CHEMISTRY COMMUNITY

Soumya Ravichandran 4H

You can determine the spontaneity of a reaction by calculating delta G using standard reaction gibbs free energy values or by comparing the signs for enthalpy and entropy at fixed temperature values.

Soumya Ravichandran 4H

No, I don't think we would explicitly need to know what the intermediates are. However, like the example done in class, if a compound is in the chemical equation but not in the experimentally derived rate law, it is evident that it is an intermediate in the reaction.

Soumya Ravichandran 4H

A catalyst/enzyme does change the rate of the reaction by changing the activation energy needed for the reaction to proceed to completion.

Soumya Ravichandran 4H

The cold/heat pack is considered to be spontaneous because the question said that heat is being released. Since the reaction is exothermic, it is thermodynamically favorable, thus making the reaction spontaneous.

Soumya Ravichandran 4H

I didn't really understand the solution manual's answer for this question, if anyone can explain the answer in clearer terms that would be great!
Question: Some entries for Sm in Appendix 2A are negative. What is common about these entries, and why would the entropy be negative?

Soumya Ravichandran 4H

E does not change because if you look at the equation it is evident that delta G doubles when the stoichometric coefficients are doubled. However, the change in the number of moles, or delta n, also doubles. Since both delta G and delta n doubles, it does not affect delta E in the equation, meaning ...

Soumya Ravichandran 4H

You can tell which one is the oxidation and reduction reaction based on the oxidation numbers on the product side of the equation.

Soumya Ravichandran 4H

Can someone clarify the procedure for balancing O and H for redox reactions in basic solutions?

Soumya Ravichandran 4H

I think you can assume that oxygen will always be a charge of -2 and hydrogen will always be a charge of -1. Using the charge for this "given" elements, you can find the charge of the other elements, like manganese in this case.

Soumya Ravichandran 4H

What does free expansion mean? Does it just mean that there was a change in volume, and hence work was present in the system?

Soumya Ravichandran 4H

3/2 R is used for Cv of an ideal monoatomic atom. 5/2R is for Cv of a linear molecule and for Cp of an ideal monoatomic atom.

Soumya Ravichandran 4H

With regards to the different types of motion, rotation, translational, and vibrational, what changes between Cp and Cv causing the use of two different formulas (3/2R and 5/2R)?

Soumya Ravichandran 4H

Why can you only calculate delta S, when the q for the reaction is reversible?

Soumya Ravichandran 4H

Yes, this can occur when there is no volume change (free expansion), but generally speaking, delta H will only equal delta U when there is no work done and pressure is held constant

Soumya Ravichandran 4H

In lecture yesterday, what did Dr. Lavelle say the limitations are for using a bomb calorimeter as an isolated system?

Soumya Ravichandran 4H

When is heat capacity calculated? Is it for the slopes or the stagnant portions of the phase diagram?

Soumya Ravichandran 4H

Are both bond enthalpies and standard enthalpies of formation given by mol, meaning that we always have to multiply by the stoichometric coefficients? Also, for which method is do we say that the enthalpy of a pure substance is zero?

Soumya Ravichandran 4H

Why is enthalpy defined to be a state function?

Soumya Ravichandran 4H

Yes, this is because energy is released when bonds are broken, which is what occurs in the reactants. On the other hand, energy is needed to put the bonds back together, which is what occurs in the products.

Soumya Ravichandran 4H

Yes, you only account for the bonds broken and re-formed. However, Dr. Lavelle mentioned in class that you can also just break down all the bonds in the reacts and re-form all the bonds in the products to get the same answer though it might be a longer process for the calculations.

Soumya Ravichandran 4H

The modules give you a score on the post-assessment and tell you which questions you got wrong, but they do not show the correct answer.

Soumya Ravichandran 4H

Pressure, even when volume is changed, will not change your equilibrium constant, K. Temperature is the only physical parameter that can change K, concentration and pressure can shift the direction to which the equilibrium will go towards, but they will not change K.

