaction that is the slow step.

EthanPham_1G

If the K value is smaller than 10^-4 then you can approximate the x value. You can double check this by using the 5% rule. If the percent ionization is 5% or less then it is ok to approximate the x value.

EthanPham_1G

If delta H is negative that means that there is a release of energy so the reaction is exothermic.

EthanPham_1G

So apparently, H20 is what is getting oxidized in the anode instead of SO4? Is this because SO4 is a spectator ion?

EthanPham_1G

The left side of the cell diagram should be the anode reaction (oxidation). The right side of the cell diagram should be the cathode reaction (reduction). They are separated by the salt bridge or double line. Don't put reactants on the left and products on the right. The cell diagram is depicting th...

EthanPham_1G

Electrons move from the anode to the cathode. The anode side is getting oxidized, so there is a loss of electrons. The cathode sign has a reduction reaction so there is a gain of electrons. The electrons flow throw the galvanic cell which generates a current of electrons and therefore a voltage.

EthanPham_1G

Since the appendix only gives all oxidation reactions in terms of reduction reactions, do we have to change the sign of the voltage?

EthanPham_1G

Since the appendix only gives all oxidation reactions in terms of reduction reactions, do we have to change the sign of the voltage?

EthanPham_1G

I solved for K for part b) In3+ + U3+ --> In2+ + U4+ and I didn't get the same answer as the solution guide? I used the Nernst equation and got around K=100 but the solutions in the back says 1x10^4. Can someone explain how to solve this problem?

EthanPham_1G

How are we supposed to find the cathode and anode reactions for the electrolysis of NiSO4? I found the cathode reaction for Ni+2 + 2e- --> Ni. I can't find the anode reaction in the appendix?

EthanPham_1G

What are the different separations in the cell diagrams? Why do you sometimes use commas, bars, and double bars?

EthanPham_1G

Why do we include Pt when there is no solid? What would the cell diagram look like if there was a solid that could act as the electrode?

EthanPham_1G

The anions and cations in the salt bridge dissolve in the solutions to maintain a charge balance so that the redox reaction can continue. The video on galvanic cells that Lavelle posted on his website actually really helped me understand this.

EthanPham_1G

In this problem we have to predict whether the reaction will shift toward products or reactants when the temperature is increased. " X_{2}\leftrightharpoons 2X where X is a halogen." How would we know how the reaction shifts without knowing the enthalpy of the reaction? What does X being a...

EthanPham_1G

How do I solve this problem?
Br2(l) -----> BrO3- +Br-

I don't understand how to balance the redox reaction when the Br is in both products.

EthanPham_1G

Heat and entropy are temperature dependent but because it is the CHANGE in heat and entropy it is not temperature dependent. The change remains the same.

EthanPham_1G

Oxidation is when a compound loses electrons in the reaction. Reduction is when a compound gains electrons . You can memorize this with the acronym LEO the lion says GER. LEO=loss of electrons is oxidation, GER=gain of electrons is reduction.

EthanPham_1G

What is the difference between the reducing and oxidizing agent? Which one is being reduced and which one is being oxidized? How can you identify them?

EthanPham_1G

How do we determine the oxidation numbers and how it changed?

EthanPham_1G

Why do we have to split the reaction into half reactions? What if there are many reactants and products that it needs more than two half-reactions?

EthanPham_1G

What is the difference between intensive and extensive properties?

EthanPham_1G

Lead is a more complex molecule so it has more electrons, neutrons, and protons in one mole. Since there are more particles in lead, there is more degeneracy and therefore more entropy.

EthanPham_1G

Yes. Isothermal is another way to say reversible.

EthanPham_1G

Kennedi2J wrote:How do you know when to use q=mCAT/nCAT vs. q=CAT?

q=mCAT is used when you have the specific heat capacity. q=nCAT is used when you know the molar heat capacity.

EthanPham_1G

I was working on the following homework problem 4A.9: A piece of metal of mass 18.0 g at 100.0 C is placed in a vessel of negligible heat capacity but containing 50.2 g of water at 22.0 C. Calculate the final temperature of the water. Assume that no energy is lost to the surroundings. I ran into tr...

EthanPham_1G

What is internal energy? How would you solve for it if you know delta H?

EthanPham_1G

Can someone explain the Boltzmann equation and what it is used to solve for? What is W (degeneracy)? How do you solve for W.

EthanPham_1G

Can someone explain how the work formula w=-PdeltaV is an integral? Would we need to know that for the midterm and would we have to do calculus?

EthanPham_1G

What is the difference between work of expansion and work of compression?

EthanPham_1G

Can someone explain what work is? I honestly don't know. Thank you.

EthanPham_1G

Why is using bond enthalpy the least accurate way of calculating the change in enthalpy?

EthanPham_1G

How do you calculate bond enthalpies? I did not quite understand it when Professor Lavelle explained in class. Do you have to draw the lewis structures first? Does it matter how many of each type of bond there are? For example, if there are 4 C-H bonds in CH4, does that affect your calculation?

