CHEMISTRY COMMUNITY

Arezo Ahmadi 3J

Hi, I was wondering if we include liquid water in rate laws? Question 7.9 from the textbook seems to include water in the rate law, and I was confused by this. Thank you in advance!

Arezo Ahmadi 3J

How does the analysis of the equilibrium constant and the forward and reverse rates of a reaction change if we cannot assume microscopic reversibility?

Arezo Ahmadi 3J

The Arrhenius Theory was mentioned in lecture today to explain how reactions that follow it have linear plots with slope M=-Ea/R, but what is the Arrhenius Theory specifically?

Arezo Ahmadi 3J

In lecture today (03/08), a graph was shown for the Arrhenius equation in which a higher activation energy had a steeper negative slope than a reaction with a low activation energy. Could some explain why there is a difference in these graphs?

Arezo Ahmadi 3J

When considering the frequency factor in the Arrhenius equation, why is it important to the rate constant that collisions are in the correct orientation?

Arezo Ahmadi 3J

If you use the R constant 8.314 J/mol K, then Ea would be in J/mol. Make sure to be match the units in the equation.

Arezo Ahmadi 3J

Hi, for textbook problems, there are some problems that do want you to use Appendix 2B even though it might not be directly stated.

Arezo Ahmadi 3J

Is it possible to have more than three reactants when determining a general rate law? In lecture today, it was said that n, m, and l are usually used as the exponents for reactants in a general rate law, so does that mean that we wouldn't see more than 3 reactants?

Arezo Ahmadi 3J

In lecture today, it was mentioned that in a reaction where N2 gas is a product, this means that t is close to t=0, but how do we know this? Why does a gas leaving a solution mean that the reverse reaction has a less chance of happening?

Arezo Ahmadi 3J

Is the value of k only specific to a certain moment in point of the reaction at which you are plugging in a certain experiment's values for concentrations? Or is k constant for a reaction in all experiments of that reaction?

Arezo Ahmadi 3J

When do zero order reactions occur mathematically? Is that saying that the exponents that are associated with concentrations are all 0 and thus the concentrations of reactants do not affect the rate law? Or what is the meaning of a zero order reaction?

Arezo Ahmadi 3J

In lecture today, it was mentioned that we will only be looking at the forward reaction, but why was it also mentioned that we need the rates of the forward reaction and the reverse reaction? Which one is the one given for initial rates when looking at concentration tables?

Arezo Ahmadi 3J

Hi, I know that nonmetals are not conductors of electricity, but when considering cell diagrams, are metalloids considered conductors of electricity? Or is it just metals or just specifically d-block metals? Thank you in advance!

Arezo Ahmadi 3J

I was also curious about this question! If there isn't an error, I'm wondering if it has to do with how Enaught of the cell is a negative value, which would indicate a non spontaneous process and thus favors the reverse reaction, meaning the cathode and anode or switch? I'm not sure if this makes se...

Arezo Ahmadi 3J

In today's lecture (02/24) at around 29:07, Dr. Lavelle says that there is a positive E naught value, which is why its a nonspontaneous reaction, but I thought positive E naught values were associated with spontaneous processes? Could someone explain this?

Arezo Ahmadi 3J

Since the coefficient of 2 in front of the product in the equation is applied to the entire product, that means that you have 4 moles of Fe, 6 moles of O, 12 moles of H, and 6 moles of O, and so to balance this out, the H2O in your reactants should have a coefficient of 6 instead of a 3.

Arezo Ahmadi 3J

In lecture today, it was mentioned that having more products than reactants is thermodynamically favorable, as we have learned, but why is it that we should start with more reactants than products when setting up a voltage? What is the outcome if you start out with more products than reactants?

Arezo Ahmadi 3J

I was wondering how, in lecture today, we can tell that when the concentration of Mn2+ is increased, the cell potential is greater than the standard cell potential. Is this apparent from the chemical equation? I'm just not sure how to observe this.

Arezo Ahmadi 3J

Yes, you are correct in that voltage is the maximum cell potential because it is a measure of the maximum cell potential in a battery.