Soumya Ravichandran 4H

If you are given Kp then it is evident that all your gases will be represented in an partial pressures. If you are given Kc, then report them as concentrations. You can easily convert between partial pressures and concentrations using the derivativion made from PV=nRT that we were shown in class.

Soumya Ravichandran 4H

For any concept associated with Le Chatelier's principle, such as pressure, temperature, or concentration, you do not include any solids or liquids.

Soumya Ravichandran 4H

When given gas phase reactants and products, is it best to put the concentrations in terms of atm and make the equilibrium constant Kp or put it in molarity and make the equilibrium constant Kc?

Soumya Ravichandran 4H

Other than pumping in an inert gas into a system, are there any other ways that the pressure of a system will not shift toward the reactants or products?

Soumya Ravichandran 4H

I think Dr. Lavelle said that we are covering this topic later on in thermodynamics. The outline for the textbook reading given on his website also omits these pages!

Soumya Ravichandran 4H

Basically, you can use an ICE table when you do not have the change in concentration given between the initial and equilibrium concentrations. By finding the change in concentrations, we can figure out the equilibrium concentrations, from only the initial concentrations and the equilibrium constant.

Soumya Ravichandran 4H

We know that when Q<K products are favored and reactants are favored when Q>K. What happens when Q=K?

Soumya Ravichandran 4H

For the ICE table that Dr. Lavelle mentioned in class today, why/do we always assume that products start at 0 if no numbers are given at the beginning for the initial condition?

Soumya Ravichandran 4H

I wasn't sure how to answer this question, since the concentration of H2O is only given before the reaction has reached equilibrium. A mixture of 2.5 moles H2O and 100 g of C are placed in a 50 L container and allowed to come to equilibrium subject to the following reaction: C(s) + H2O (g) ⇌ CO (g) ...

Soumya Ravichandran 4H

What is another way to distinguish between strong and weak acids and bases other than comparing dissociation constants (Ka and Kb)?

Soumya Ravichandran 4H

What are other ways of stabilizing an acid other than delocalizing the electrons? Also, does the concept of delocalizing the electrons only apply for oxoacids or for all compounds?

Soumya Ravichandran 4H

Are all the metalloids considered to be amphoteric oxides or are they just a subset? Are there any other examples that we should know that are not in the diagonal band mentioned in class?

Soumya Ravichandran 4H

High electronegativity means high delocalization power because the more an element wants to gain an electron, the more likely it is to want to delocalize a pair of electrons from another element.

Soumya Ravichandran 4H

The difference is in the way that they defined acids and bases. The Bronsted Acid is a proton donor, and the Bronsted base definition is a proton acceptor. According to the Lewis definition, and acid is an electron pair acceptor, and a base is an electron pair donor.

Soumya Ravichandran 4H

I think that he is planning on covering that on Wednesday when he talks more about chemical equilibria.

Soumya Ravichandran 4H

The difference between Arrhenius and Bronsted Lowry definition is that in the Arrhenius definition an acid is characterized by anything that has a H+ ion and a base as anything that has a OH- ion. The Bronsted Lowry definition is that acid is anything that is a proton donor, and a base is a proton a...

Soumya Ravichandran 4H

When do the bond angles of a molecular slightly differ from the expected one (ex. for some structures that are tetrahedral the bond angle is less than 109.5)?

Soumya Ravichandran 4H

What is the difference between molecular shape and electron pair geometry?

Soumya Ravichandran 4H

By knowing how many sigma and pi bonds there are in a molecule, we can know the strength of the interactions, since sigma bonds are generally stronger than pi bonds. Also, they are the result of overlapping orbitals in hybridization so they can predict the behavior of molecules.

Soumya Ravichandran 4H

Why does differences in the strength of polarizability give rise to different states of matter, (ex. pentane is a mobile fluid while octadecane is a waxy solid)?

Soumya Ravichandran 4H

What is interaction potential energies and why is it dependent on (r), the distance between two atoms or molecules?