EthanPham_1G

Why is the standard enthalpy of formation for an element in its most stable form equal to 0? Are all elements included in this?

EthanPham_1G

Why is the standard state for a gas 1ATM, while the standard state for a solution 1M?

EthanPham_1G

Why is enthalpy (H) a state property but heat (q) is not a state property?

EthanPham_1G

If the Ka or Kb is less than 10^-3 then you can approximate x and you don't have to use the quadratic equation.
If the percent ionization is less than 5% then your approximation is correct.

EthanPham_1G

K is the equilibrium constant and can only be solved for when the concentrations of reactants and products at equilibrium are known. Q is the reaction quotient and can be solved at any point in the reaction, regardless if it is in equilibrium. If Q<K then the reaction moves forward and favors the pr...

EthanPham_1G

When we make the ice box for acids and base problems, how do we know if we need to use Ka or Kb to solve for x?

EthanPham_1G

What topics are being covered in test 1? Just chemical equilibrium and acids and bases?

EthanPham_1G

Does increasing the pressure/decreasing the volume change equilibrium according to Le Chatelier's Principle?

EthanPham_1G

Solids and liquids are not included in the equilibrium reaction and therefore shouldn't be used in the ICE box.

EthanPham_1G

Will adding/removing solids and liquids change the equilibrium at all according to Le Chatelier's principle?

EthanPham_1G

I understand that at equilibrium the rates at which the reactions occur are equal, but is the equilibrium constant K the rate at which these reaction occur? In addition, how can you speed up the rate at which a reaction occurs? K does not measure the rate at which these reactions occur. K is just a...

EthanPham_1G

K is the equilibrium constant for a reaction, a known, experimentally determined value. Q is the reaction quotient which determines the ratio between products and reactants in a reaction. Q can be solved for when the reaction is not in equilibrium. K can only be solved when the reaction is in equili...

EthanPham_1G

Kc is the equilibrium constant using concentration and Kp is the equilibrium constant using pressure. If you solved for Kc and Kp for the same reaction would they be the same value?

EthanPham_1G

Can someone explain to me a section of the notes? It was when he asked "Q2: A biological acid, HA, has pKa = 4.22. What's the Ka value of the acid?" I don't understand the part after that says "Is the acid neutral or negatively charged at pH 6?" and the little section under it. ...

EthanPham_1G

I believe it has to do with formal charge. An oxygen with a double bond will have a formal charge of 0.
FC=6-(4+(4/2))
FC=6-(6)
FC=0
If the oxygen had a negative formal charge, it would be able to act as a ligand.

EthanPham_1G

what are some molecules that are amphoteric but not amphiprotic? do we need to know molecules that fall into one category but not the other? Amphiprotic molecules are all amphoteric, but not all amphoteric molecules are amphiprotic if that makes sense. Amphiprotic means that it can either donate or ...

EthanPham_1G

I don't think we need to know anything about equilibrium for the final because it is a Chem 14B topic. I am pretty sure but to be safe you should ask a TA or Lavelle.

EthanPham_1G

Are you talking about intermolecular forces, because you just have to remember them. In order from strongest to weakest, it goes: ion-ion hydrogen bonding ion-dipole dipole-dipole dipole-induced dipole induced dipole-induced dipole You can also tell if the intermolecular forces are stronger if the m...

EthanPham_1G

Yes you're correct. If it's a positive charge we do not add anything. For example if the TM was chromium and the coordination complex was neutral or positive, we would write it as chromium. If the complex has a negative charge we would write it as chromate.

EthanPham_1G

Typically transition metals are always cations, meaning that they have positive charges. The -ate suffix at the end of ferrate only means that the entire coordination complex has a negative charge. The iron ion itself has a positive charge.

EthanPham_1G

Yes. So you already determined that hexacyanidochromate is [(CN)6Cr]-3. We know that this complex is an anion because of the suffix -ate after chromate. The one Cr has a +3 charge and CN has a -1 charge and there are six of them so it has a -6 charge. If you add +3 and -6, you find that the entire [...

EthanPham_1G

Ka is an equilibrium constant for acids. It is equal to Ka=[A-][H+]/[AH] (concentration of the products divided by the concentration of the reactants). Lavelle mentioned that only weak acids would have an equilibrium constant. This is because if it were a strong acid, it would dissociate completely ...

EthanPham_1G

Strong acids more easily lose the H+ protons to water. For example, H-I is a strong acid because the bond length between I and H are long and therefore weak; the H+ proton is easily lost. Because of this, the H-I acid dissociates completely in water. Compare this with H-F which is a weak acid. The H...

EthanPham_1G

What is the difference between these two definitions? Is one more correct or more accepted as the definition for a base and acid?

EthanPham_1G

Can anyone provide an example of the naming with these prefixes? I would like to see how it's used.

EthanPham_1G

The metal ends in -ate if the whole coordination complex has a net negative charge. The example that Lavelle gave in class was [Ni(CN)4]-2.