Arezo Ahmadi 3J

On many questions that I have seen with balancing redox reactions, I have seen H+, OH-, and H2O being added, but I'm not sure where these came from or how to add them to reactions. When do you know to add one of these species?

Arezo Ahmadi 3J

Dr. Lavelle mentioned in lecture that you cannot have a negative cell potential, as you would never find a battery with a negative cell potential, so you may be right in your assumption that it would not be possible to have a non spontaneous reaction. At the very least, non spontaneous reactions are...

Arezo Ahmadi 3J

Yes, w = -(Pex)(deltaV) is used for irreversible reactions and w = -nRTln(v2/v1) is used for isothermal, reversible reactions. Hope this helps!

Arezo Ahmadi 3J

In the textbook, there was a question asking us to solve for q at constant volume of an ideal gas. To do this, you just use q(v) = nC(v)ΔT, using C(v)=(3/2)R, which is the heat capacity of an ideal gas at constant volume. C(v) is given on the equation sheet. To solve for q at constant pressure, do ...

Arezo Ahmadi 3J

You can use the equation $\Delta S$ = n*R*ln(P1/P2).

Arezo Ahmadi 3J

You would be looking for steeper slopes when considering that the solid and the gas take less time to heat up, so their slope has to be steeper so that the heating curve would accurately represent those forms getting to the melted or vaporized form, respectively.

Arezo Ahmadi 3J

It is important to remember that in reversible processes, delta S total is 0 because this process is at equilibrium. However, in irreversible processes, delta S surroundings is 0. So, for a reversible process, the equation of deltaS total = delta S system + delta S surroundings would be 0 = delta S ...

Arezo Ahmadi 3J

Heat can be thought of when looking at certain conditions. The value of q is more of a general value that accounts for a changing pressure, but enthalpy is a form of that heat that is at constant pressure. Hope this helps!

Arezo Ahmadi 3J

You use those equations that include values for Cp and Cv because these are the specific heat capacities that account for the pressure or volume being held constant, respectively. The values for Cp and Cv can be found on the constants sheet, and you can proceed with the rest of the values given in t...

Arezo Ahmadi 3J

You can relate Gibbs free energy and the equilibrium constant through the equation \Delta Gnaught = -RTlnK which is derived from the equation deltaG = delta G naught + RTlnQ, where Q is the reaction quotient and K is the equilbirum constant. The first equation is true when there is equilibrium, as d...

Arezo Ahmadi 3J

Yes, there should be some irreversible processes that could be isothermal. I'd also be interested in knowing what some examples are of this, though.

Arezo Ahmadi 3J

Standard temperature and pressure is 25 degrees C or 298 K and 1 atm, respectively, which should be able to be assumed if you are not given any other conditions instead.

Arezo Ahmadi 3J

Can entropy change as a result of reactions in an isolated system? Since heat and energy cannot be exchanged between an isolated system and its surroundings, what happens to the entropy of the surroundings?

Arezo Ahmadi 3J

I am still confused about how we can take values for T1 and T2 to calculate an isothermal process as shown in today's lecture (Lecture #14). Aren't isothermal processes held at a constant temperature? Is there a difference between T1 and T2?

Arezo Ahmadi 3J

Adding onto what has already been said about using 8.314 J/mol*K, make sure to always write out the units of your values because even if you do not remember which R value to use, the units can really help you identify which R value will work out.

Arezo Ahmadi 3J

I think your placement is correct, but the question wants the spontaneity to be placed in the above boxes rather than the bottom. However, your understanding of spontaneity and the relationship between Q and K is correct.

Arezo Ahmadi 3J

Reversible reactions do more work, actually, which means that they are more efficient because there's more work for biological systems to use. Irreversible reactions are useful for speeding up some other reactions though which is a benefit of them being fast. However, reversible reactions do more wo...

Arezo Ahmadi 3J

The equation delta U = delta H - P*deltaV represents the equation for change in internal energy, demonstrating that deltaH is enthalpy change and -P*deltaV is the equation for work. Yes, this equation can be rearranged to find a missing variable. If you were given the change in internal energy and w...

