CHEMISTRY COMMUNITY

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Are we expected to know how to come up with the half reactions for reactions such as those in 14.13 part D and 14.15 part A (6th edition)?
Or can we only get the half reaction if the appendix is given?

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Why is the slope, k, of second order reactions positive?

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You use the Arrhenius equation for this problem. ln(k2/k1) = Ea/R(1/T1-1/T2)
Given:
Ea = 38 kj/mol
k1 = 1.5E10 L/mols
T1 = 298 K
k2 = ?
T2 = 310 K
lnk2 = ln(1.5E10) + (38/.008314)(1/298 - 1/310)
k2 = e^24 = 2.7E10 L/mols

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Remember that the unique rate for aA + bB --> cC + dD is -1/a(d[A]/d[t]) + -1/b(d[B]/d[t]) --> 1/c(d[C]/d[t]) + 1/d(d[D]/d[t]). You are given the unique rate 0.44 mol/Ls. In order to find (a), you set 0.44 = 1/3(d[A]/d[t]), so to solve for (d[A]/d[t]), 0.44 * 3 = 1.3 mol O2/Ls. You do the same for w...

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(a) In order to find the equilibrium constant, you divide the forward rate constant by the reverse rate constant. K = k1/k'1 = 265/392 = 0.676. (b) The reaction is endothermic because the activation energy of the forward reaction is higher than the activation energy of the reverse reaction. In an en...

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When calculating enthalpy using bond enthalpies, do the calculations apply only for gaseous substances? If so, how do you know when to add or subtract the enthalpy of vaporization to change a liquid reactant or product?

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I believe knowing how to solve integrals and derivatives are mainly for us to know how to derive certain equations in this class. So far, we have been using integrals and derivatives to get formulas such as that of work of an reversible, isothermal reaction, change in entropy, work of a system with ...

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You divide what you got in part (a) by 2 because there are 2 mols of NO2 in the reaction. Another way is you can also divide (b) by one because there is one mol of O2 formed. You divide the rate of reaction by the stoichiometric coefficient to get 3.3e-3 mol/Ls. If you have aA --> bB + cC, the uniqu...

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For this problem you will use the equation E = Ecell - (RT/nF)ln[K]. In this problem, you would look at it as E = Ecell - (RT/nF)ln[(Kout)/(Kin)] Because both half cells are identical, you should expect Ecell = 0. In order to find the range, you have to first calculate how E would be when ions are 3...

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Whichever ion undergoes oxidation is the anode and whichever ion undergoes reduction is the cathode.

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A compound is stable if the delta G of the reaction is < 0. This means that the reaction is spontaneous and proceeds to the forward reaction so the products are stable. A reaction is unstable if delta G > 0. Stability and unstability are related to the tendency of a reaction to decompose into its el...

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We know that Cu/Cu2+ is the anode. The standard potential for Cu/Cu2+ which can be found in the Appendix, is +0.34.
You plug this into the E(cell) = E(cathode) - E(anode) equation to find the potential for the cathode, M2+/M.
E(cathode) = E(cell) + E(anode) = -0.689 + 0.34 = -0.349 V.

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Will we need to know for the test how to derive the equilibrium constant for a reaction given electrochemical data? (Section 14.8 in the textbook)

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Remember that in a reversible reaction, any small change in a variable, such as pressure, of the system will cause a similar change in the surroundings so that there is essentially no change in internal energy. ( U = 0 ) Because in part b the pathway is irreversible, this means that any change in va...

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Does changing the concentration of a substance in a reaction affect the free energy?

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How does free energy change with temperature when the value of enthalpy is negative and entropy is negative?
How does free energy change with temperature when the value of enthalpy is positive and entropy is positive?

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For this problem, you have to calculate the enthalpy of fusion (ice melting) and the heat of the water to determine how much needs to be supplied in total. The enthalpy of fusion, delta H, can be calculated using the value from table 8.3. Convert 80.0 g H20 to moles and multiply it with the enthalpy...

