CHEMISTRY COMMUNITY

Hailey Boehm 2H

Why is change in internal energy zero for isothermal processes? is this always true?

Hailey Boehm 2H

What does pseudo first order mean? When would we have to apply this concept?

Hailey Boehm 2H

Why is ice melting a spontaneous process? Also, why is the combustion of gas spontaneous?

Hailey Boehm 2H

This question states, "Calculate the molar concentration of OH- in solutions with the following molar concentration of H3O+: ... (c) 3.1 mol.L-1" The solutions manual says that the solution is [OH-]=[1e-14]/[3.1e-3 M H3O+]
Why do you multiply 3.1 mol.L-1 by e-3?

Hailey Boehm 2H

On test #2 there is a question about the change in Gibbs free energy that would result from the melting of snow on a sunny day. I was able to determine that this process is endothermic, so deltaH is +, and this is a phase change from solid to liquid, so the change in entropy would be +. How can I us...

Hailey Boehm 2H

How do you figure out the largest E°cell on test #2? I though that you would have to pick the greatest reducer and weakest oxidizer to get the largest E°cell but I got the question wrong. thanks!

Hailey Boehm 2H

On the Van't Hoff Equation on Test #2, how do we plug the values into the equation (I assume the numbers each section had are different, so just a general explanation would work)? Is Kw-10-14 considered k1? and once we obtain a values for k2, how can we determine if the solution is acidic or basic? ...

Hailey Boehm 2H

How can you tell if thermodynamics or kinetics is controlling a reaction? Do we need to look at delta G differences of reactants and products?

Hailey Boehm 2H

When is an example of a circumstance where we would need to use the average rate? or what is an instance in which we would need to apply the average rate to a situation?

Hailey Boehm 2H

What is the difference between average rate, unique rate, and instantaneous rate (on a conceptual level)?

Hailey Boehm 2H

What exactly is n? and how do we determine it?

Hailey Boehm 2H

How does a pH meter work? Dr. Lavelle went over in class but I did not understand how it works.

Hailey Boehm 2H

Do we put H+ or H2O in cell diagrams?

Hailey Boehm 2H

What is the difference between Sm° and ∆Sf°? When would we generally need to use each respective value?

Hailey Boehm 2H

How do you know if a reaction is spontaneous based on its ΔG, ΔH, and ΔS values?

Hailey Boehm 2H

How does the salt bridge work in a battery? what way do the ions flow?

Hailey Boehm 2H

I think that the problem would have to specify if the solution was basic or acidic. When the solution is basic, for each H+, you have to add one OH- to both sides of the equation. Then you can later subtract H2O from both sides if possible.

Hailey Boehm 2H

What is the significance of utot= (3/2)NRT for an ideal gas and reversible expansion? When would I know to us this/ when does it apply?

Hailey Boehm 2H

What exactly is positional/residual energy? and is this what the value you get from boltzmann's equation is?

Hailey Boehm 2H

What exactly is the difference between Standard Reaction Enthalpy and standard enthalpy of formation? When do I use one versus the other??

Hailey Boehm 2H

I understand that 3/2*R is used in entropy calculations for ideal monatomic gases, but I am unsure exactly as to when I should use it versus just R. When exactly do I use it?

Hailey Boehm 2H

4C.3 in the 7th edition states, Calculate the final temperature and the change in internal energy when 765.J of energy is transferred as heat to 0.820 mol Kr(g) at 298K and 1.00 atm at (a) constant volume (b) constant pressure. Treat the gas as ideal. I don't understand how to approach this problem....

Hailey Boehm 2H

Is there an easy way to figure out what gas constant I should use? Which one is used the most often in the reversible expansion work equation, w= -nRTln(v2/v1)?

Hailey Boehm 2H

What is L.atm's relevance and why is this what you get when you do work calculations in SI units? Must we always multiply our answers by 101.325 J/ 1 L.atm when we are doing work calculations (like for ex. 4B.5 7th ed.)?

