CHEMISTRY COMMUNITY

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we typically add platinum to either (or both) side of the cell diagram if there isn't already an electrode in it

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The forward reaction will be favored if delta G is negative and vice versa

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We add platinum to a cell diagram when there isn't already an electrode to help transport the electrons

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Will the combustion of gas always be spontaneous?

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When writing a cell diagram, do we leave out H2O? if so, is that the only compound we need to not include if given the half reactions?

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in a given cell diagram, if the pressure of two different compounds is given as 1.0 bar and 1.0 molxL^-1, when we are setting up Q, do we ignore the units or are they the same? (6N.5 part a for reference)

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if a compound appears on both sides of a salt bridge (or the double line), do we not include it in our half reactions? for example in 6N #3 part a and c

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In exercise 6N 1b, why is n=2 and not n=1? More specifically, in the solutions manual, it gives the reduction half reaction as: In3+ +2e- --> In2+
but in appendix 2B, it only shows one electron in the previous equation

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When writing cell diagrams and after having found the cathode and anode half reactions, do we ignore the coefficients of the molecules when putting them into the cell diagram?

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If the cell potential isn't explicitly given, how do we calculate for it? For example, in 6M 3. (a) Pt(s)|Cr3+ (aq),Cr2+ (aq)||Cu2+ (aq)|Cu(s), the cell potential for Cr is not in the tables of potential values provided, so how do we go about problems like these?

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Will the anode always be on the left and the cathode always on the right or does it depend on the compounds involved?

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When an electrolytic cell is missing an electrode, will we always use platinum or does it depend on the other compounds involved?

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When we have a basic solution and want to balance the half reactions, would the compounds we use be different than what we use for an acidic solution? For example in an acidic solution, we first add H2O to balance the oxygens and then add H+ ions to balance the hydrogens.

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If the n in DeltaG=-nFE is not explicitly given, how do we calculate its value?

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How come the oxidizing agents are the opposite of what is being oxidized? and the same for the reduction agents

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the purpose of a salt bridge is to allow electrons to move between the anode and cathode without there being an interruption in the flow

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platinum is the most common electrode for a half reaction that doesn't already have one for the electrons to travel through.

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the flow will go from left to right as it goes from anode to cathode, and another way to look at it is that it is going from negative charge to positive charge

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what compound do we add if we need for O in a basic solution and why?

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which compound do we use if we need more H in an acidic solution?

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Since entropy is a state function, that means the path you take does not matter, so they will technically be the same.

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Even if your value of delta S of the surroundings is greater than zero, the reaction does not have to be spontaneous, but according to the 2nd law of thermodynamics, the process will be spontaneous if delta Stot is a positive value.

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Delta S is equal to the entropy of the system whereas delta Ssurroundings is the entropy of the surroundings and so delta Stot is the entropy of the surroundings and system added together.

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Elements that are in their most stable form, such as H2(g) and Fe(s), will have standard enthalpies of formation equal to zero.

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Since the system is doing work, your value should be negative whereas it would be positive if work was being done on the system

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Since both the forward and reverse reactions are occurring at the same rate in equilibrium, delta G naught would be equal to zero

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Will we need to know the four cases of the effects of temperature for calculating dG along with the graphs explained and shown in 4J.4?

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Will there be any problems on the midterm that requires us to use the Boltzmann formula and to know how to calculate for systems with different numbers of microstates?

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When using the first given equation in the book for calculating the change in enthalpy, dS=qrev/T, do we have to know all three of the listed facts also given in the book?

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Are the values of Delta H of vaporization typically endothermic or exothermic?

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In terms of thermodynamics, expansion is referring to when the volume of a system increases

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One of the main differences is that closed systems cannot exchange mass with its surroundings however it can exchange energy, meanwhile isolated systems cannot exchange either.

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The value of R we use depends on the units of the problem you are trying to solve.

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Delta H would be positive when ice turns to liquid

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Yes, you are correct, we are referring to constant pressure

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Three ways to change the energy of a system include work, mass flow, and heat.

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Cp=5/2R is used when you need to find the heat capacity of an ideal gas with a constant pressure and Cv=3/2R is used when you need to find the heat capacity of an ideal gas with a constant volume

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Since steam releases a lot more energy in comparison to regular boiling water, the burn that the steam inflicts is much more severe than that of the boiling water.

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Why do elements in their standard states have a standard enthalpy of formation equal to zero?

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Why is the temperature change for celsius and kelvin the same? For example, if delta T was 8 for celsius, why is it also 8 for kelvin?

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Dr.Lavelle won't expect us to draw them but he did say that it is quite helpful so it is one way to work through a problem if you get stuck.

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Will a calculation of the enthalpy of vaporization, fusion, or sublimation ever result in a negative value?

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How do you calculate the standard reaction enthalpy if the bond enthalpies are not available? Can you please include an example too

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I believe the second method that Dr. Lavelle covered in lecture that uses bond enthalpies to calculate the total enthalpy is the least accurate method.

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No, I believe Ka and Kb values can also apply to strong acids and bases as well as weak ones.

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If the energy of the products is greater than that of the reactants, then it can be said that the reaction is endothermic.

