CHEMISTRY COMMUNITY

Alyssa Bryan 3F

The rate constant of the first-order reaction 2N2O (g) = 2N2 (g) + O2 (g) is 0.76 s^-1 at 1000 K and 0.87 s^-1 at 1030 K. How do you calculate the activation energy for this reaction?

Alyssa Bryan 3F

What is the difference between the catalyst and intermediate of the reaction?

Alyssa Bryan 3F

Substance A decomposes in a first-order reaction and its half life is 355 s. How much time must elapse for the concentration of A to decrease to (a) one-eighth of its initial concentration; (b) one-fourth of its initial concentration; (c) 15% of its initial concentration; (d) one-ninth of its initia...

Alyssa Bryan 3F

Determine the rate constant for each of the following first order reactions, in each case expressed for the rate loss of A:
how do you determine the rate constant for part c) 2A $\rightarrow$ B + C, given that [Ao] = 0.153 mol/L and that after 115 s the concentration of B rises to 0.34 mol/L

Alyssa Bryan 3F

For part c) determine the value of the rate constant, I get 2.85 as the answer for K not 2.85 x 10^12. How do you get the correct answer and why are the units L^4 x mmol^4 x s^-1 as shown in the back of the book?

Alyssa Bryan 3F

Why is delta G not positive in photosynthesis?

Alyssa Bryan 3F

Write the half-reactions, the balanced equation for the cell reaction, and the cell diagram for each of following skeletal equations:
for part c) Cl2(g) + H2(g) = HCl(aq)
why do both the anode and cathode separate HCl to either H+ of Cl-?

Alyssa Bryan 3F

For each reaction that is spontaneous under standard conditions (K>1), write a cell diagram, determine the standard cell potential, and calculate deltaG for the reaction:
for part b) 2Hg^2+(aq) + 2Br-(aq) = Hg2^2+(aq) + Br2(l)
How do you determine that this reaction is not spontaneous?

Alyssa Bryan 3F

For each reaction that is spontaneous under standard conditions (K>1), write a cell diagram, determine the standard cell potential, and calculate deltaG for the reaction: For part a) 2NO3-(aq) + 8H+(aq) + 6Hg(l) = 2Hg2^2+(aq) +2NO(g) + 2H2O(l) why does the answer in the textbook use O(g) in the cell...

Alyssa Bryan 3F

When using this equation, delta G = -nFEcell, how do you determine the value of moles (n)?

Alyssa Bryan 3F

In the book, each problem tells us whether the reaction takes place in an acidic or basic solution. What is the importance in knowing what type of solution the reaction occurs in?

Alyssa Bryan 3F

What is the difference between being a reducing agent vs being reduced and being an oxidizing agent vs being oxidized?

Alyssa Bryan 3F

The following redox reaction is used in acidic solution in the Breathalyzer test to determine the level of alcohol in blood: H+ + Cr2O7^2- + C2H5OH = Cr^3+ + C2H4O + H2O. When writing the balanced oxidation half-reaction, why can you add 2 H+ to the reaction to get C2H5OH = C2H4O + 2H+ + 2e- when th...

Alyssa Bryan 3F

Initially an ideal gas at 323 K occupies 1.67 L at 4.95 atm. The gas is allowed to expand to 7.33 L by two pathways: (a) isothermal, reversible expansion; (b) isothermal, irreversible free expansion. Calculate delta S total, delta S, and delta S surroundings for each pathway. How would you solve for...

Alyssa Bryan 3F

Suppose that 50.0 g of water at 20.0 C is mixed with 65.0 g of water at 50.0 C at constant atmospheric pressure in a thermally insulated vessel. Calculate delta S and delta S total for the process?
Why is there a difference between delta S and delta S total for this process?

Alyssa Bryan 3F

In part (a), the equation you use to calculate the standard enthalpy of vaporization is delta S (vap) = delta H (vap) / T(boiling point in K). So you get delta H (vap) = (85 J/K)(80 + 273 K) = 30,005 J or 30.0 kJ. For part (b), the standard entropy change of the system is calculated by multiplying ...

Alyssa Bryan 3F

In a reversible process, the direction of the process can be "reversed" in incremental steps while irreversible processes can't be reversed and don't occur in discrete steps. Reversible expansion does more work while irreversible expansion does work against constant pressure.

Alyssa Bryan 3F

Can someone explain the concept of W (degeneracy) and how to solve for it?

Alyssa Bryan 3F

Can someone explain when we use this equation to solve for work w = - P ∆V versus when we use this equation w = -nRT ln V2/V1 ?

Alyssa Bryan 3F

Will we need to know how to use the work equation with the integral on a test or was Dr. Lavelle just explaining the background and giving more information for the other equations?

