CHEMISTRY COMMUNITY

Shannon Wasley 2J

Would it be safe to say that the difference between a catalyst and an intermediate is that an intermediate is produced in one step and consumed in the following step and a catalyst is used in one step and can be a product of a following step?

Shannon Wasley 2J

In the solutions's manual, the A's seem to be cancelled out. Why can we do this, when the question says that they are different values?

Shannon Wasley 2J

For some of the homework problems in Chapter 15, the problem asked to find the time it would take for the concentration to get to 1/4 or 1/8 of its original value. For a first order reaction, I worked it out that if the half life was, for example, 100 seconds and this was the value for the initial c...

Shannon Wasley 2J

Is the Transition State Theory just a more broad concept than the Collision theory?

Shannon Wasley 2J

For some of the problems in Chapter 14, we have notice that when comparing two cell potentials from Appendix 2A, the lower or more negative cell potential means that half-reaction is an anode and therefore the more positive one is the cathode. However, in other questions when using Appendix 2A, some...

Shannon Wasley 2J

For this type of problem, is it recommended to not multiply by F and then at the end just cancel out the F's. Or will we get the same answer if we multiply and divided by F?

Shannon Wasley 2J

When a question asks "how much time will elapse in a first order reaction for the concentration of A to decrease to 1/8[A] (not), I plug in ln(1/8) = -kt + (ln(1)) and I seem to get the right answer every time. However, if it were a second-order reaction and I tried using the same method, for e...

Shannon Wasley 2J

Can someone explain why the units of k for zero, first, and second order reactions are mol/L sec, s^-1, and L/mol sec, respectively?

Shannon Wasley 2J

When using this formula, what values of R and T would we use?

Shannon Wasley 2J

Mercury is a toxic heavy metal pollutant whose concentration in aqueous solution depends in part on the redox properties of compounds containing mercury. Suppose you are studying the properties of mercury. You might need to construct an electro- chemical cell; you then would need to write down the c...

Shannon Wasley 2J

In cell diagrams, how do we order the compounds or molecules on one of the sides of the salt bridge. For example, for the anode, are we supposed to order the electrodes in a specific order? Like by alphabetical order of states or by reactants then products? I'm not sure this question made any sense.

Shannon Wasley 2J

What would be an example of a reaction that does not need a salt bridge and therefore we would not put double lines in the cell diagram?

Shannon Wasley 2J

This is a question about Self-Test 14.3A: The reaction taking place in a nicad (nickel–cadmium) cell is Cd(s) + 2 Ni(OH)3(s) --> Cd(OH)2(s) + 2 Ni(OH)2(s), and the cell potential when fully charged is 1.25 V. What is the reaction Gibbs free energy? I understand that we are supposed to use the formul...

Shannon Wasley 2J

The problem is: Beta blockers are drugs that are used to manage hypertension. It is important for doctors to know how rapidly a beta blocker is eliminated from the body. A certain beta blocker is eliminated in a rst-order process with a rate constant of 7.6 10 3 min 1 at normal body temperature (37 ...

Shannon Wasley 2J

For this problem, I am getting the right numbers however they are off by several powers of 10. For part c, why is the value of k = 2.85 x10^12? I found that k was equal to 2.85 when dividing 8.7 by (1.25^5). Then when I tried finding the initial rate from the given concentrations, I got a number tha...

Shannon Wasley 2J

What are the orders of the reactants for this question?

Shannon Wasley 2J

In the cell diagram for this part, why is there a KOH instead of simply OH?

Shannon Wasley 2J

Why are the half reactions Au+(aq) + e- --> Au(s) and Au(s) --> Au3++ 3e-?

Shannon Wasley 2J

Are the double lines between the anode and cathode always used, or is there any situation where the cell diagram would not have the double lines?

Shannon Wasley 2J

How did the solutions manual get the anode and cathode reactions that they got for part c of 14.13? How do we know to separate HCl?

Shannon Wasley 2J

Does the metal always have to be a solid to be used as an electrode?

Shannon Wasley 2J

When balancing the redox reaction, we have to balance the oxygens by adding H2O, but then it causes there to be a difference of hydrogens on the reactant side versus product side. When balancing these hydrogens, should we use H3O + or H+?

Shannon Wasley 2J

Yes, for a bomb calorimeter problem, the equation for q is q=CdeltaT

Shannon Wasley 2J

At constant volume, w = 0, therefore, the equation delta U = q +w would be delta U = q. However, q would only be equal to delta H if the reaction was also at constant pressure.

Shannon Wasley 2J

Delta H is not necessarily equal to 0 at constant pressure. At constant pressure delta H is equal to q. Therefore if q were equal to 0 at constant pressure, then delta H would also be 0

Shannon Wasley 2J

If in an isothermal process there is no change in temperature, why wouldn't the value of q be 0, since the equation is q = mCdeltaT. Why isn't this delta T equal to 0 due to the fact that the process is isothermal?

Shannon Wasley 2J

yes. Thus making w = -q

Shannon Wasley 2J

In the "Errors in the solution manual", when finding the entropy due to the change in temperature, Cv is used and has a value of 5/2R. I understand why it would be 5/2R instead of 3/2R since it is a diatomic molecule. However, I do not understand why Cv was used, since there was a change i...

