CHEMISTRY COMMUNITY

Sarah Blake-2I

Could someone help me with number 4 on the UA first review sheet? I am a bit confused as to where to even start with this problem. Q4. The overall dissociation of oxalic acid, H2C2O4 is represented below. The overall dissociation constant is also indicated. a) What volume of 0.400 M NaOH is required...

Sarah Blake-2I

What is a salt bridge made up of and what is its purpose?

Sarah Blake-2I

How does diluting a solution effect the Ecell value? This was a question on test 2.

Sarah Blake-2I

When looking at multiple mechanisms and asked to find the rate law and k that matches the desired overall reaction, how do you figure out if the rate law of the proposed mechanism is the same as the actual rate law?

Sarah Blake-2I

How can you tell which half reaction is being reduced or oxidized based on the Ecell value? There was a question like this on test 2 and I am confused as to how you would distinguish this based on just the standard potential value.

Sarah Blake-2I

Thank you Dr. Lavelle for everything. You have been a great professor and I will miss your class so much. Thank you for putting in so much effort into giving your students plenty of resources to succeed in this class. I especially appreciate all of the step up sessions and UA midterm and final revie...

Sarah Blake-2I

Could someone walk me through the pre equilibrium approach for rate laws and when we would apply this method?

Sarah Blake-2I

What is the definition of activation energy/ an energy barrier and what is the importance of that energy? Does it have a numerical value?

Sarah Blake-2I

How do half life calculations differ between zero order, first order, and second order reactions? Also, how would you find the quarter life of a reaction?

Sarah Blake-2I

What equations should we know how to derive in the kinetics section?

Sarah Blake-2I

What is the difference between average rate and instantaneous rate in terms of the equations and calculations?

Sarah Blake-2I

Will we be expected to know how to plot first order and second order reactions or do we just need to be able to recognize what plot indicates a first or second order reaction?

Sarah Blake-2I

Will we need to do any calculations regarding electrolysis and if we do, what would be the steps to achieving the right answer

Sarah Blake-2I

In the equation delta G= -nFE, how doe I figure out the number of moles from the balanced chemical equation?

Sarah Blake-2I

I am not quite sure that the reaction being spontaneous increases or decreases cell potential, but I do know that if Ecell is positive, that indicates a spontaneous process. So the value of Ecell determines spontaneity not the other way around.

Sarah Blake-2I

In class today, Dr. Lavelle was mentioning how to tell if a reaction is first order or second order. What does this mean exactly? Also, when using the rate law, how can we tell the order of the reaction based on our answer? Any help is much appreciated. Thank you !

Sarah Blake-2I

Would someone be able to explain what electrolysis is? Is it always an unfavorable reaction or was that just in the example Dr. Lavelle provided with "plugging a phone into the wall"?

Sarah Blake-2I

In the lecture notes, specifically 2/21/20, Dr. Lavelle briefly went over how Le Chatelier's principle applies to E cell and E standard cell. Could someone explain what he meant? For instance he stated that increasing the concentration of Mn 2+ would make Ecell greater than E standard cell. What doe...

Sarah Blake-2I

When do we add a platinum electrode to the outside of a cell diagram for a redox reaction and what is the reasoning behind adding a platinum electrode? Would it be acceptable to just insert an electrode of the same element in the solid form or must it always be platinum when there is no given electr...

Sarah Blake-2I

Is potential difference the same as voltage? And does Ecell mean potential difference?

Sarah Blake-2I

I have been doing a bunch of practice problems in the book for balancing redox reactions and no matter what I do I do not get the right answer when balancing he redox equations. Could someone help explain when we add H2O to a redox equation, OH to a redox reaction, H+, and more electrons. I thought ...

Sarah Blake-2I

How does a reaction being done in an acidic or basic solution effect the way we write the half reactions for redox reactions? In discussion today we did a few like this where you had to either add hydronium and water or OH and water, and I am just confused on how to do that and why we do so.

Sarah Blake-2I

What exactly is a standard hydrogen electrode and when is it useful to use this as a model for other electrodes?

Sarah Blake-2I

In the book, cell potential is defined as the potential difference associated with a galvanic cell that is working reversibly. What happens if the cell is working irreversibly? Or in the forward direction? Does this have an effect on the equation we use?

Sarah Blake-2I

What does it mean for something to have a high potential difference versus having a low potential difference? How does this relate to delta G?

Sarah Blake-2I

In the equation, delta G = -nFEcell, what does F stand for and would we have to calculate Ecell or will that be a given value?