Arezo Ahmadi 3J

Since isolated systems do not exchange heat or energy with their surroundings, this is why energy is held constant, and since its value does not change, delta U is 0. An example could be a bomb calorimeter, since a bomb calorimeter is an example of an isolated system that cannot exchange energy with...

Arezo Ahmadi 3J

In today's lecture (02/01), it was mentioned that for the problem with the exothermic reaction (deltaH= -50kJ), an open beaker means constant pressure, but I was wondering how we could arrive at this conclusion. I thought that open beakers would engage more with the surroundings which can affect pre...

Arezo Ahmadi 3J

I am still a bit confused on the application of where the infinite number of steps applies to in the integral equation for w. Why does a infinite number of steps mean that there is a reversible change?

Arezo Ahmadi 3J

I believe it should be the change in the volume of the solution because that is the system that we are measuring the initial volume from, and then when the gas is emitted, we measure the final volume to recognize the difference after the reaction.

Arezo Ahmadi 3J

You can also identify that a process is reversible if the internal pressure and external pressure are equal.

Arezo Ahmadi 3J

Hi, I was wondering if the equation that was used in lecture today, w = -PdeltaV, is for irreversible or reversible changes in the system?

Arezo Ahmadi 3J

I was just wondering if there will always be a negative sign in the equation w = -PdeltaV, since I know that expansion is work done by the system and thus should be negative, whereas compression is work done on the system and therefore work would be positive. Would it always work out if the negative...

Arezo Ahmadi 3J

I was doing the exercise 5G.2 part (b) in the textbook, which is a True or False statement saying: The equilibrium concentrations will be the same whether one starts with pure reactants or pure products. I wasn't sure if this was true or false because I know that it can still reach equilibrium, but ...

Arezo Ahmadi 3J

I was wondering what the difference between an extensive property and an intensive property is. I was not sure why extensive properties are not useful as opposed to intensive properties such as specific heat capacity and molar heat capacity. Could anyone explain this?

Arezo Ahmadi 3J

In lecture today, it was mentioned that there are three terms: heat capacity, specific heat capacity, and molar heat capacity. Will we ever be using heat capacity, or are we going to be focusing more on specific heat capacity and molar heat capacity? Do these differences arise from extensive propert...

Arezo Ahmadi 3J

Hi, I believe the -2.9 kJ value is different from the -2900 J value because of the units. -2900 J must have been converted into kilojoules by dividing by 1000. In the equation, the value for specific heat capacity that was used was in J/degrees C x g, which would result in a Joules answer for q, but...

Arezo Ahmadi 3J

We should not assume that there is a perfect system, but in the concepts and the problem that we solved in lecture, using the concept of a perfect system allowed us to make the connection for the equation q(system) + q(surroundings) = 0, because this equation shows that whatever heat is absorbed by ...

Arezo Ahmadi 3J

The temperature used in the equation is +6.9 degrees Celsius because in the equation for q, which is mass(specific heat capacity)(deltaT), delta T is involved. Delta T is the change in temperature, so it is final temperature minus initial temperature. In the problem, we are given that the final temp...

Arezo Ahmadi 3J

For questions 6D.15 and 6D.17, you need to refer to Tables 6C.1 and 6C.2 to find Ka or Kb values. You would definitely need the Ka or Kb values in order to solve these problems. For instance, in 6D.15 part (a), you can see that Cl- is a spectator ion, and thus the acid NH4+ is concerned. You can obt...

Arezo Ahmadi 3J

If you had a reaction with an inert gas in it, and you increase the partial pressure of that inert gas, does that affect the equilibrium at all? Like if the inert gas was a reactant, would the equilibrium shift to the products or would there be no change?

Arezo Ahmadi 3J

What is the rule about Ka1 and Ka2 when doing acid equilibrium problems? I read something about Ka2 being less than Ka1, but I'm not sure where this applies and what it is used for. Could you explain the significance of Ka1 compared to Ka2?

