CHEMISTRY COMMUNITY

Lina Petrossian 1D

This part of the test asked to write the 2 species from parts a and b that would give the largest E cell if assembled in an electrochemical cell. How do we do this in general?

Lina Petrossian 1D

How can we determine in a multistep reaction, which compounds are the intermediates and which is the catalyst?

Lina Petrossian 1D

15.65 For the reversible, one-step reaction 2 A <--> B + C, the forward rate constant for the formation of B is 265 L mol-1 min-1 and the rate constant for the reverse reaction is 392 L mol-1 min-1. The activation energy for the forward reaction is 39.7 kJ mol-1 and that of the reverse reaction is 2...

Lina Petrossian 1D

Step 1 produces Cl and Step 2 uses Cl- as a reactant. How come the solutions manual states that the chloride ion is an intermediate. Is it just a typo that Cl doesnt have the negative symbol in step 1?

Lina Petrossian 1D

15.39 Determine the time required for each of the following second-order reactions to take place: (a) 2 A -> B + C, for the concentration of A to decrease from 0.10 mol L-1 to 0.080 mol L-1, given that k = 0.015 L mol-1 min-1 for the rate law expressed in terms of the loss of A; (b) A -> 2 B + C, wh...

Lina Petrossian 1D

Will there be a difference in my answer if I calculate Gibbs free energy using the formula for products minus reactants or if I use the formula including enthalpy?

Lina Petrossian 1D

How do we know when to use the different formulas for gibbs free energy?

Lina Petrossian 1D

Can someone explain the order that we list the molecules in the cell diagram?

Lina Petrossian 1D

14.91 A voltaic cell functions only when the electrical circuit
is complete. In the external circuit the current is carried by the flow of electrons through a metal wire. Explain how the current is carried through the cell itself.

Could someone give a detailed explanation?

Lina Petrossian 1D

14.101 In a neuron (a nerve cell), the concentration of K+ ions inside the cell is about 20–30 times as great as that outside. What potential difference between the inside and the outside of the cell would you expect to measure if the difference is due only to the imbalance of potassium ions? Could ...

Lina Petrossian 1D

How do we know when to include Platinum in a cell diagram. On the left, right, or both or not at all?

Lina Petrossian 1D

How come in the example reaction on this page it states that the hydrogen electrode is the cathode, when Zn2+ is reduced??

Lina Petrossian 1D

So if the answer is -196.10 kj/mol. What is per mol referring to? Per mole of what? Why is the answer not half that value like i originally got?

Lina Petrossian 1D

Hi unfortunately I am still confused. The answer -196.10 kj per mole is actually per 2 moles of H2O2 decomposed. Therefore, shouldnt the answer be half of that in order to get per mole decomposed??

Lina Petrossian 1D

9.57 Calculate the standard reaction entropy, enthalpy, and Gibbs free energy for each of the following reactions from data in Appendix 2A: (a) the decomposition of hydrogen peroxide: 2 H2O2(l) -> 2 H2O(l) + O2(g) Why is the answer for delta H in the textbook kj per mole when the reaction is not dec...

Lina Petrossian 1D

9.57 Calculate the standard reaction entropy, enthalpy, and Gibbs free energy for each of the following reactions from data in Appendix 2A: (a) the decomposition of hydrogen peroxide: 2 H2O2(l) -> 2 H2O(l) + O2(g) For part a, I keep getting delta H = -98.05 kj per mole, but thats not what it says in...

Lina Petrossian 1D

Under what circumstances does delta(S)tot = delta(S)sys + delta(S)surr = 0. And under what circumstances does delta(U) = q + w = 0.

Lina Petrossian 1D

On the midterm would we be expected to use formulas such as C= 4R?

Lina Petrossian 1D

How would the problem be solved if it had asked for delta(H) of system instead of surroundings?

Lina Petrossian 1D

8.67 Use the information in Tables 8.3, 8.6, and 8.7 to estimate the enthalpy of formation of each of the following compounds in the liquid state. The standard enthalpy of sublimation of carbon is 717 kJ·mol-1. (a) H2O; (b) methanol, CH3OH; (c) benzene, C6H6 (without resonance); (d) benzene, C6H6 (w...