Alyssa Bryan 3F

Air in a bicycle pump is compressed by pushing in the handle. The inner diameter of the pump if 3.0 cm and the pump is depressed 20. cm with a pressure of 2.00 atm. (a) how much work is done in the compression? (b) is the work positive or negative with respect to the air in the pump? (c) what is the...

Alyssa Bryan 3F

Which gaseous compound do you expect to have the higher molar heat capacity, NO or NO2? How would you determine which compound has the higher molar heat capacity?

Alyssa Bryan 3F

Determine the reaction enthalpy for the hydrogenation of ethyne to ethane, C2H2 (g) + 2H2 (g) = C2H6 (g), from the following data: ΔHc(C2H2, g) = -1300 kJ/mol, ΔHc(C2H6, g) = -1560 kJ/mol, ΔHc(H2, g) = -286 kJ/mol. Why is the answer -312 kJ/mol and not +312 kJ/mol?

Alyssa Bryan 3F

The actual bond enthalpy depends on the neighboring molecules as well, so that is why there are varying values for the other molecules and the average is given.

Alyssa Bryan 3F

For part (c) the concentration of H30+ is 3.1 mol/L. Since [H30+] x [OH-] = 10^-14, I keep getting 3.2 x 10^-15 while the answer in the book is 3.2 x 10^-12. What am I doing different/wrong and how do you get the correct answer?

Alyssa Bryan 3F

Because the equation for the equilibrium constant is K=products/reactants, when K is equal to 1 the amount of products is equal to the amount of reactants at equilibrium.

Alyssa Bryan 3F

Can someone explain the relationship between pressure and volume for Le Chatelier's Principle.

Alyssa Bryan 3F

In 5I.23 7th edition, the problem states that "a reaction mixture consisting of 2.00 mol CO and 3.00 mol H2 is placed in a reaction vessel of volume 10.0 L and heated at 1200 K. At equilibrium, 0.478 mol Ch4 was present in the system. Determine the value of Kc for the reaction CO(g) + 3H2(g) = ...

Alyssa Bryan 3F

Part B of the question says that "if 2.0 mmol F2 was placed into the reaction vessel instead of the chlorine, what would be its equilibrium composition at 1000K." I was able to solve correctly for part A, but I can't seem to get the correct answer for part B. Can someone explain the steps ...

Alyssa Bryan 3F

"In a gas phase equilibrium mixture of H2, I2, and HI at 500 K, [HI] = 2.21 x 10^-3 mol/L and [I2] = 1.46 x 10^-3 mol/L. Given the value of the equilibrium constant in table 5G.2, calculate the equilibrium molar concentration of H2." How do you know what the products and reactants are betw...

Alyssa Bryan 3F

Equilibrium constants (Kp) will not have units for your final answer, so while you are evaluating with partial pressure the units do not matter as long as all the partial pressures have the same units.

Alyssa Bryan 3F

In high school, I was taught to add a sig fig when you take the -log to calculate the pH; however, there have been different things said about sig figs for this class regarding this topic. What is the expected rule for sig figs when taking the log that I should follow?

Alyssa Bryan 3F

What specific coordination compounds are necessary to know their biological importance?

Alyssa Bryan 3F

Do we have to memorize all the common ligands in the table on pg. 724?

Alyssa Bryan 3F

I know that lewis acids accept electrons while lewis bases donate electrons, but how can you determine whether the species is able to accept or donate the electron pairs? Do you have to draw the lewis structures to determine this?

Alyssa Bryan 3F

What is a chelating complex and how can you determine whether or not one will form between the three isomers of diaminobenzene given?

Alyssa Bryan 3F

For part a of the question the name of [Fe(CN)6]4- is hexacyanoferrate(ii) ion. Why is "ferrate" used for the naming of Fe when the element is iron?

Alyssa Bryan 3F

State the relative orientation of each of the following hybrid orbitals: (a) sp3; (b) sp; (c) sp3d2; (d) sp2
How do you determine the orientation of these hybrid orbitals?

Alyssa Bryan 3F

Is there another way to determine the hybridization of an atom without drawing the molecule's lewis structure or is that the only way to determine hybridization?

Alyssa Bryan 3F

Besides that a single bond = 1 sigma bond, a double bond = 1 sigma + 1 pi bond, and a triple bond = 1 sigma + 2 pi bonds, what else is important about these types of bonds? What is the concept behind them?

Alyssa Bryan 3F

For part d of the question where it asks for the Lewis structure and bond angle N2H4, the book gives the exact bond angle of 107. I know in class Dr. Lavelle said for trigonal pyramidal structures we only have to know that the angle is less than 109.5, so for our answer would it be okay to say less ...