Sarah Blake-2I

Can someone explain how to read a cell diagram and what the importance of a cell diagram is? I am a bit confused as I was reading through the textbook and am just looking for some clarification. Thanks!

Sarah Blake-2I

Would we be given delta S naught and delta G naught or would we need to solve for these values in a problem and how is that calculation different than just calculating delta G or delta S? Thank you!

Sarah Blake-2I

How can you tell if a compound is going through oxidation vs when it is undergoing reduction?

Sarah Blake-2I

I don't think the order of the compound matters that much, so they probably just switched the order of the carbon and hydrogen for convenience, but it does not change the chemical makeup of the compound!

Sarah Blake-2I

How do you go about balancing a redox reaction and figuring out the oxidation states? Are you just looking at balancing the charges?

Sarah Blake-2I

What is the connection between equilibrium and Gibbs free energy and in what scenario would it be helpful to utilize this connection?

Sarah Blake-2I

What is the purpose and meaning of the Van't Hoff equation? And when would we use it instead of the normal Gibbs Free Energy equation?

Sarah Blake-2I

Sometimes it will be given to us in the problem, and other times we will have certain key information that will clue us in on whether there is constant pressure or not based on the context of the problem. For instance, if the problem is talking about a bicycle pump, pressure is not constant and woul...

Sarah Blake-2I

A closed system has a fixed amount of matter but it can exchange energy with the surroundings whereas an isolated system can exchange neither matter nor energy with the surroundings.

Sarah Blake-2I

You might get a problem where you are given an initial and final concentration. In that case, you could solve for the change in x. Otherwise, the ice table calculations will not change.

Sarah Blake-2I

When using delta S = q/t, why can we use change in enthalpy (delta H) over T as well? Also how do you just calculate delta H? The solutions manual is showing that you do the moles multiplied by another value that you look up, but I am not sure what the meaning of that value is. An example of what I ...

Sarah Blake-2I

We can use Hess's law because enthalpy is a state function, which means we can sum the enthalpy values to find the total enthalpy of the new chemical equation.

Sarah Blake-2I

When finding the total enthalpy of the reaction and you can use the method of standard enthalpies of formation, do you multiply each enthalpy of formation value by the stoichiometric coefficient?

Sarah Blake-2I

For 4D.23 in the homework, you have to calculate the standard enthalpy of formation of dinitrogen pentaoxide from the given information: 2NO(g)+O2(g)→2NO2(g)ΔHo=−114.1kJ 4NO2(g)+O2(g)→2N2O5(g)ΔHo=−110.2kJ and from the standard enthalpy of formation of nitric oxide, NO (see Appendix 2A). I am just be...

Sarah Blake-2I

Are there any clues that allow you to see what equation to use in a thermodynamics or enthalpy question? I find myself looking at the problems in this unit completely unsure of what the first step is in calculating and solving these thermodynamics problems. Any help would be much appreciated. Thanks!

Sarah Blake-2I

When do we use degeneracy and what is its relevance to the thermodynamics section?

Sarah Blake-2I

In what context do we need to use integrals and calculus to solve a thermodynamics question and what are we finding when we take the integral from volume 1 to volume 2?

Sarah Blake-2I

What is the difference between reversible expansion and irreversible expansion and what concept does this effect in thermodynamics?

Sarah Blake-2I

Could someone go over the thermochemistry and thermodynamics equations and when we would use each one? Dr. Lavelle gave a bunch of equations for different problems and conditions, but I am confused on what they all mean and when it would be appropriate to use them.

Sarah Blake-2I

Heat is the transfer of energy that occurs with an increase in temperature. Enthalpy, however, is the change in heat at constant pressure. Enthalpy is also a state function. Both occur when there is work being done to the system.

Sarah Blake-2I

I know we haven't covered thermodynamics yet, but could someone explain the difference between thermochemistry and thermodynamics? Thanks!

Sarah Blake-2I

What does it mean that a state property is not dependent on the path taken to obtain that state? Also, why is work not a state function? Both of these were mentioned on Wednesday's lecture :).

Sarah Blake-2I

Do you use standard reaction enthalpy when the reactants and products are in the same phase? I am a bit confused as to what it means to be in the same state.

Sarah Blake-2I

When using method #2, how do you figure out which bonds are broken and formed just by looking at the lewis structures?

Sarah Blake-2I

How do we decide what method to use when calculating reaction enthalpies? Does it depend on the information given in the problem or is there one method that is more exact than the others?