Shannon Wasley 2J

Hydrochloric acid oxidizes zinc metal in a reaction that produces hydrogen gas and chloride ions. A piece of zinc metal of mass 8.5 g is dropped into an apparatus containing 800.0 mL of 0.500 m HCl(aq). If the initial temperature of the hydrochloric acid solution is 25 C, what is the nal temperature...

Shannon Wasley 2J

The oxidation of nitrogen in the hot exhaust of jet engines and automobile engines occurs by the reaction N2 (g) + O2 (g) 2 NO (g) ΔHo = +180.6 kJ Part C: When the oxidation of N2 to NO was completed in a bomb calorimeter, the heat absorbed was measured as 492 J. What mass of nitrogen gas was oxidiz...

Shannon Wasley 2J

Is it correct to say that the units of delta H are only in kJ or J and that the units of delta H naught are only in kJ/mol or J/mol?

Shannon Wasley 2J

When using bond enthalpies to solve for the enthalpy of formation, does it only give us the value of the compound in its gas form?

Shannon Wasley 2J

Question 8.67 asked us to use tables 3, 6, and 7. For part A, we have to find the enthalpy of formation of H20, and we do this using bond enthalpies which are found in tables 6 and 7. However, this only gives us the enthalpy of water in the gas form. Therefore we have to use the formula ∆Hvap = H(va...

Shannon Wasley 2J

In the solution's manual, they show the reaction that we are trying to get which is N2 + 5/2 O2 --> N2O5. Then they add the two given equations together and solve for the enthalpy of this new reaction. Then they set the enthalpy of this reaction set equal to the enthalpy of formation of N2O5 minus t...

Shannon Wasley 2J

An extensive property is dependent on the amount of matter present, while an intensive property does not depend on this amount. An extensive property would be heat capacity, for example. This is because the larger the amount of the substance, the more heat that is required to raise its temperature.

Shannon Wasley 2J

just free energy

Shannon Wasley 2J

The key word here is formation. The formation of bonds requires energy. When finding enthalpies of formation for an entire reaction using the change in enthalpy at standard state of molecules, you can rely on enthalpy's status as a state function and subtract the change in enthalpy of the reactants ...

Shannon Wasley 2J

The balanced equation would be CO(g) + H2O(g) →CO2(g) + H2(g). Water vapor is water but in gas form. Hydrogen gas is H2.

Shannon Wasley 2J

The molar heat capacity for a monatomic gas at constant volume, C (v,m) is 3/2R. Therefore when we use the equation q = nC(m)deltaT, we get q = n 3/2RdeltaT, when we plug in our molar heat capacity for a monatomic gas. Since this molar heat capacity is at constant volume, delta V = 0 and therefore w...

Shannon Wasley 2J

Why when calculating the heat of the ice cube do we use the specific heat capacity of water (4.184)? Why wouldn't we use the specific heat capacity of ice (2.108)?

Shannon Wasley 2J

The first step in finding the change in enthalpy of combustion reactions is creating each combustion reaction and balancing each equation. The problem gives you the compounds in which you have to make a combustion reaction for. For each compound you add 02 as a reactant and the products would be CO2...

Shannon Wasley 2J

How do we determine whether the sign on q is positive or negative, if we are only given the number and not the sign? For example, if it said that it required 5.5 kJ of heat. How would we know if that value was positive or negative?

Shannon Wasley 2J

This relates to the concept of rotational kinetic energy. The more complex a molecule, such as being composed of molecules versus being monatomic, the greater the molar heat capacity due to rotational kinetic energy and translational kinetic energy.

Shannon Wasley 2J

It would also be the same as using the differing values of R, depending on the units. 8.314 J·K-1·mol-1 = 8.206 x 10-2 L·atm·K-1·mol-1. Therefore you could multiply your answer that is in L·atm by (8.314 J·K-1·mol-1/8.206 x 10-2 L·atm·K-1·mol-1)

Shannon Wasley 2J

Will there be reversible processes on Test 1?

Shannon Wasley 2J

In regards to heat capacity, is it safe to assume that when we are finding the heat capacity at constant volume, we use U and when we are finding the heat capacity at constant pressure, we use H? Also, ignoring heat capacity, when we are simply finding delta H, is it always at a constant pressure, o...

Shannon Wasley 2J

What is the difference between an isolated and closed systems in relevance to question 8.1?

Shannon Wasley 2J

For part b, the first step would be to use the formula: M(initial)V(initial) = M(final)V(Final) The initial M is given: .025 The initial volume is given: 200mL --> .200L The final volume is also given: 250mL --> .250 Therefore by solving (.200)(.025) = (.250)x, you get the final concentration is equ...

Shannon Wasley 2J

What would the Lewis Structure of [HgF2(OH2)2]+ look like, since Hg is part of the d elements?

Shannon Wasley 2J

Conjugate bases is the compound remaining after an acid has donated a proton (H+). Therefore in reference to this problem, the conjugate base would be drawn by removing the one H atom, which is the H+ proton that the acid donates. The conjugate base of the given acid would just be without the Hydrog...