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So with this question, you want to find q of both the copper and the water and add it together to find the total amount of heat supplied. You know that q = mCdeltaT q(copper) = (500 g)(0.38 J/gC)(100-22 C) = 14.82 kJ q(water) = (400 g)(4.184 J/gC)(100-22 C) = 130.54 kJ q(total) = 14.82 + 130.54 = 14...

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You should plug it in as -0.3+√(0.3^2 - 4(1)(-0.6)) and divide it all by 2. You should get a positive number inside the square root and x = 0.137.

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Are we required to know the equipartition theorem?
I'm also confused about the translational, rotational linear, and rotational nonlinear equations that go along with it.

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In this problem, you add the enthalpy of fusion, heat absorbed by ice, and heat released by water. In order to find the enthalpy of fusion, you convert 50.0 g H20(s) to mol and multiply it by the enthalpy of fusion. This would be 2.775 mol H20 * 6.01E3 J/mol (convert kJ in textbook to J). The heat a...

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An open system is one in which matter and energy can exchange with the surroundings. A closed system is one in which only energy can exchange with the surroundings. An isolated system is one in which nothing can exchange with the surroundings. For example, an open system can just be a cup of hot wat...

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I'm assuming mostly like no. We learned lewis structures in 14A so I think they expect you to be able to know which bonds would be broken or formed.

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For this problem, they are just asking you to compare the differences between the bond enthalpies of benzene. In one structure, you have benzene with 3 C-C and 3 C=C bonds. Using the table, this would mean (3*348) + (3*612) = 2880 kJ. However, benzene in its resonance structure has 6 C-C/C=C bonds (...

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Do we apply the rules of sig figs when calculating enthalpy?

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What is the difference between heat and work? How do they relate to internal energy?

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You can use either one.

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The solution is just writing out the chemical equilibrium constant in the form of Kp rather than Kc. They are interchangeable for gases only. When writing it with P subscripts, this indicates that it is Kp, with the equilibrium partial pressures of products on top divided by the equilibrium partial ...

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The increase in temperature depends on whether the reaction is exothermic or endothermic. If a reaction is endothermic, an increase in temperature will make it proceed to the right and produce more products. This means the reverse reaction is exothermic, so a decrease in temperature will make it pro...

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From Chem 14A, we had to memorize which acids were strong and what categorized bases as strong. Strong acids: HCl, HI, HBr, H2SO4, HNO3, HClO4 Strong bases: Most of Group 1 and 2 metal hydroxides If you know those, then everything else should be a weak acid or base. However, I would assume in the qu...

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How does partial pressure and concentration of oxygen affect hemoglobin and oxygen exchange?

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In this problem, we are taking into account of exothermic and endothermic reactions. The reaction shifts toward the endothermic reaction. If a reaction is endothermic, it will have a positive delta H, meaning that increasing temperature will favor the forward reaction and product formation. If a rea...

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Delta H basically means the change in enthalpy, or in other words, the change in "heat". When delta H is positive, it means the products in the reaction have more energy compared to the reactants, so the reaction has gained energy, making it endothermic. When delta H is negative, it means ...

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The answer is 1.58E-8. In order to do this problem you convert 17.4 mg CO2 to moles and divide by 0.250 L to get the equilibrium molarity concentration of CO2, 1.58E-3. Since NH4(NH2CO2) is a solid, it's not included in the equilibrium constant, so you have K = [NH3]^2[CO2]. Because you have two mol...

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On the ICE table, you have to find initial molar concentration, change in molar concentration, and the equilibrium molar concentration. Since you are initially given 1.0 mol/L NO, the change would be -2x since you have the coefficient 2NO in the reaction. In order to calculate equilibrium, you subtr...

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Hello! I'm stuck on question 11.45 part b. (a) A sample of 2.0 mmol Cl2 was sealed into a 2.0 L reaction vessel and heated to 1000. K to study its dissociation into Cl atoms. Use the info in Table 11.2 to calculate the equilibrium composition of the mixture. (b) If 2.0 mmol F2 was placed into the re...