Arezo Ahmadi 3J

When given a polyprotic acid, do we have to assume that we need to calculate equilibrium concentrations at the last step when the acid has given off as many H+ as possible? I'm just not sure what to do when I see a polyprotic acid and have to find a value such as pH, since I do not know whether to j...

Arezo Ahmadi 3J

Since it was stated that the temperature is 37 degrees, you would be able to recognize that the Kw value would not be the 1.0 x 10^-14 that we have seen. The value for Kw that is 1.0 x 10^-14 applies to when the temperature is 25 degrees.

Arezo Ahmadi 3J

In addition to what has been explained regarding how to solve the problem, it is also important to remember that you need to use an ICE box because it has been stated that a weak acid is involved, rather than a strong acid. Thus, not all of the weak acid completely dissociates, so an ICE box would b...

Arezo Ahmadi 3J

When bonds are being broken or being formed during phase changes, are these intermolecular forces London Dispersion forces? I know Dr. Lavelle mentioned the hydrogen bonds being re-formed during condensation, but I wasn't sure if it is just Hydrogen bonds or just London Dispersion forces or a combin...

Arezo Ahmadi 3J

Hi, I was just wondering if steam coming into contact with skin results in condensation. When the water vapor hits a skin surface, does the vapor immediately turn into liquids? Are those hydrogen bonds immediately broken? I was just wondering about this event conceptually. Thank you in advance!

Arezo Ahmadi 3J

I think that a state itself might not be a state property, since state properties usually describe conditions at that state, such as temperature and pressure. A state might just be the end result of a pathway, and the conditions surrounding it would be the state properties. From one state to another...

Arezo Ahmadi 3J

When you get the value of pOH, use the equation 14 = pOH + pH, and solve for pH by using pH = 14 - pOH.

Arezo Ahmadi 3J

Yes, in this case you would need the Ka/Kb values or the pKa/pKb values in order to solve these problems. They give it to you in a table in the section as it will help you identify which values you need and help you practice writing the correct equations with the correct products.

Arezo Ahmadi 3J

Yes, as partial pressure can only be measured for gases. With Kc, you are looking at the concentrations of substances, in which case you would omit solids and liquids.

Arezo Ahmadi 3J

For question 6E.1 in the textbook, it asks:

Calculate the pH of 0.15 M H2SO4(aq) at 25 degrees C.

How do we know that we have to write out an ICE box for this table and deprotonate H2SO4? I originally thought that you could just take -log of 0.15 M because H2SO4 is a strong acid. Thanks in advance!

Arezo Ahmadi 3J

Hi, I was wondering about question 6D.15 part (b) in the textbook, which states: Calculate the pH of (a) 0.19 M NH4Cl(aq); (b) 0.055 M AlCl3(aq) My question is how do you write the chemical equation for AlCl3, and how do you find the Ka value? I could not find any Ka values in the textbook tables th...

Arezo Ahmadi 3J

[H3O+] was not included in the equation because when Ba(OH)2 dissociates, it only dissociates into Ba2+ and OH-. Ba2+ is a spectator ion, so it does not affect our calculations. Then, you can use stoichiometry to see that for 1 mole of Ba(OH)2, there are 2 moles of OH-. Thus, we multiply the concent...

Arezo Ahmadi 3J

When water is neutral, that means the concentration of H3O+ and OH- are equal. Since Kw has to be constant, [H3O+] and [OH-] have to be the same value to equal Kw, which is 1.0 x 10^-14. Thus, [H3O+] = 1.0 x 10^-7 and [OH-] = 1.0 x 10^-7.

Arezo Ahmadi 3J

Since Ba(OH)2 is a strong base, Ba2+ is a spectator ion. Spectator ions end up being cancelled out, so that is why it is not included in the Kw equation.

Arezo Ahmadi 3J

For the concept of Le Chatelier's Principle, a reaction that is not at equilibrium is going to want to achieve an equilibrium state, which means that the reactants are going to be used up and the products are going to form. Since reactants are being used up, the change in their concentration is decr...