EthanPham_1G

An atom's oxidation number is its charge. Since transition metals are normally cations, they would have a positive oxidation number.

EthanPham_1G

Did you mean anion? We know chlorine is an anion because it has 7 valence electrons and therefore has a -1 charge.

EthanPham_1G

Why do rod shaped molecules attract each other stronger than spherical molecules?

EthanPham_1G

Will we have to know the equation Lavelle gave us for interaction potential energy?

EthanPham_1G

An example of a lone pair-bonding pair repulsion would be sulfur tetrafluoride, SF4. It has 5 areas of electron density: 4 bonding pairs and 1 lone pair. The lone pair on the central sulfur atom repels the four bonding pairs and reduces the bond angle.

EthanPham_1G

The symmetry of a Lewis Structure can be an indicator of polarity. For example, CCl4 has a carbon atom surrounded by four chlorine atoms of equal electronegativity. Because it is a symmetrical molecule, the dipole moments of the four chlorines cancel and it is a nonpolar molecule. This would not be ...

EthanPham_1G

In lecture, Lavelle spoke about how you can tell if a molecule is polar or non-polar if it has polar or non-polar bonds. Polar bonds have an electronegativity difference between the two atoms and non-polar bonds do not have an electronegativity difference. If there are polar bonds, the molecule can ...

EthanPham_1G

What is polarizing power and what does it do? Which atoms have a higher polarizing power?

EthanPham_1G

Why are ionic compounds more soluble in water while covalent compounds are not?

EthanPham_1G

Why do hydrogen bonds only work in molecules with N,O,F atoms (i.e. atoms with high electronegativity) when the Chlorine atom is more electronegative than Nitrogen. Why does it not also work with Chlorine?

EthanPham_1G

In Professor Lavelle's lecture, why did he use boiling points to indicate which dipole attractions are stronger?

EthanPham_1G

What causes an induced-dipole induced-dipole to occur between two atoms?

EthanPham_1G

Do the noble gases experience the periodic trends of ionization energy and electron affinity? If they don't, why are they different from other elements?

EthanPham_1G

Electron affinity is the energy released when an electron is added to a neutral atom in the gas phase. Electron affinity has the same trend as ionization energy. It increases left to right across a period and up a group.

EthanPham_1G

How would you know the charge for a transition metal in the d-block?

EthanPham_1G

Why are anions larger than cations?

EthanPham_1G

Can someone explain why having a d-shell allows an atom to have an expanded octet?

EthanPham_1G

Can someone explain what the purpose of resonance structures are? Do we have to draw all the resonance structures for every molecule's Lewis structure?

EthanPham_1G

Why is the second ionization energy always much higher than the first ionization energy?

EthanPham_1G

Can someone explain what electron affinity is? Lavelle defined it as the energy released when an electron is added to a gas-phase atom. If the energy released is greater, does this mean that the electron affinity is greater?

EthanPham_1G

Do we have to write 4s after 3d in electron configurations? And why is the energy of the 3d orbital less than the 4s orbital only if it is partially filled?

EthanPham_1G

When writing electron configurations for the p-orbital, do we have to write px, py, pz?

EthanPham_1G

In lecture today, why did Prof. Lavelle say that Schrodinger's wave equation can be solved for 1 electron atoms? Can it not be used for other atoms?

EthanPham_1G

Why is it that ml can be -1, 0, or 1 when l is 1, but ml can only by 0 when l is 0?

EthanPham_1G

Does anyone know how the quantum numbers are derived? I know that l is n-1 and ml is l-1, but why is this?

EthanPham_1G

I understand that the Hamiltonian in Schrodinger's equation is a double derivative. But what is it taking the derivative of? Is it a wave function?

EthanPham_1G

Can someone explain what the electron spin is? And what determines how/in what direction the electron spins?

EthanPham_1G

The DeBroglie equation is used to find the wavelength of anything that has momentum (mass in motion). With the DeBroglie equation, we can tell if an object displays wave-like properties, depending on its mass.

EthanPham_1G

Can someone explain why all matter has wavelike properties, but only matter with a small mass can have noticeable wavelike properties?

EthanPham_1G

I think that increasing the intensity of light results in more photons being emitted. However, in the photoelectric experiment, the frequency is what determines whether an electron is ejected. This is because the frequency of the wave determines the energy of each individual photon.

EthanPham_1G

It is based on the parameters of the individual question. In the photoelectric experiment, the energy of a photon (E=hv) must be greater than or equal to the work function, the energy required to remove an electron from a metal surface. The work function will not be the same in every problem, so the...

EthanPham_1G

In lecture, why did Professor Lavelle tell us not to use the Rydberg equation and instead use E=-hR/n^2 ?

EthanPham_1G

Hi guys! In today's lecture, what did Professor Lavelle mean by the variable "n" and how does it affect the energy of an electron?

EthanPham_1G

Thanks for answering!
I have another question. What does the variable "n" mean and how does it relate to the energy of an electron?

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