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Yes; since you aren't given any numerical equilibrium molar concentrations, the question just asks for you to set it up.
So basically it would be Kc = [products]/[reactants] raised to the power of their stoichiometric coefficients.

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For (c), en is a bidentate, so it has two binding sites. (en)2 = 4 binding sites total + 2 binding Cl = 6 ligands total, so the coordination number is 6. For (d), edta is a hexadentate, so it has six binding sites, making the coordination number for Cr to be 6. More info can be found in section 17.6...

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Yes, ligands should be written in alphabetical order, ignoring the prefix that indicates the number of each one present.
For example, in that particular compound, "ammine" comes before "sulfato" in alphabetical order, so NH3 is written first.

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Hello!

I'm a little confused as to when we name coordination compounds with bis, tris, tetrakis, etc.
What's an example of when this is used instead of di, tri, tetra, etc.?

Thank you!

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Hello! Question 12.15 in the 6th edition asks to write the Lewis structure of each reactant, identify the Lewis acid and the Lewis base, and then write the Lewis structure of the product for the following acid-base reaction: (b) Cl- + SO2 --> I'm a little confused on this one, because I thought SO2 ...

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Water has a bent shape and this makes it a universal solvent because the positive and negative ends are furthest from each other. Since the H atoms give off a positive charge and oxygen gives off a negative charge, molecules of either charge are able to attract to water. Water's polar covalent chara...

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Yes, in this case N would be sp3 hybridized. When a lone pair of electrons are localized, they are considered in hybrid orbitals.
However, in the case of resonance structures, delocalized electrons in the resonance structures are not counted in hybrid orbitals.

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What exactly is covalent bond dissociation energy and how does it relate to atomic radius, bond multiplicity, and lone pairs in bonding?

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What's the relation between polarizability and electronegativity?

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I believe lone pairs on non central atoms would affect the polarity of the molecule and create a dipole, but it shouldn't affect the overall shape of the molecule. For example, with CH2F2 has a tetrahedral shape. However, F has lone pairs. This would just mean that the molecule is polar, but the sha...

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Hund's rule states that one electron must fill each orbital first with a parallel spin before it can fill up with two electrons in each orbital with opposite spins. For example, in a 2p orbital, one electron must fill each 2px1, 2py1, 2pz1, before another electron can fill those orbitals. The Paul E...

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Dipoles are unequal pulls of electrons. Induced-dipoles happen in London dispersion forces. What happens is that in an atom with an equal amount of electrons dispersed around, a temporary dipole force can occur. For instance, some electrons can temporarily shift to one side, causing one side of the ...

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Formal charge would refer to the charge of each individual atom and the overall number of electrons an atom owns in a molecule. I believe stable charge would just be the most stable form of the entire molecule.

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Resonance is a blending of structures. For example, a nitrate ion lewis structure depicts N as the central atom with bonds to three O atoms. Nitrate has one double bond and two single bonds. The double bond is connected to an oxygen, however, it can be connected to any of the three O atoms. This mak...

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The Roman numerals indicate the charge. For example, this means that Indium has a 3+ charge. We know that sulfur has a 2- charge, so the compound would be made of 2 Indium and 3 Sulfur to cancel out to charges. This results in the chemical formula: In2S3.

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The homework we turn in should correspond to what we've learned in class recently from the past week.

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Elements such as P or S do have open d-orbitals. This is because they have 3s and 3p orbitals already and have available 3d orbitals that can be filled next, allowing them to break the octet rule and have expanded valence shells. On the other hand, this wouldn't work for elements before period 3, be...

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You might be mixing up FC with the overall charge of the ion. I think he said when the formal charge equals 0, that's when it's most stable. In both lewis structures he drew of the sulfate ion, they both resulted in having the -2 charge of the ion. In the first structure with single bonds, each oxyg...

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These questions are basically asking which metal ions with a 2+ charge would have the electron configuration given? The 2+ charge means that 2 electrons were taken away to get the positive charge. For instance, 3.9a) [Ar]3d^7 Add back 2 electrons to get [Ar]3d^7, 4s^2. (Remember 4s fills up before 3...