Arezo Ahmadi 3J

Hi, if the system is compressed, you are increasing pressure and decreasing volume, so you are right! After establishing this, you can look at the number of moles of gas on each side of the equation. Aqueous solutions would not be included in this observation.

Arezo Ahmadi 3J

Usually in the equation, the phases are stated next to the reactants and products. Solids are identified as (s), liquids as (l), aqueous solutions as (aq), and gases as (g).

Arezo Ahmadi 3J

K is the value for the equilibrium constant, which means that it is a value that is specific to when a reaction is at equilibrium. However, Q is the reaction quotient to represent the ratio of products to reactants when the reaction is not at equilibrium. You can compare the value of Q to the value ...

Arezo Ahmadi 3J

Every chemical reaction should have the potential to reach equilibrium given that it has the right conditions to reach the reaction's equilibrium constant. This could depend on things like time, since reactions need time to occur and reach that equilibrium constant.

Arezo Ahmadi 3J

Reactants would have a negative sign and products would have a positive sign for x since reactants are being used up and their change is decreasing, while products are being produced and their change is increasing.

Arezo Ahmadi 3J

If you increase the concentration of products at equilibrium, then that means the equilibrium constant needs to remain constant. Since the number in the numerator is now increased, by Le Chatelier's Principle, we need to increase the number in the denominator too, which represents the concentration ...

Arezo Ahmadi 3J

Since 60% of the hydrogen gas reacted, this means that there is 40% left at equilibrium, so you would have 40% of the initial concentration of hydrogen gas left at equilibrium (which is stated in the problem as 0.400 mol/3.00 L) and thus calculate it from there using the equilibrium table.

Arezo Ahmadi 3J

I know that specifically when the equilibrium constant is 0, we would not see that because of how that would mean the product concentration would have to be 0 at equilibrium, which is not reasonable.

Arezo Ahmadi 3J

When given a reaction with aqueous reactants or products, do we need to first write out the net ionic equation in order to write out the K expression? Or do we just leave the aqueous reactants and products in their original form? Thank you in advance!

Arezo Ahmadi 3J

I was wondering, if a reaction is not at equilbirium, does that mean the concentrations of a reactant and a product would be different between the forward and reverse reactions? I know in lecture today Dr. Lavelle mentioned that it doesn't matter if you are looking at the forward reaction of a syste...

Arezo Ahmadi 3J

You would just not include the solid as is the standard procedure for writing out the equation. Both solids and liquids are not included in the equilibrium constant. You would, however, include the gas and aqueous solution.

Arezo Ahmadi 3J

Anytime that the given heat is negative, you would identify this as an exothermic reaction because heat is being given off. Thus, if heat is being given off, or produced, this means that heat is a product. An increase in the products means that to return to equilibrium, a shift to the left, or a shi...

Arezo Ahmadi 3J

For number 19 in the Chemical Equilibrium Part 3 Post-Assessment, the question asks: 0.482 mol N2 and 0.933 mol O2 are placed in a 10.0 L reaction vessel and form N2O (dinitrogen oxide): 2 N2(g) + O2(g) ⇌ 2 N2O(g) KC = 2.0 x 10^-37 What is the composition of the equilibrium mixture? I understand how...

Arezo Ahmadi 3J

I think that the use of Kc and Kp is there to clarify if you are dealing with concentration or pressure, respectively, whereas K is just a broad term for the reaction.

Arezo Ahmadi 3J

Oh that makes sense! Thank you! Just a quick question, though, so why does Q not change even though more products are being produced? I was just confused by how the reactant/product concentrations stayed the same since we're looking at the reaction immediately after an increase in temperature and m...

Arezo Ahmadi 3J

Hi, Note, it is important to remember the equilibrium constant K is dependent only on temperature. Changes to initial conditions such as initial concentrations, initial partial pressures, or introductions of catalysts do not affect the value of K . When the temperature is increased for the system, ...