Alyssa Bryan 3F

For part (a) I3- the lewis structure in the book is vertical. Is it important to draw the linear structure vertically rather than horizontally?

Alyssa Bryan 3F

What molecular shapes do we need to know the exact bond angles of and what molecular shapes do we need know that are less than 120 or 109.5 and not the exact angles?

Alyssa Bryan 3F

For the CH2F2 structure, the answer in the book shows more of a 3D model indicated by the filled in wedge and striped line wedge for the bonds between the carbon and hydrogens. Do we need to draw the lewis structure like that or can we draw it how we have been doing, in the 2D model?

Alyssa Bryan 3F

Which of these compounds has bonds that are primarily ionic? (a) BBr3; (b) BaBr2; (c) BeBr2
Why is BeBr2 not considered to have primarily ionic bonds as the compound is between a metal and nonmetal, meaning it has ionic bonds?

Alyssa Bryan 3F

Place the following molecules or ions in order of decreasing bond length: the CO bond in CO, CO2, CO3^2-... How do you determine the bond lengths for these molecules/ions in order to determine the order? Do you need to draw the lewis structures?

Alyssa Bryan 3F

For these compounds, ammonium chloride, potassium phosphide, and sodium hypochlorite, why do you separate them into their cations and anions to draw the Lewis structures?

Alyssa Bryan 3F

In the given lewis structure, how are you able to identify the unknown element?

Alyssa Bryan 3F

If there were no lone pairs on Br and you fulfilled the octet rule for F then you would not have used all valence electrons. For BrF3 there are 28 valence electrons, meaning two lone pairs need to be placed on Br as just fulfilling the octet rule for the the fluorines uses 24 electrons.

Alyssa Bryan 3F

I am a little confused how to predict the ions for these two problems. 2A.9 Which M^2+ ions (M=metal) are predicted to have the following ground-state electron configurations: (a) [Ar]3d7 (b) [Ar]3d6 2A.11 Which M^3+ ions (M=metal) are predicted to have the following ground-state electron configurat...

Alyssa Bryan 3F

Degeneracy refers to when an orbital has equal energy. For example, the p orbital would have a degeneracy of 3 and the d orbital a degeneracy of 5.

Alyssa Bryan 3F

I am also confused on how sulfur was the answer for 11c. I was also wondering how to know that the electron affinity for (b) beryllium and magnesium and (d) gallium and indium are equal.

Alyssa Bryan 3F

The uncertainty in position would be 350. pm, but in order to apply it to the equation you need to convert this to meters so the units will align with one another.

Alyssa Bryan 3F

Can someone explain the reason the 2d and 4g subshells cannot exist in an atom?

Alyssa Bryan 3F

I think for this question the answer in the back of the book is wrong. On the chemistry 14A webpage in the solution manual errors page it shows this problem is one of them. So instead of the answer being 1.3 x 10^-36 it is actually 6.7 x 10^-37. This is because the Δv should be 10, not 5 in the equa...

Alyssa Bryan 3F

Will we also have to know the Paschen series (lower energy level is n=3) and the Brackett series (lower energy level is n=4) for assignments/tests if so far in class we have only discussed the Lyman series and Balmer series?

Alyssa Bryan 3F

In part B of this question, it asks for how much energy is emitted by 5.00 mg of sodium atoms and in part c is asks for how much energy is emitted by 1.00 mol of sodium atoms, both emitting light at a wavelength of 589 nm. How are you able to go from grams and mols of sodium atoms to joules?

Alyssa Bryan 3F

In this question, the energy is given in keV and we are given a conversion from eV to joules. What is keV and what is the difference between this unit of measurement and joules?

Alyssa Bryan 3F

"Sodium bromide, NaBr, which is used to produce AgBr for use in photographic film, can itself be prepared as follows: Fe + Br2 --> FeBr2 FeBr2 + Br2 --> Fe3Br8 FeBr2 + Na2CO3 --> NaBr + CO2 + Fe3O4 What mass of iron, in kilograms, is needed to produce 2.50 t of NaBr? Note that these equations m...

Alyssa Bryan 3F

Is it possible to determine the limiting reactant a different way than how it was taught in class? I think in high school I was taught to convert the moles of each reactant to moles of product and then compare the product moles instead of just comparing the moles of the reactants to determine the li...

Alyssa Bryan 3F

First you need to figure out what the metal (M) is in the metal hydroxide M(OH)2. Since you have the molar mass of the metal hydroxide you can subtract the molar mass of (OH)2 to find the molar mass of the metal. 74.10-34.02=40.08 g/mol 40.08 is the molar mass of calcium (Ca) so the sulfide would ju...

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