Sarah Blake-2I

Could someone explain to me what a state function is and why that is important? I know enthalpy is a state function but I am not sure why and what its significance is. Thanks!

Sarah Blake-2I

If you are given the moles of a compound and the volume, I know you do moles/liters to find molarity. However, if the compound has a stoichiometric coefficient in the equation do you need to use a molar ratio to find molarity to then use in a Kc calculation? Here is a question where I ran into this ...

Sarah Blake-2I

This is just a general question, but when can we pick up our 14A final exams and where? I thought it was this week but I have also heard it is next week so if anyone has gotten theirs or knows exactly when we can pick them out please let me know!

Sarah Blake-2I

The 5% rule refers to the acceptable percentage of x in relation to the initial amount that makes it okay to approximate the percent ionization with weak acid and base calculations.

Sarah Blake-2I

Yes you should memorize the common strong bases and be able to recognize weak acids and bases, however it is more important to just know the strong ones. Then when you are finding a pH of a weak base or acid, you will need to use an ICE table.

Sarah Blake-2I

In question 5.35, you are given a graph for A, B, and C. You are asked to write an equation and calculate the k value. I am just confused as to how I would find the exact partial pressure values for the K equation just by looking at the graph. I am unsure how to add the graph onto this post but the ...

Sarah Blake-2I

What is the significance and meaning of a pKa value when looking at weak acids and bases? I understand what the Ka value means and I know that pKa is the -log of Ka, but what is the importance of that value?

Sarah Blake-2I

Is water the only molecule able to undergo autoprotolysis or are there other examples of compounds that can be classified under this type of interaction?

Sarah Blake-2I

From what I can tell, there should be 3 sig figs as that is the minimum amount of sig figs used in the problem. Perhaps the book made a mistake and used two sig figs by accident.

Sarah Blake-2I

I was wondering the same thing. I think that if all of the reactants and products are gases, the book will just write it in partial pressure, but I do not believe it matters since the question does not specify whether or not you will be given concentration or a pressure value.

Sarah Blake-2I

K is constant only at the same temperature. If the temperature changes, you will get a different K value, because the energy being absorbed changes as well as the rate of reactants and products.

Sarah Blake-2I

Can someone explain why taking away product leads to more product? I am just a bit confused on that topic.

Sarah Blake-2I

I know we do not include solids or liquids in the Kc calculation but do we also not include aqueous solutions? Could someone clarify this for me?

Sarah Blake-2I

What does it mean for a reaction to be at equilibrium? Does that mean that there are equal amounts of reactant and product once it hits equilibrium or does it just mean that it is going to products and reactants at an equal rate?

Sarah Blake-2I

When writing out the Kc or Kp, how do we know when to show the values in brackets (concentration) vs using P and a subscript of the element. What I am trying to ask is do we only write the values in brackets if we are calculating Kc?

Sarah Blake-2I

It all just depends on what information is given in the problem. If they give you pressure values then I would assume that the concentration would be a different value than the pressure value thus making Kc and Kp different values.

Sarah Blake-2I

The energy level is implied and yes you are correct there would be a 2p in front of the hybridization if it fills up the additional orbital, such as the case with NO2.

Sarah Blake-2I

That just means that the O is bonded to the metal ion instead of the hydrogen. It is written like that to emphasize how it bonds to the metal!

Sarah Blake-2I

Look at each part of the chemical formula and break it down. I like to name the individual atoms or ligands and then after I get the names, I follow the procedure of putting them in alphabetical order and deciding the charge of the metal ion. Looking at the entire compound as a whole can be overwhel...

Sarah Blake-2I

We do not need to know isomers for the final.

Sarah Blake-2I

Is there a difference between saying ammine with two "m's" versus amine with one "m" when naming ligands? Do both refer to NH3?

Sarah Blake-2I

Can someone explain the difference between amphoteric and amphiprotic? What is the difference and what topic does this apply to?

Sarah Blake-2I

Could someone walk me through how to write out an equation to find out if the solution is acidic or basic? For instance KF in water. How would you write the chemical equation for this and how do you know if it will produce hydronium or hydroxide?

Sarah Blake-2I

Will we need to know how to do the calculations in box 6E.1? The directions are slightly confusing and I do not remember this from lecture. Thanks!

Sarah Blake-2I

In section 6D.3 in the textbook, they talk about how to decide whether the solution of a salt will be acidic, basic, or neutral. I was a little lost when they explain it in the book, so could someone further explain this concept to me? And will we need to do problems regarding this concept for the f...