Lina Petrossian 1D

8.41 A 50.0-g ice cube at 0.0 C is added to a glass containing 400.0 g of water at 45.0 C. What is the final temperature of the system (see Tables 8.2 and 8.3)? Assume that no heat is lost to the surroundings. Is this the correct setup? (500)(4.184)(T-45)= -16694.44 - (50)(4.184)(T) Because I keep g...

Lina Petrossian 1D

8.21 A piece of copper of mass 20.0 g at 100.0 C is placed in a vessel of negligible heat capacity but containing 50.7 g of water at 22.0 C. Calculate the final temperature of the water. Assume that no energy is lost to the surroundings. Why do we use this setup: 20 (mass)*0.39 (specific heat of Cu)...

Lina Petrossian 1D

How come example 8.3 uses 80 K in the calculations? When the question is stated in degrees C?

Lina Petrossian 1D

Could someone explain why a cup of tea is considered an open system?

Lina Petrossian 1D

Could someone list examples for each of these systems?

Lina Petrossian 1D

Could someone explain why a water bottle (for example those that keep drinks warm) are considered isolated?

Lina Petrossian 1D

12.57 (a) When the pH of 0.10 m HClO2(aq) was measured, it was found to be 1.2. What are the values of Ka and pKa of chlorous acid? (b) The pH of a 0.10 m propylamine, C3H7NH2, aqueous solution was measured as 11.86. What are the values of Kb and pKb of propylamine? Can someone explain step by step ...

Lina Petrossian 1D

• Identify reactions where the ideal gas law can be used as an approximation.

Can someone explain this please?

Lina Petrossian 1D

"Use Le Chatelier's principle to predict how the equilibrium composition of a reaction mixture is
affected by: adding or removing reagents; compressing or expanding a gaseous mixture; and
by raising or lowering the temperature."

Can someone pls give a summary of this?

Lina Petrossian 1D

11.79 A reactor for the production of ammonia by the Haber process is found to be at equilibrium with PN2 = 3.11 bar, PH2 = 1.64 bar, and PNH3 = 23.72 bar. If the partial pressure of N2 is increased by 1.57 bar, what will be the partial pressure of each gas once equilibrium is re-established? How do...

Lina Petrossian 1D

11.77 Predict whether each of the following equilibria will shift toward products or reactants with a temperature increase: (a) N2O4(g) <-> 2 NO2(g), H = +57 kJ (b) X2(g) <-> 2 X(g), where X is a halogen (c) Ni(s) + 4 CO(g) <-> Ni(CO)4(g), H = -161 kJ (d) CO2(g) + 2 NH3(g) <-> CO(NH2)2(s) + H2O(g), ...

Lina Petrossian 1D

11.57 A reaction mixture consisting of 2.00 mol CO and 3.00 mol H2 is placed in a 10.0-L reaction vessel and heated to 1200. K. At equilibrium, 0.478 mol CH4 was present in the system. Determine the value of Kc for the reaction CO(g) + 3 H2(g) <--> CH4(g) + H2O(g) at 1200. K. Is anyone else getting ...

Lina Petrossian 1D

11.45 (a) A sample of 2.0 mmol Cl2(g) was sealed into a 2.0-L reaction vessel and heated to 1000. K to study its dissociation into Cl atoms. Use the information in Table 11.2 to calculate the equilibrium composition of the mixture. (b) If 2.0 mmol F2 was placed into the reaction vessel instead of th...

Lina Petrossian 1D

11.41 A 25.0-g sample of ammonium carbamate, NH4(NH2CO2), was placed in an evacuated 0.250-L flask and kept at 25 C. At equilibrium, 17.4 mg of CO2 was present. What is the value of Kc for the decomposition of ammonium carbamate into ammonia and carbon dioxide? The reaction is NH4(NH2CO2)(s) -> 2 NH...

Lina Petrossian 1D

11.33 A 0.500-L reaction vessel at 700. K contains 1.20 mmol SO2(g), 0.50 mmol O2(g), and 0.10 mmol SO3(g). At 700. K, Kc = 1.7 x 10^6 for the equilibrium 2 SO2(g) + O2(g) -> 2 SO3(g). (a) Calculate the reaction quotient Qc. (b) Will more SO3(g) tend to form? Why does part b answer state that Q > K?

Lina Petrossian 1D

Can someone please explain why and when we can use pressure or concentration to calculate the constant K?