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Xenon's electron configuration is [Kr]4d^10, 5s^2, 5p^6. The ground state electron configuration for Bi is [Xe]4f^14, 5d^10, 6s^2, 6p^3 because you have to continue off that sequence. The 4f^14 and 5d^10 are from period 6 Lanthanoids and transition metals. It may not show as a single row on the PT, ...

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What I did was that since it says "the meter" was defined as 1650763.73 wavelengths, I divided 1 meter / 1650763.73 wavelengths. I think this should get you one wavelength.

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Light has both wave and photon properties. Wave properties of light explain the inverse relationship between wavelength and frequency of light. It also explains how amplitude represents the intensity of the wave. In this case, bigger amplitude (more intensity light) means greater energy. Meanwhile, ...

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I think in the textbook the h has a line through it. This is a different h value that equals h/(2pi). That's why the h/2 is still equal to h/(4pi). The equation is the same; the notation of the h just makes it appear different.

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The Balmer series has lines with n(1) = 2 and n(2) > 2. It consists of lines that go from n = 2 as well as value anything above that as the second n value. So we know: 656.3 is n = 3 --> n = 2 486.1 is n = 4 --> n = 2 434.0 is n = 5 --> n = 2 410.2 is n = 6 --> n = 2 So now the next one would be : ?...

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So you know that the equation for the hydrogen spectrum is En = -hR/n^2. where R = 3.29E15 Hz. In this case you know that the Balmer series is where there is a transition from any energy level greater than 2 to n = 2. So 656.3 is n = 3 --> n = 2, 486.1 is n = 4 --> n = 2, 434.0 is n = 5 --> n = 2, 4...

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The midterm is Monday, November 5, 6-8pm.
It's on his site under "test and exam schedule"
https://lavelle.chem.ucla.edu/wp-conten ... hedule.pdf

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Part c asks you to find the wavelength of the energy of the photon. In this case, you would use the equation E(photon) - work function = E(kinetic energy), where E(photon) = work function + E(kinetic energy). So from part b you should have found the work function to be 1.66E-17 J. Convert the given ...

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First, I think you mean that the frequency you got is 2.92E15 Hz (s^-1) On page 7 of Section 1.3, there is a figure that shows 102.6 nm is part of the Lyman series, which is on n = 1, so you know that the first energy level is n = 1. In order to find what it transitions to, you can use the equation ...

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I think this question is meant to show that their wavelengths are basically going to be the same. Since they are so close in size, there is very little difference, so you can say they are almost identical.

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The mass of an electron is always about 9.11E-31 kg.

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E(kinetic energy of e-) = .5mv^2.
The mass of the electron will usually be given to you.
The mass of an electron is about 9.11E-31 kg. Plug it in and you should get your answer!

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You know that E(photon) - E(energy to remove e-) = E(kinetic energy of e-). You also know that E(photon) = h(planck's constant) x v (frequency) In other words, hv - work function = (1/2)mv^2 (where m = mass of e- and v = velocity of e-) Mass of e- = 9.11E-31, Given velocity = 6.61E5 This would then ...

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In the photoelectric experiment, light was shone on a metal surface. If the energy of the incoming light was greater than the energy needed to remove the electron (work function), then electrons were emitted from the surface. This way, we are able to measure their kinetic energy.(Ephoton - Ework fun...

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Titrations are when you measure the volume of one solution and see how much you need for it to react with the volume of another solution. For example, think of acid-base titrations. You know the amount of volume of the acid in a flask, but you don't know how much base is needed to react and neutrali...

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1. First you would determine the amount of moles for KCl, K2S, and K3PO4 by dividing the mass given by the molar mass of each compound. In that case, you would get 0.00671 mol KCl, 0.004535 mol K2S, and 0.00236 mol K3PO4. 2. In order to calculate the amount of potassium ions, you would take into acc...

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When you do sig figs for addition/subtraction, only think about the amount of digits after the decimal point. First you would do addition/subtraction normally, then afterwards you would round your answer to the least number of places in the decimal portion of the numbers you added/subtracted. For ex...

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