Sarah Blake-2I

Could someone explain the concept of oxoacids? Does more electronegativity result in a stronger acid due to this concept or is it part of the concept of oxoacids? This is from 11/27 lecture.

Sarah Blake-2I

What are some common examples we would need to know for the final for strong/weak acids and bases? How do you tell if an acid or base is strong or weak?

Sarah Blake-2I

What does it mean to have a compound outside of the coordination sphere and how does that compound come into play when drawing the structure?

Sarah Blake-2I

What is the difference between Bronsted acids and bases and Lewis acids and bases? WOuld you be able to tell the differnce in the way they are written out?

Sarah Blake-2I

What is a polydentate? Does it have to do with ligands and the naming of them? I just need some clarification as I am a bit confused with this unit and topic. Thanks!

Sarah Blake-2I

Can someone explain what a chelate is and how to draw them?

Sarah Blake-2I

Could someone run through the steps of naming a coordination compound. I’m confused on how to get the full name and what gets shortened and what stays in its full name.

Sarah Blake-2I

Is the homework that we turn in week 9 or 10 from this section only or does it also include hybridization?

Sarah Blake-2I

I think you just need to know what Lavelle went over in lecture. Basically the amount of electron density in a molecule is how many orbitals will be used, so if the molecule has 3 areas of electron density, 3 orbitals need to be used. It will be sp2 hybridized due to the way we put together the orbi...

Sarah Blake-2I

Hi! Could someone explain why the cis model in today's lecture is what forms the chemotherapy drug cisplatin? I was a little confused during the explanation of this in lecture.

Sarah Blake-2I

I believe CO should have dipole-dipole interactions since there is a difference in electronegativity between C and O. The O will have a partial negative charge and the C will have a partial positive charge, thus forming a dipole. This dipole does not cancel out, which means the molecule is polar and...

Sarah Blake-2I

It all depends on the lone pairs and how many regions of electron density there are in the molecule. AX4E with 4 bonds and 1 lone pair will be see-saw not tetrahedral due to the presence of the lone pair. Tetrahedral is just AX4 with no lone pairs. AX3E2 with 3 bonds and 2 lone pairs would be t-shap...

Sarah Blake-2I

I do not think we need to know this for the test. Just know what pi and sigma bonds are and how they relate to the molecule in terms of strength and properties (pi bonds make the molecule rigid). Their location and whether or not they are parallel or perpendicular shouldn't matter for the test, but ...

Sarah Blake-2I

You are correct in the order of the forces. I think the numbers he gave us in class were not related to strength of the forces but rather the energy of the forces. Since we do not need to know those values, I would just put those to the side and go off of the fact that dipole-dipole is greater than ...

Sarah Blake-2I

Whenever there is a difference in electronegativity that is noticeable, there will be a partial negative and partial positive charge. So for instance, let's look at CCl3. Cl is very electronegative in comparison to carbon. This will cause the Cl to form a partial negative charge and C to form a part...

Sarah Blake-2I

Does a nonpolar molecule have dipole dipole interactions such as AsF5?

Sarah Blake-2I

Dipole moments occur when there is a large difference in electronegativity between the atoms. The more electronegative atom is said to have a partial negative charge and the less electronegative atom will have a partial positive charge. The arrow that signifies a dipole moment is drawn from the part...

Sarah Blake-2I

Can someone give e a brief explanation on sigma and pi bonds. What are they and what are we expected to know about them and their properties? I read the textbook chapter on them and did not get much clarity on what exactly they are. Thank you!

Sarah Blake-2I

For instance, CH3CH2OH. How would I know how to draw this compound?

Sarah Blake-2I

How would you distinguish whether a molecule is linear or bent? Does it have to do with lone pairs or polarizability or something else? I am just a little confused on how you figure out the shape.

Sarah Blake-2I

We will need to memorize the bond angles of the general shapes, but not exact values for specific compounds. You should just know how to determine whether bond angles will be larger or smaller than expected.

Sarah Blake-2I

You must memorize the bond angles for the various shapes, but if dealing with lone pairs, that will cause the bond angle to be less than expected because the lone pairs will cause the atoms to be closer together.

Sarah Blake-2I

Are there any tricks to drawing more complicated lewis structures? I keep drawing them incorrectly and I am not sure how to tell where the bonds go and what is connected to each atom.

Sarah Blake-2I

Can someone explain how you can determine what the shape of a molecule is if it has lone pairs. For instance, what makes something seesaw shaped? I am just a bit confused.

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