Lina Petrossian 1D

11.9 Balance the following equations using the smallest whole- number coefficients, then write the equilibrium expression Kc for each reaction: (a) CH4(g) + O2(g) -> CO2(g) + H2O(g) (b) I2(g) + F2(g) -> IF5(g) (c) NO2(g) + F2(g) -> FNO2(g) For Kc do we simply write the expression without any actual ...

Lina Petrossian 1D

11.1 State whether the following statements are true or false. If false, explain why. (a) A reaction stops when equilibrium is reached. (b) An equilibrium reaction is not affected by increasing the concentrations of products. (c) If one starts with a higher pressure of reactant, the equilibrium cons...

Lina Petrossian 1D

How can we tell if a shape is tetrahedral or square planar?

Lina Petrossian 1D

ThomascnguyenDis1J wrote:When dealing with multiple compounds bonding to each other, what is the best way to determine its molecular shape?

I would say look at it one atom at a time. I believe we are not responsible for figuring out the shapes of molecules with many bonds.

Lina Petrossian 1D

I think I understand the basis of how to do number 34, but I keep getting a pH of 2.10. Did anyone else make the error same/know what my error is? I'm getting that same answer :( The 1st step is to write out the acid and base equation, [HCl] + [H2O] =>[H3O^+] + [OH^-] and [CaO] + [H2O] => [Ca^+] + ...

Lina Petrossian 1D

How are we supposed to know the biological impacts of compounds like these?

Lina Petrossian 1D

Is the name of the cation that is outside of the brackets a part of the naming word? Or does the naming of the compound become two words?

Lina Petrossian 1D

Will we be learning more about weak acids in 14B or not at all?

Lina Petrossian 1D

Could someone please explain the definition of a conjugate base?

Lina Petrossian 1D

bonnie_schmitz_3K wrote:I think I understand the basis of how to do number 34, but I keep getting a pH of 2.10. Did anyone else make the error same/know what my error is?

I'm getting that same answer :(

Lina Petrossian 1D

When will answers be posted?

Lina Petrossian 1D

Meachelle_Lum_3C wrote:For 33c, since we have a weak base, we will have less OH since it doesn’t completely dissociate. However, since less OH means more H3O, this means less pOH should mean more pH. Why did Lyndon say lower pH instead?

More H30 means more proton concentration, meaning a lower (more acidic) pH value.

Lina Petrossian 1D

Thank you! Got it!

Lina Petrossian 1D

In the quantum world, we have learned a lot of equations. Can someone give an explanation for when and what types of problems we would use each equation?

Lina Petrossian 1D

17.31 Use the information in Table 17.4 to write the formula for each of the following coordination compounds: (a) potassium hexacyanidochromate(III) (b) pentaamminesulfatocobalt(III) chloride (c) tetraamminediaquacobalt(III) bromide (d) sodium bisoxalato(diaqua)ferrate(III) Part d: Why is (OH2)2 wr...

Lina Petrossian 1D

3.71 Select from each of the following pairs of Lewis structures the one that is likely to make the dominant contribution to a resonance hybrid. Explain your selection.

How do we know which one to select?

Lina Petrossian 1D

4.21 Write the Lewis structure and give the approximate bond angles of (a) C2H4; (b) ClCN; (c) OPCl3; (d) N2H4.

Could someone explain how to approximate the bond angles and why part a is trigonal planar?

Lina Petrossian 1D

4.19 Predict the shapes and estimate the bond angles of (a) the thiosulfate ion, S2O32-; (b) (CH3)2Be; (c) BH2-; (d) SnCl2.

Could someone explain how they determined the bond angles as well as explain why part b is linear?

Lina Petrossian 1D

4.13 Write the Lewis structure, VSEPR formula, molecular shape, and bond angles for each of the following species: (a) I3-; (b) POCl3; (c) IO3-; (d) N2O.

Could someone explain how we are supposed to know what the bond angles are?

Lina Petrossian 1D

4.7 (a) What is the shape of the thionyl chloride molecule, SOCl2? Sulfur is the central atom. (b) How many different OSCl bond angles are there in this molecule? (c) What values are expected for the OSCl and ClSCl bond angles?

How did you guys attempt this problem?

Lina Petrossian 1D

4.3 Draw the structures and name the shapes of the following molecules: (a) HCN; (b) CH2F2.

Can someone explain how they drew these?

Lina Petrossian 1D

4.1 Below are ball-and-stick models of two molecules. In each case, indicate whether there must be, may be, or cannot be one or more lone pairs of electrons on the central atom.

