CHEMISTRY COMMUNITY

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In the solutions manual they make it more difficult to see the different steps involved since they combine it all but all you have to do for part (a) is convert H2 and I2 to moles and then convert them to a molar concentration by dividing the number of moles obtained for each by the volume 0.750 L. ...

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I’m pretty sure that’s the only real purpose of it because the equation is meant to be visualized on a graph.

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When Q>K think of drawing a little pac man guy off the greater than sign and his mouth is going towards the reactants so the reaction favors reactants and if Q<K draw the pac man going towards the products side so the reaction favors the formation of products. Silly tip but useful.

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If you are talking about the equation Ka= [H3O+][A-]/[HA] I don’t think it necessarily has to be memorized but if you just think about it like other problems with the equilibrium constant, K, it’s just products over reactants which you can tell from the reaction of the acid you are given.

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In the question you are calculating the standard entropy of vaporization of water at 85 degrees C, given that it’s standard entropy of vaporization is 100 degreees C. The three steps you sum together are: 1. the entropy change heat the reactants to 100 C 2. the entropy of vaporization of h2o at 100 ...

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25 degrees C is usually used in a lot of the problems though since this is just room temperature

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0 degreees celsius

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What number is this in the book?

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You use the Van’t Hoff equation to find the pH based on the information given and then you compare this pH you get to pH 7. If the pH is below 7 then pH would be basic and if it’s above 7 then a pH of 7 would be relatively acidic.

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This is a question finding the standard enthalpies of formation where you look at the bonds broken an formed. For part c) it says 3 mol CRC bonds are formed. What is a CRC bond? also what does it mean when it says “atomize”?

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The more I look at it I think they are actually comparing experiments 1 and 3 which would then make perfect sense. If anyone can confirm this?

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For Question 15.9, I understand how to find the order of A you compare the experiments where the values are the same for [B] and [C] but different for [A] but I don’t get when you are trying to find the order of [B] how to correctly decide which experiments to compare? The book compared experiments ...

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It allows us to analyze the effect of temperature on the rates of chemical reactions

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Can someone please clarify the unique rate of reaction specifically for question 15.3 part c?

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What is the difference in solving a problem that asks for the initial rate vs. one that just ask to find the rate?

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Okay so I just realized the cell potential for Cu is given so then you just plug in:
-0.689 V=E(cathode)-(0.34V)
to get the reduction potential of the anode

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The Question is: A student was given a standard Cu(s)| Cu^2+ (aq) half-cell and another half-cell containing an unknown metal M immersed in 1.00 M M(NO3)2 (aq). When the copper was connected as the anode at 25C, the cell potential was found to be -0.689 V. What is the reduction potential for the unk...

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Gibbs free energy changes with the temperature and pressure of the thermodynamic system. So the point of the van 't Hoff equation is that it relates the change in Keq to the change in temperature, T, when you are given delta H at a constant temperature.

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q is not a state function because the energy transferred depends on the path chosen

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ΔT = 0 so the ΔU = 0 ( for an ideal gas) but Q ≠ 0,
the opposite would be an adiabatic process, ΔT ≠ 0 but Q =0

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The second law of thermodynamics states that the total entropy of the universe always increases for a spontaneous process.

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I know the equation is U=3/2nRT but in one of the homework problems another equation with U=5/2nRT is mentioned. Does anyone know what the purpose of this second equation is for?

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They are given on the constants and formulas sheet so no, just need to know how to correctly apply them.

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It is on the constants and formulas sheet from our last quiz so it would be given to us.

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basically think of it as x is negative for the reactants because these are being used up to form the positive products

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I believe they are the same.

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You use the quadratic equation when u have an x^2 when you set up the equilibrium constant equation. Sometimes you have just an x so you wouldn’t need to do a quadratic you could just solve.

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Basically this principle says that if a gas is added or other constraint than the equilibrium shifts to counterbalance the effect applied

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When looking at a recation, if the number of hydrogens has decreased when going from reactants to products then the substance is an acid (donates hydrogen ions). If the number of hydrogens increases from reactants to products then that substance is the base (accepts hydrogen ions).

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Q changes as the reaction of the system approaches equilibrium versus K that is the numerical value of Q at the "end" of the reaction, when equilibrium is reached. They are the same calculation but different significances.

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You compare the disassociation of the conjugate acid to the conjugate base or vice verse by putting the concentration of the product for example conjugate acid over the concentration of its reactant concentration base times 100%. The picture shows how it is applied for the problem I did at the bottom.

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K is the equilibrium constant and Q is the reaction quotient. K is used when the system is equilibrium and Q is used when the system is not in equilibrium. You can compare K and Q to find out which direction the reaction will proceed.

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Will the reactants always have a negative when doing the c for your ice tables?

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For part a how can you tell which flask is at equilibrium? I know the answer is flask 3 but I just don’t know how to reach this conclusion.

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For Question 4.73, how do lone pairs affect bond angles? Specifically when comparing CH2^2- and CH3^- since they are both less than 109.5 degrees but CH3^- is slightly bigger.

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I’m still struggling with distinguishing if the atom is polar or nonpolar. Judging off of the answers to Question 4.25 is the best way to distinguish if it is polar or nonpolar to see if the Lewis structure looks symmetrical and if so it’s nonpolar and if the Lewis structure isn’t then it polar or i...

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To find hybridization you must determine the number of regions of electron density present. A region of electron density is either a pair of lone pair electrons or a bond (every single, double and triple bonds just counts as one region). The number of regions correspond to a hybrid orbital (s, sp, s...

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Will there still be the Step-Up Session from 5-7 tonight in Hedrick Hall?