Hailey Boehm 2H

ΔU=Q+W
Can someone please explain to me the significance of this equation? and in what cases would q be 0?

Hailey Boehm 2H

How do you calculate q in a case of constant volume? I know that in a case of constant pressure you use qp= n*Cp*deltaT. Does it differ for Cv? I am confused about the relevance of Cp and Cv during calculating. Anything helps, thank you!

Hailey Boehm 2H

What exactly is standard enthalpy of formation? and why is it 0 when in the case of an element in it most stable form?

Hailey Boehm 2H

Why is there no change in the equilibria for the reaction 2 HD (g) = H2 (g) + D2 (g)? What are the rules for determining whether products or reactants will be favored in an instance where the pressure is increased?

Hailey Boehm 2H

This question states " (a) When the pH of a .01 M HClO2 (aq) was measured, it was found to be 1.2. What are the values of Ka and pKa of chlorous acid?..."
How do I start this problem? an ice chart?

Hailey Boehm 2H

How do you write out the chemical equation for AlCl3(aq) + H2O?

Hailey Boehm 2H

6D.17 in the 7th ed. states "Calculate the pH of: (a) .063 M NaCH3CO2 (aq) (b) .65 M KCN (aq)"
I keep getting the wrong answer, could someone walk me through how to do this type of question?

Hailey Boehm 2H

Question #14 on the chemical equilibrium part 4 post-module assessment states the following: 14. The two air pollutants SO2 and NO2 can react in the atmosphere as follows: SO2 (g) + NO2 (g) ⇌ SO3 (g) + NO (g) Predict the effect of the following changes to the amount of NO when the reaction above has...

Hailey Boehm 2H

Question 12 on the post-module assessment states the following: 12. State whether the equilibrium shifts towards products, reactants, or neither when the given change occurs. CO2(g) + H2(g) ⇌ CO(g) + H2O(g) delta H° = +41.0 kJ.mol-1 i. The amount of carbon monoxide is increased ii. The pressure on t...

Hailey Boehm 2H

What is the difference between pKw and Kw? and in what circumstance would we need to use pKw= -log[H3O+] + -log[OH-]?

Hailey Boehm 2H

In class we looked at the chemical equation N2(g) + 3H2(g)= (double arrows) 2 NH3(g).
Without adding more reactants, how would you increase the yield of NH3(g)? We went over this in class but I did not understand the reasoning.

Hailey Boehm 2H

In class we looked at the chemical equation: N2(g) + 3H2(G) =(double arrows) 2 NH3 (g).
What happens if we: increase N2? increase NH3? decrease H2?

Hailey Boehm 2H

Why does the ratio of products to reactants increase in situations where there are a greater amount of moles of reactant present in a container of an equal volume? Does partial pressure play a role?

Hailey Boehm 2H

What is activity? I understand that we use conc. as an approximation in calculations, but what is the relationship between activity and concentration?

Hailey Boehm 2H

In class we went over an example of equilibrium composition with ATP. The initial molarity of ATP in healthy muscle tissue determined to be 8.435 x 10^-3 mol.L-1. The equilibrium conc. of ATP in dead muscle tissue was determined to be 7.214 x 10^-11 mol.L-1. How were we able to find the change in mo...

Hailey Boehm 2H

This question states: "decide whether an aqueous solution of each of the following salts has a pH equal to, greater than, or less than 7. If pH>7 or pH<7, write a chemical equation to justify your answer. .... (e)AlCl3 (f)Cu(NO3)2. I am confused on parts e and f of this question. The answer for...

Hailey Boehm 2H

What exactly is the difference between pKa and Ka? what does each represent and how do you calculate each?

Hailey Boehm 2H

Why do nonmetal oxides produce acids in water? and why do metal oxides produce bases in water?