Could someone explain how they solved this?

Lina Petrossian 1D

3.39 Write the complete Lewis structure for each of the following compounds: (a) ammonium chloride; (b) potassium phosphide; (c) sodium hypochlorite.

For part b, how do we format the lewis structure? Can we write 3K+ or do we have to write 3 separate K+'s?

Lina Petrossian 1D

3.37 The following Lewis structure was drawn for a Period 3 element. Identify the element.

I got phosphorus, did anyone else get this as an answer?

Lina Petrossian 1D

3.53 Determine the formal charge on each atom in the following molecules. Identify the structure of lower energy in each pair.

Could someone explain how they solved this problem?

Lina Petrossian 1D

How do you go about solving the first problem?

Lina Petrossian 1D

Keshav Bhatnagar wrote:If you check the solutions manual, [Ar]3d^8 is the correct answer.

Thank you for clarifying. Unfortunately, I do not have access to the solutions manual.

Lina Petrossian 1D

3.19 Give the ground-state electron configuration and number of unpaired electrons expected for each of the following ions: (a) Sb3+; (b) Sn4+; (d) Br-; (e) Ni2+.

For part e my answer is [Ar]3d8 with 2 unpaired electrons. Did others get different answers?

Lina Petrossian 1D

For a) [Ar] b)[Kr]4d105s2 c)[Xe] d)[Kr]4d10. For all of them i got 0 unpaired electrons. Is this what you got?

Lina Petrossian 1D

As an example of 3d this is another way of writing (n)(l) since n = 3 and l = 2 = d for all angular momentum quantum numbers we have l=0; s l=1; p l=2; d l=3; f l=4; g for the first question (a) 6p; (b) 3d; (c) 2p; (d) 5f (a) n =6 and l = 1 (b) n = 3 and l = 2 (c) n = 2 and l = 1 (d) n = 5 and l = ...

Lina Petrossian 1D

1.37 Protons and neutrons have nearly the same mass. How different are their wavelengths? Calculate the wavelength of each particle when traveling at 2.75 x 10^5 m x s^-1 in a particle accelerator and report the difference as a percentage of the wavelength of the neutron. What does it mean by "...

Lina Petrossian 1D

The velocity of an electron that is emitted from a metallic surface by a photon is 3.6x10^3 km.s-1. (a) What is the wavelength of the ejected electron? (b) No electrons are emitted from the surface of the metal until the frequency of the radiation reaches 2.50x10^16 Hz. How much energy is required t...

Lina Petrossian 1D

Thanks!

Lina Petrossian 1D

A college student recently had a busy day. Each of the student’s activities on that day (reading, getting a dental x-ray, making popcorn in a microwave oven, and acquiring a suntan) involved radiation from a different part of the electromagnetic spectrum. Complete the following table and match each ...

Lina Petrossian 1D

Arlene Linares 3A wrote:
Justin Le 2I wrote:I think we will because you can't get make up extra significant figures. We have to get our answer from what data is available to us.

If we get it wrong do you think we will still get partial credit for trying?

I think we will as long as our answer is relatively close to the actual answer.

Lina Petrossian 1D

When taking values from the periodic table (ex. for calculating molar mass), how many significant figures do you round to? Try to not round answers until the very last step. I usually use the entire given value from the periodic table then round to the smallest number of significant figures used in...

Lina Petrossian 1D

I usually use the second method of "calculating both reactants in terms of moles and balancing them and then seeing which one is less" for the same reasons mentioned above. If the question has multiple parts following, then it usually gives you a head start on the other parts. But it only ...

Lina Petrossian 1D

I believe the combined molar mass of CuSO4 and 5H2O is 249.68 g/mol. Which when multiplied by 0.05 mol gives 12.484 g CuSO4 5H2O.

Lina Petrossian 1D

For problem G5, I got the following answers: a. 0.013 L, b. 0.06225 L, and c. 0.0059 L. Did anyone else get these answers?

Lina Petrossian 1D

Thank you!

Lina Petrossian 1D

E17: Which sample in each of the following pairs contains the greater number of moles of atoms? (a) 75 g of indium or 80 g of tellurium; (b) 15.0 g of P or 15.0 g of S; (c) 7.36 x 10^27 atoms of Ru or 7.36 x 10^27 atoms of Fe. I believe I know how to solve a and b, but for c my answer is that they c...

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