Arezo Ahmadi 3J

The only time that K is able to change is with a change in temperature. The problem asks about what happens immediately after an increase in temperature. This means that the reactants/products have not had a chance to respond yet, and their concentrations remain the same as before the increase in t...

Arezo Ahmadi 3J

Hi, I was confused about the reaction quotient component of number 7 from Sapling. The question gives an endothermic reaction and asks "What can be said about Q and K immediately after an increase in temperature?" I understood the second part of the question in which the system would shift...

Arezo Ahmadi 3J

If you draw out the Lewis structure for CO2 and find the hybrid orbitals, I get that the sigma bond for the bond between C and O is (C 2sp, O 2sp^2). But for the pi bond, would it be (C 2p^2, O 2p)? I want to make sure that this carbon part of the pi bond is correct because if carbon is sp hybridize...

Arezo Ahmadi 3J

One of the methods that helps me initially determine if an acid is strong or weak is by referring to the seven strong acids that can be found in the textbook. Since HCN is not one of them, that helps me identify it as a weak acid.

Arezo Ahmadi 3J

Electronegativity is important when considering acidity because the more electronegative an element is, the more electron pulling power it has and thus it can distort a negative formal charge from atoms such as an oxygen in a molecule. Thus, this pull from a highly electronegative element is able to...

Arezo Ahmadi 3J

Yes, both of them can be considered amphoteric because they each have a H+ and a negative charge. This means that they can act as an acid by donating an H+ or act as a base by accepting an H+ and becoming a neutral compound.

Arezo Ahmadi 3J

Just to make sure, are cations from Group 1 and 2 acids? I know that they do not affect pH, and more so for Group 1, but it was mentioned today that the cations Fe3+, Cr3+, Al3+, Cu2+, and Ni2+ act as Lewis acids. What is the importance of this statement?

Arezo Ahmadi 3J

It was discussed that when the solution is more basic as the pH is greater than the pKa, then the weak acid gives off a proton. Is the basic solution itself the weak acid that is being referred to? I thought that bases accept protons, so I'm slightly confused on this.

Arezo Ahmadi 3J

I'm still a bit confused on the pH and pKa example about the biological acid, HA, from today's lecture. Are pH and pKa the same concept describing one acid? Or are there two different acids in this example? Could you clarify the molecules involved and why we have these two different values? Thank you!

Arezo Ahmadi 3J

You can find the dentate number by looking to see how many lone pairs are available in a ligand to bind with a transition metal. For example, if there is only one lone pair that can be donated, then it is a monodentate. Additionally, if there were 2 lone pairs available to be donated, then the liga...

Arezo Ahmadi 3J

In today's lecture, Dr. Lavelle mentioned the -COOH groups in the biological molecules. I was just wondering, when he says that these compounds need to be in the presence of water, does that mean that the entire compounds are not acids until they are placed in water and thus the hydrogen is donated ...

Arezo Ahmadi 3J

I was doing a UA worksheet when I saw that we had to write the formula for this coordination compound: Diamminedichloronickel. It is supposed to be [NiCl2(NH3)2], but does anyone know why the Cl2 is before the (NH3)2? I was going in the order of the name, but why are these two switched inside the br...

Arezo Ahmadi 3J

In today's lecture, Dr. Lavelle mentioned both partial pressure and pH as having effects on oxygen. I understand that if pH is changed, this could have an effect on shape and thus the binding of oxygen, but what is the effect of changing partial pressure? Could you explain why oxygen transport and t...

Arezo Ahmadi 3J

Could someone explain the importance of the porphyrin ligand? I'm not sure what its components are in relation to the myoglobin structure. Is it describing all four of the nitrogen molecules, or something else? Thank you!

Arezo Ahmadi 3J

I was wondering if the order of transition metals in the periodic table has anything to do with their characteristics for biological functions. Dr. Lavelle mentioned today that chromium was one of our earlier exceptions for electron configurations when he was mentioning its biological function, and ...

Arezo Ahmadi 3J

The coordination number is simply the number of bonds that are attached to the transition metal. In an example used in lecture today, [Ni(CN4)]2- has a coordination number of 4.

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