Hailey Boehm 2H

In my discussion we discussed the name of the compound [Pt(NH2CH2CH2NH2)2Cl2]Cl2. The name is dichlorobisethylenediamineplatinum(IV)chloride. why exactly is the prefix bis- needed? is it because of the name of the ligand ethylene diamine also has a prefix in it?

Hailey Boehm 2H

Question 2D.13 states: Which of these compounds has bonds that are primarily ionic? (a)BBr2 (b) BaBr2 (c)BeBr2 I understand that BBr2 is more covalent due to electronegativity differences, but I am unclear as to why BaBr2 is primarily ionic over BeBr2. Also, how would I be able to determine this wit...

Hailey Boehm 2H

Van der Waals forces are also known as Dispersion/ induced dipole-induced dipole/ and London interactions. All of these terms describe intermolecular attractions that are always present and attractive. They arise due to fluctuating electron distributions, which results in fluctuating dipoles. These ...

Hailey Boehm 2H

In my lecture notes from 11/16, in the pi bond portion I have written down that "pi bonds have e- density on each side of the internuclear axis". What does this mean? and does this have anything to do with the fact that pi bonds do not allow bound atoms to rotate?

Hailey Boehm 2H

A dipole is charge separation. This is reliant on electronegativity. A large enough difference in electronegativity makes a molecule polar. When a molecule has no dipole moments, then it is not polar. A polar molecule has a net dipole (charge separation) because of the presence of opposing charges f...

Hailey Boehm 2H

Yes, I would use the most stable lewis structure for the VSEPR model because the most stable lewis structure will tell you the number of lone pairs that are present for the molecule, and this will affect the molecular geometry. Relying on unstable lewis structures will mislead you in VSEPR.

Hailey Boehm 2H

2E.11 asks you to "use lewis structures and the VSEPR model to give the VSEPR formula for each of the following species and predict its shape"
part d asks you to do this for Xenon Trioxide, XeO3.
Why is the correct molecular geometry trigonal pyramidal? What would this look like?

Hailey Boehm 2H

3F.1 asks you to "identify the types of attractive intermolecular interactions that might arise between molecules of the following substances: (a)NH2OH; (b)CBr4; (c)H2SeO4; (d)SO2" I understand how to determine if hydrogen bonding may arise, but how can you determine whether London forces ...

Hailey Boehm 2H

If you are putting something in increasing order, you use the less than sign, which is <. The sign is always "open" facing the greater value. So, a list of something in increasing order would look like:
x < y < z, where z is greater than y, and y is greater than x.

Hailey Boehm 2H

For the last part of your question, AgF is the only silver halide that is soluble in water. This is because F is the most electronegative element, and the electronegativity difference between Ag and F is the highest of the listed silver halides, and high enough for the halide to have ionic character...

Hailey Boehm 2H

I think I understand the answer to this question but I am not sure how to explain my reasoning. Does anyone know the reason for the decreasing bond lengths in these structures and if it is necessary to draw the most stable lewis structures to determine the answer? Thanks! 2D.13 Place the following m...

Hailey Boehm 2H

Yes, I agree that ionic bonds would be shorter. Generally, we care more about the bond lengths among covalent bonds because there is more variation among the lengths of covalent bonds. For instance, in covalent structures there are single, double, and triple bonds that can form, with single being th...

Hailey Boehm 2H

Yes, it is because of resonance. Electrons are delocalized in resonance structures. For example, Benzene, C6H6 has 3 delocalized double bonds. Lewis structures therefore place limitations on depicting the true e- placement in resonance structures, because they prevent us from depicting the blending ...

Hailey Boehm 2H

Also, to add on, Boron and Aluminum are involved in lewis acid-base reactions. B and Al sometimes can readily form compounds that do not obey the octet rule, but these B and Al compounds can complete their octet when they react with a lewis base. The lewis base donates its e-'s to form a coordinate ...