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There are different values for the constant R but that is only because it depends on the units that are being used, but they will be provided on the equation sheet that is given on the tests.

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How do we make up for a difference in phases when trying to calculate for the total enthalpy? Can you please give an example, thank you!

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Will we have to memorize any of the numbers for the more commonly used elements/compounds?

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Why does a small percentage of initial make the approximation acceptable?

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When trying to calculate the pressure of a substance, is it possible to do so without being given temperature?

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Could somebody explain the quick way to determine a response of equilibria to change? Dr. Lavelle mentioned it in lecture but I hadn't heard of it prior to when he talked about it so I'm still a little confused.

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When calculating Q, how come we include aqueous substances?

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Is it possible to calculate the partial pressure when only given the chemical compound? If so, how?

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When calculating for the reaction quotient, will the partial pressure be given in a problem or do we have to solve for it?

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In the example of potassium hexacyanido ferrate (II), would the suffix for iron be different if the charge on the coordination compound was positive?

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Does the cation always come before the anion? If so, why is that?

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Can there ever be a case in which the resulting anion is not stable?

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Why does a stronger acid have a lower pka value as opposed to a weaker acid?

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When in reference to relative acidity, what does charge delocalization stabilize? Dr.Lavelle mentioned this in lecture but I was not able to hear the rest of the sentence.

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A molecule that is attached to the central metal

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Will we need to be familiar with density isosurface and electrostatic potential surface for the class?

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How can a poly atomic molecule be nonpolar if it’s bonds are polar?

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Why is the energy the lowest if the atoms bounded to the central atom are far from lone pairs?

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If we are able to determine the shape of a molecule with the VSEPR formula, but not the angles, will we need to know how to calculate for the angles?

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Yes, those VSEPR notations are correct and I believe the corresponding shapes would be tetrahedral and trigonal pyramidal (correct me if I am wrong please).

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For a double bond, there is 1 sigma bond and 1 pi bond and for a triple bond, there is 1 sigma bond and 2 pi bonds.

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What does the second vsepr rule tell us?

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Yes, a triple bond has 1 sigma bond and 2 pi bonds whereas a single bond has 1 sigma bond and a double bond has one sigma bond and one pi bond.

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In a triple bond, does it matter the order in which the sigma and pi bonds are?

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The AXE formula is quite helpful in determining the shape of a molecule and the shortcuts Dr. Lavelle taught us is even more helpful.

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While it might not be necessary to draw the molecules, it might be helpful in determining the shape and bond angles of the molecule.

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Since lone pairs result in repulsion of the atoms in the molecule, the geometry of the molecule will be affected.

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I think it would be best to memorize both the bond angles and the shapes, especially for the upcoming test.

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When the dipoles are facing opposite directions, they will cancel out.

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How do we determine the shape of a molecule that has more than one central atom?

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The difference in electronegativity levels will allow you to distinguish what type of bond it is.

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In the case of a triple bond, there should be a single sigma bond and two pi bonds.

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Knowing the quantum numbers of an orbital will allow you to recognize the energy levels of each.

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The number of electrons that a molecule with an expanded octet can have is dependent on the type of element it is.

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What must we take into consideration if we are trying to use double or triple bonds?

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To what extent should we familiarize ourselves with anything concerning dipoles?

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Why are ionic bonds typically stronger than covalent bonds?

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If an element has an odd number of electrons, does it matter which side of the element shorthand we put it on?

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What does an element’s valence electrons determine in terms of its electronegativity?

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I am having a bit trouble understanding the concept behind the quantum number ms. How do we determine this value?

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Why is it that the electrons in covalent bonds are not equally shared?

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Will we have to memorize each kJ.mol^-1 value for the interactions that give rise to attractive forces?

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In what way should we describe the trends of electronegativity?

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In a Lewis dot structure, if an element were to have 4 dots, would we arrange them in such a way that there is one dot on each side of the element shorthand or would we arrange them so that two sides of the element’s shorthand has a pair of dots?

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Since the mass of an electron does not vary depending on the element, it is known to have a set mass of 9.109 x 10^-31 kg, which is also considered a constant.

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Can somebody explain the difference in formation of ionic compounds and forming a molecule because the notes say that both have to do with achieving the lowest energy.

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What does it mean for an electron that is involved in resonance structures to be delocalized?

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Why are electrons that are further away from the nucleus easier to remove?

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Would we have to write out all the p-orbital values or can we keep it simplified? Example: N: 1s^2 2s^2 2px^1 2py^1 2pz^1, or can we just write it as 1s^2 2s^2 2p^3?

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In the example done in class on October 9th, we calculated for the change in energy for the electron and we got a negative answer, however, when we used that value to calculate the frequency of the light, it was positive. Why was wasn’t the negative sign included?

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Why is the threshold energy greater than the activation energy?

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Why does having wavelike properties prevent the electron from collapsing down to the nucleus?

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If we are given a problem where we must calculate ΔE using empirical equation for a hydrogen atom, must we memorize Rydberg’s constant or can we determine the answer by other means?

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Since the intensity of light is proportional to the square of its amplitude, if the amplitude were to increase, so would the intensity.

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