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Will we have to do pH calculations on the final using the -log equation based on a concentration we are given? I know there are homework questions concerning calculations but we some UA’s have said there will be calculations on the final while others have said not to worry about it.

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one sigma and two pi bonds

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A region of electron density is either a pair of lone pair electrons or a bond (every single, double and triple bonds just counts as one region). The number of regions correspond to a hybrid orbital (s, sp, sp2 etc.) 1 region - s 2 regions- sp 3 regions- sp2 4 regions- sp3 5 regions- sp3d 6 regions-...

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Every bond has a sigma bond. A single bond has one sigma bond. A double bond has one sigma and one pi bond. A triple bond has one sigma and two pi bonds. They are the strongest type of covalent bond. Basically, it is a more specific way to classify bonds and occurs from the overlapping of orbitals.

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It’s a way to further classify ligands by identifying how many sites the central atom binds to.

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I’m guessing that there would be an arrow pointing to a bond and you would have to identify the type or it would ask how many total pi and sigma bonds there are in a Lewis structure that we would be given a picture of.

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Between these two drawings of Lewis Structures, would it be more favorable to draw the structure so that there is a -1 charge on 2 of the O's and a 0 formal charge on the central atom, S or would it be better for all the O's to have a FC of 0 and then S to have a charge of -2? I’m not sure if there ...

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I’m guessing you are referring to part (a) of 3.59 ? because that is the only one without a full octet but this is because it's not possible to have a full octet on one of the elements since ClO is radical since there is an odd number of total valence electrons for ClO since Cl has 7 valence electro...

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Formal energy aka formal charge is the difference between the number of valence electrons on the free atom minus number of valence electrons assigned to the atom in the molecule. It tells you how reactive the atom is and also it helps you see if you drew your Lewis structure correct because you can ...

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I do not know all the exceptions but elements containing d-orbitals can hold more electrons than the octet rule.
P can hold up to 10 electrons.
S can hold up to 12 electrons.
B, Al- 6 electrons.

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This just means that they fill the octet for however many valence electrons they require without going over so if an element only has four valence electrons than this is "as far" as it can go towards completing the octet.

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You just look at the periodic table and count what position the element is in in the row (excluding d block). For example: Oxygen has 6 valence electrons and Flourine has 7 and Carbon has 4 valence electrons.

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As you move across the period the atomic radius gets smaller and as you move down the column the radius gets bigger. So silver has a larger atomic radius than zinc. This is because when you add a proton, then the nucleus pulls the electrons in stronger, pulling the atoms cell close to the nucleus. S...

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In the Heisenberg equation you are solving for the uncertainty (indeterminacy) in position, mass, or volume based on the information the question gives you and you solve to find the amount for the variable that is equal to or just above the amount h/4(pi) so it doesn't make sense to solve for the ma...

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There is no way to tell from just looking at the periodic table because they have been found to be exceptions through experimentation. The only ones I believe that we need to know for the test are Cu and Cr like Dr. Lavelle said, it is also easy to remember that Gold and Silver are too.

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It is usually always best to automatically convert to L in most problems when you see mL since this is the unit the answer needs to be in for most problems. This question does not specify the units the answer has to be in so since the question gives the volume in mL it is just easier to find the ans...

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The size of an atom changes depending on the size of the nucleus and how much energy each electron has. An element’s location on the periodic table affects the size, thus the radius changes so if you were to calculate the energy of the electrons you would know that the radius has changed.

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The Schrondinger equation basically helps us find the equation's wave function. Once we know this then we can find the quantum numbers and shapes of the orbitals that characterize electrons.

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Each orbital in a su shell has a different shape characterized by a different letter (s, p, d,f). They have electrons with different angular momentums so this sets them apart from each other.

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This is because the Bohr model only works with hydrogen. It does not correspond to other energy levels, so these other energy have different properties than the first. Since hydrogen atoms have only one electron, they contains a large number of shells, thus when one electron jumps from one shell to ...

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Since you are given the wavelength you can solve for the frequency since the c in this equation is a constant c=(wavelength)(frequency). Then the Energy equation is E=h*(frequency). Since you just found frequency and h is a constant then you can solve for the energy. Or you can simply just use the e...

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If you were to look for the de Brogolie wavelength of a macroscopic object it would be tiny since in this equation h, Planck's constant is already very small and then then macroscopic object's mass which would be m is way bigger than the mass of particles that de Brogolie's equation usually deals wi...

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I’m sure on tests he will give us the names to complex compounds but I think this really just comes with practice and the more you become familiar with different compounds. If you have some knowledge of the compound you could know that sodium Na bicarbonate is CO3 and there is also an H so it’s NaHC...

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this is the speed of light in a vacuum so this constant is wavelength x frequency

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Avogadro‘s # is the number of particles, atoms or molecules that are in one mole. It can be applied when you have an amount given for moles and the question asks for it in atoms so you use dimensional analysis to convert values.

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Quanta are discrete bundles in which radiation and other forms of energy occur and light is sent out in the different ‘amounts’ (quanta) that called photons.

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I=E/tA
where I is intensity, E is energy, t is time, A is area of the radiation

The reason to find the intensity of radiation is because a surface has different intensities depending on the different direction the surface is hit.

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Basically a simple way to think about isotopes are that within the same element there are atoms that have a different number of neutrons but same number of protons. So the atomic mass within different isotopes changes.

(IsoTopes) T for Top meaning the top number (atomic mass changes)

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In Appendix 1C there is a rule that says to "make sure that the number of decimal places in the result is the same as the smallest number of decimal places in the data." How does this work if one of the numbers you are adding does not have decimal places? For example: 12+ 0.123=

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Can someone clarify what it means in Appendix 1C when it says "In multiplication and division by an interger or an exact number, the uncertainty of the result is determined by the measured value."?

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