Hailey Boehm 2H

Yes, I agree with what was previously said about this being another exception. In general, it is more favorable for electrons to fill an orbital (like 3d) than to pack 2 electrons into 4s because it costs less energy for this configuration. This is because a completely filled or 1/2 filled d subshel...

Hailey Boehm 2H

In general for ions, when there is a negative charge you add that number of electrons and when there is a positive charge you add that number of electrons. Then, once you know how many electrons the ion has, you go through the periodic table and start writing the electron configurations beginning wi...

Hailey Boehm 2H

Also, sometimes when referencing the distance between the charges, "d" is notated instead by "r". In short, for multi Electron atoms, there are additional factors that effect e- energy, one of them being the electrostatic potential energy (coulomb) between two charges. These char...

Hailey Boehm 2H

I was also wondering about this. In the atomic spectra video module it says that the equation is v=-R[(1/n1^2) - (1/n2^2)], where n2>n1. This would mean n2 is n initial. However, Mr. Lavelle also recommends to not use this equation because it is really easy to mess up the signs, so you should just u...

Hailey Boehm 2H

In this equation, delta x gives you the range in which the electron can be/ the electron's uncertainty in position, so you would need to divide it in half to get the +/- value. An easy way to think of it is to think of the example that Mr. Lavelle showed us in class where for the H- atom, an electro...

Hailey Boehm 2H

I agree with what was previously stated. Also, from my understanding I think they are used to distinguish between the different orbitals in particular subshell so that we can more easily tell the placement of the electrons in the specific orbitals. ex: 2px^2 2py^1, 2pz^1 is a more specific version o...

Hailey Boehm 2H

The negative sign is there because a bound electron has lower energy than a free electron. When e- is completely removed, E=0. This equation makes 0 a reference point, and indicates that when the e- gets closer to nucleus/lower in orbitals, the e-'s energy is becoming more negative (or in other word...

Hailey Boehm 2H

Technically, they both determine the color of light. C = lamba x v shows how they are inversely proportional to the speed of light, c. Even though they both determine the color of light (they both will tell us essentially the same color on the spectrum), we most often use wavelength to determine the...

Hailey Boehm 2H

Just to elaborate on what others have said, delta p and delta v are the parameters of their respective values. An example in class that Mr Lavelle gave that helped me understand was the example of V = 10 m.s-1 +/- 1. The delta v for this value is 2 because the possible range in which the velocity co...

Hailey Boehm 2H

I prefer to convert mL to L because Molarity is moles/L, as mentioned above. It is only necessary to convert from mL to L if the problem specifically asks for liters or vice versa. Mr. Lavelle usually specifies in the question, so be sure to always to aware of units in your final answer. Hope this h...

Hailey Boehm 2H

Hi! I am going to prioritize the test topics and will probably take questions from the review/ fundamentals HW section to turn in for the discussion on Thursday. This should be helpful because Mr. Lavelle has mentioned how HW problems are included in tests. I am also going to review outline #1 to ma...

Hailey Boehm 2H

The term formula units applies to salts. It refers to the group of ions that matches the formula of the smallest unit of an ionic compound. The salt MgCO3 has one Mg +2 ion and one CO3 -2 ion. You can calculate formula units the same way you calculate the number of object in a sample. Eqn: # of obje...

Hailey Boehm 2H

Yes, you can just simplify the molecular formula because the empirical formula is the simplest positive integer ratio of atoms present in the compound. For example, the molecular formula for butane is C4H10, while the empirical formula for butane is C2H5.

Hailey Boehm 2H

From what I remember a common cause for a change in the number of neutrons in an atom is radioactive decay.

Hailey Boehm 2H

Hi! to further help you with this chemical equation, I think it should look something like this: C14H18N2O5 + 16 O2 = 14 CO2 + 9 H20 + N2. With this equation, it helps to start with balancing the carbon because it is in less compounds on the products side of the chemical equation as opposed to oxyge...

Search found 71 matches