Soumya Ravichandran 4H

Sometimes, octet formation is impossible as in the case of compounds such as SF6 where the octet rule is exceeded. The octet rule here is numerically impossible to satisfy but the idea is to keep the formal charges to zero. The only elements that are totally bounded by the octet rule are those in pe...

Soumya Ravichandran 4H

Obviously there are exceptions, but I think that it is better to have no formal charge on the central atom in order to have the Lewis Structure of the lowest energy and most stability. Also, if you add up the formal charges of all the elements it should equal the charge of the compound.

Soumya Ravichandran 4H

Why is dissociation energy always positive in a reaction?

Soumya Ravichandran 4H

With regards to why the energy is negative, I think it is because it takes a huge amount of energy to break the hydrogen bonds due to the difference in electronegativities. Since Fluorine is the most electronegative atom, the closer you bond hydrogen with an element next to fluorine, the higher the ...

Soumya Ravichandran 4H

In class, we said that Van der Waals forces and London Dispersion forces are synonymous when talking about nonpolar bonds. However, in high school chem I remember that Van der Waals encompassed a broader category which included even those with weak dipoles, so I was just wondering whether these term...

Soumya Ravichandran 4H

Can the differences in electronegativity be used to figure out any information about the structure of the molecule or is it solely used to determined the type of bond?

Soumya Ravichandran 4H

Does the concept of resonance structures only apply to shifting the strength (double/triple) bonds around the atom, or can it also apply to the shifting of the lone pairs?

Soumya Ravichandran 4H

Yes, it does. We covered in class these two elements as exceptions but also when we did electron configurations of ions, such as Cu+ we only removed the 4s1 electron, which proves that valence electrons are being affected.

Soumya Ravichandran 4H

In addition to looking at the Lewis Structure for the dipole moments, I think the difference in electronegativity can be calculated to differentiate between polar and nonpolar molecules. For example, polar molecules tend to have higher differences in electronegativities than nonpolar ones.

Soumya Ravichandran 4H

What other unit conversions are important to know for Test 2 other than that of nm to m?

Soumya Ravichandran 4H

No, I don't think the specific wavelengths are necessary. Rather, maybe just knowing the spectrum in order of increasing wavelength/frequency might be helpful since you can check if your answers are reasonable. Also, knowing that visible light is between 400-900 nm is important.

Soumya Ravichandran 4H

I wasn't sure of the answer for this question on the module assessment, if anyone knows!
When the energy per photon is equal to the energy required to remove an electron what is this energy called?

Soumya Ravichandran 4H

In class, Professor Lavelle mentioned to not use the Rydberg Equation when doing problems that had a change in energy state (ex. n=4 to n=2). When will this equation be used, and in what capacity if so?

Soumya Ravichandran 4H

When is the DeBroglie equation used in a problem, and will a problem specify if we need to use it? I'm wondering because the example in class mentioned "find the DeBroglie wavelength..."?

Soumya Ravichandran 4H

What is the difference between the term "energy released by a photon" and the "E" in the equation E=hv?

Soumya Ravichandran 4H

I think its best to keep the molar mass from the periodic table, and round it when doing calculations according to the number given in the problem. False accuracy should not occur because the molar mass values are standardized for all the problems.

Soumya Ravichandran 4H

I think the formulas for the hydrocarbons will be provided, but we need to know that when a question says combustion/oxidation/burning it will have a hydrocarbon + O2 --> CO2 + H2O.

Soumya Ravichandran 4H

For addition, the rule is to go with the number that has the least digits after the decimal point, so 12345.6 + 1.008 would have an answer that has only one digit after the decimal point, so the answer will be 12346.6. The rule about having the least amount of sig figs in the answer is for multiplic...

Soumya Ravichandran 4H

Sodium bromide, NaBr, which is used to produce AgBr for use in photographic lm, can itself be prepared as follows. Fe + Br2 --> FeBr2 FeBr2 + Br2 --> Fe3Br8 Fe3Br8 + Na2CO3 --> NaBr + CO2 + Fe3O4 What mass of iron, in kilograms, is needed to produce 2.50 t of NaBr? I understand the stoichometry for ...

Search found 62 matches