Shannon Wasley 2J

Yes that is correct. The value of K is found by dividing the concentrations of the products by the concentrations of the reactants. Therefore, K would be small if there was a much higher value for the concentration of reactants than for the products, therefore there are more reactants than products

Shannon Wasley 2J

Do Bronsted Bases always have a lone pair? Is this the defining characteristic to determine that the base is Bronsted?

Shannon Wasley 2J

Cubic equations form due to "x" being in the change part of the ICE table. In terms of simplifying the cubic equation, when K < 10^-3, it is taken out of the cubic equation, since it is nearing 0 and will get answers that are different than the actual answer.

Shannon Wasley 2J

The concentration would be in reference to the specific molar concentration of the compound whose partial pressure is being used in the equation.

Shannon Wasley 2J

The first step is to find the moles of PCl5 from the given amount of PCl5 in grams, which is 1.0g. You would divide the 1.0g by the molar mass of PCl5 to get the amount of moles, which came out to be .019 moles of PCl5 For the I portion of the table: PCl5: .019, PCl3: 0, Cl2: 0 For the C portion of ...

Shannon Wasley 2J

The equation used for this problem would be K = (Pn2)(Po2)/(Pno)^2. The equilibrium relation is equal to the Pressures of the reactants divided by the products, but for this the produce NO has a stoichiometric coefficient of 2, which is why it is squared.

Shannon Wasley 2J

Test 4 covers material up to HW 11.63

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Each carbon in C2H2 is sp^2 hybridized. There are two carbons in the equation, which means the hybridization is 2sp^2

Shannon Wasley 2J

Trans isomers tend to be non polar or less polar than cis isomers, which tend to be polar, which is a characteristic of their higher boiling points and lower melting points

Shannon Wasley 2J

In the book, it says that an electron is promoted in carbon, in order for carbon to have four valence electrons. Why do we write the electron configuration as [He] 2s^2 2p^2, when for most carbons in a molecule, we promote an electron so it is [He] 2s^1 2p^3? In other words why don't we just write t...

Shannon Wasley 2J

More electronegative elements have higher tendencies to pull electrons towards themselves. Therefore, the higher electronegative an electron the more likely the will want to obtain a full octet. For example, in the case of nitrogen monoxide (NO), there are 11 valence electrons that need tone placed ...

Shannon Wasley 2J

Based on the periodic table, chlorine has seven valence electrons and oxygen has 6 electrons which is equal to 13 valence electrons, illustrating a violation of the octet rule, since it is an odd number of valence electrons. Therefore, chlorine would be without an 8th valence electrons, since there ...

Shannon Wasley 2J

In relation to increasing electron affinity across a row, how would the electron affinities of the halogens compare to the electron affinities of the noble gases, if they are in the same row. For example, how would Chlorine and Argon relate in terms of electron affinity?

Shannon Wasley 2J

My TA had said that they do continue down the columns, however we would not be asked specific questions about the electron configurations of those elements on the tests. We would only need to know that chromium and copper are exceptions to the electron configuration rule

Shannon Wasley 2J

First, we can look at the electron configuration of Fe which is [Ar] 4s^2 3d^6, but we put it in the form [Ar] 3d^6 4s^2, based on 3 being at a lower energy level than 4. Fe 2+ needs to donate two valence electrons and these come from the highest energy level which would be 4s. For chromium it is mo...

Shannon Wasley 2J

For most problems it is preferred that the value of the wavelength is in nanometers because it is then easier to see where along the electromagnetic spectrum the wavelength falls. Also, it could be useful to have the value in nanometers for when the next part of the questions asks for what type of r...

Shannon Wasley 2J

There are also times where it would be faster to use the formula that the book had given us, which would be why they included it in the first place. However, the formula from the lecture better illustrates what is occurring as the change from one level to another occurs. If a question asked specific...

Shannon Wasley 2J

I know that we need to know some of the conversions and constants, but would we have to know that 1 eV is equal to 1.6022 x 10^-19 J for the test. Or would we just need to know how to use the number in the problem to get our answer and not memorize it.

Shannon Wasley 2J

For future tests about the Quantum World and the Properties of Light, will we need to know the range of wavelengths of visible light (400 - 700nm). Also, will we need to know what color is seen at which wavelength. For example, will a test problem have us solve for the wavelength and then have us de...

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Step 1: Since we know are calculating for formula units, we want to convert our grams of the compound to moles so we can use Avogadro's number which is 6.022 x 10^23 formula units/ mol 5.15g MgSO4 7H20 x 1 mol MgSO4 7H2O/ 246.48gMgSO4 7H2O (this is the molar mass of the compound). The grams would ca...

Shannon Wasley 2J

The question is: Epsom salts consist of magnesium sulfate heptahydrate. Write its formula. (a) How many atoms of oxygen are in 5.15 g of Epsom salts? (b) How many formula units of the compound are present in 5.15g? (c) How many moles of water molecules are in 5.15 g of Epsom salts? For part a, I und...

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