CHEMISTRY COMMUNITY

Hannah_1G

You would take the half reactions: 2H+ (aq,1.0M) + 2e- --> H2 (g,1atm) // E cathode = 0.00V H2 (g,1atm) --> 2H+ (aq,0.075M) + 2e- // E anode = 0.00V Add them together: 2H+ (aq, 1.0M) + H2 (g,1atm) --> 2H+ (aq,0.075M) + H2 (g,1atm) and get Ecell = 0.00V Then use the nernst equation to get: E=E^\circ...

Hannah_1G

How does this cell diagram work Pt(s)|H 2 (g, 1.0 bar)|HCl(aq, 0.075 mol/L )||HCl(aq, 1.0 mol/L)|H 2 (g, 1.0 bar)|Pt(s)
and how would I balance it to solve for its cell potential?

Hannah_1G

Similarly with $Cu(s)|Cu^{2+}(aq)||Ce^{4+}(aq),Ce^{3+}(aq)|Pt(s)$ , how do I view the commas in the diagram to write out a half redox reaction?

Hannah_1G

In the cell diagram:
$C(gr)|H_{2}(g)|H^{+}(aq)||Cl^{-}(aq)|Cl_{2}(g)|Pt(s)$
H and Cl look like they are both oxidized, how would I write the half redox reactions?

Hannah_1G

How would you go about finding k in part c? 2A $\rightarrow$ B + C, given that [A]0 = 0.153 mol/L and that after 115 s the concentration of B rises to 0.034 mol/L. Would I use 1/2 A= change in concentration of B?

Hannah_1G

Does the initial mass of the drug replace the concentration in the rate law equation for solving for the left over mass? $[A]_{t}= [A]_{0}e^{-k_{r}t}$
Would I use this equation in 7B.1 to solve for how much drug is left?

Hannah_1G

If the rate constant and initial molarity are given for a first order reaction and so is a temperature at which the reaction is happening, does the temperature factor in to the rate of the reaction?

Hannah_1G

Kimberly Koo 2I wrote:An electrolytic cell converts electrical energy into chemical energy, while a galvanic cell converts chemical energy into electrical energy.

What exactly would an electrolytic cell do? Is it not generating a voltage charge like a galvanic cell since the energy is turned into chemical?

Hannah_1G

How do you tell which order the reaction rate is at? Is it always given? What is it dependent on? I don't very much understand this concept at all, please explain! Thank you!

Hannah_1G

What is the k_r constant? The book just explains it as a proportion of the initial rate of consumption? I am having a hard time understanding this concept.

Hannah_1G

Cl 2 (g) $\rightarrow$ HClO(aq) + Cl 2 (g). I don't know how to find the reduction half of this problem, it shows Cl going to Cl which isn't a loss or gain of electrons.

Hannah_1G

How does oxidation number of an element relate to how many electrons it will lose or gain? I am confused on how to calculate when in acidic or basic solutions it changes the net charges.

Hannah_1G

Can someone explain the difference between the two? I don't understand what an electrolytic cell is and how it could be different than a galvanic cell.

Hannah_1G

Hi, is there a way to separate and count posts made in 14A from 14B as to see how many you've done for each class rather than in total?

Hannah_1G

How do you find n?

Hannah_1G

Should we check and balance each redox half reaction before trying to calculate gibbs free energy? For example 6L.1: 2 Ce⁴⁺ (aq) + 3 I^- (aq) $\rightarrow$ 2Ce³⁺ (aq) + I₃^- (aq), E cell ° = +1.08 V. Before calculating gibbs, would I need to balance the reaction?

Hannah_1G

What is the difference between $\Delta G and [tex]\Delta G ^{\circ}$ ? Why can $\Delta G ^{\circ}$ +RTlnQ = [tex]\Delta G?

Hannah_1G

How do we know this reaction is at equilibrium? Shouldn't only Q be used?

Hannah_1G

When calculating the heat required for ice to change into water vapor, do the steps need to be broken down into ice to liquid and liquid to water vapor and taking the sum of that since the heat capacities are different at different phases?

Hannah_1G

Subtracting the enthalpy of formation of the product from the reactants generates a positive number, but the answer is negative. Can someone please explain why this is the case?

Hannah_1G

How do you go about solving this? The moles of liquid methane are given and the heat required. The only equation I know for enthalpy of vaporization is $\Delta$ H_vap= H_m(vapor) - H_m(liquid).

Hannah_1G

The book only has partial answer to the question, the temperature it gives is for constant volume not the pressure. I think I did it correctly.

Hannah_1G

I tried to solve the first part of this problem using Cp,m= 5/2 R and q= 765J and finding the change in temperature with q/(moles)(Cp,m) but I keep getting the final temperature as 343K when the book says 373 K.

Hannah_1G

How do you find moles for the equation when temperature, pressure, and volume are given?

Hannah_1G

If the system has a given pressure and another pressure is acting on it doing work, do you ignore the systems initial pressure to solve for work? For reference, 4B.13 says calculate the work for a gas sample in a piston assembly with T=305 K, P=1.79 atm, and V=4.29 L: (a) irreversible expansion agai...

Hannah_1G

The question tells to calculate the pH of the diprotic acids and to ignore the second deprotonation if approximation is justified, how would you know to ignore or not?

Hannah_1G

Are Ka and Kb always equal when Kw is given? I don't know how else to solve for the concentration of H30+ and OH- when only the value of Kw was given. For reference, homework problem 6A.21

Hannah_1G

If the log[H30+], without the negative sign, is already positive, is it wrong? For example, a concentration of 3.1 M results in a pH= -.49, using -log(3.1).

Hannah_1G

I thought the rule for volume decrease is that the side with less moles will be favored; however, in 5.39 the volume was halved and the reactant which has more moles in equation, I calculated it to have increased in concentration.

Hannah_1G

In 5.35 theres a partial pressure/ Kpa vs time graph and you have to figure out how to balance the equation as well as calculate K from it. How are we supposed to read this?

Hannah_1G

How is X2(g) $\rightleftharpoons$ 2X(g), where X is a halogen, affected by temperature? Does it favor reactant or product?

Hannah_1G

What is the rule for increasing or decreasing pressure and its affect on shifting the reaction?

Hannah_1G

Does increasing or decreasing the concentration of a product affect the concentration of another product? For example, for the reaction 4NH3(g) + 5O2(g) $\rightleftharpoons$ 4NO(g) + 6H20(g), does increasing the concentration of NO affect the concentration of H20?

Hannah_1G

How does pressure increasing or decreasing change the concentration of products or reactants in equilibrium? Does a change in pressure for a reactant affect another reactant in the reaction?

Hannah_1G

Not sure what I am doing wrong, but in solving the concentrations using an ice table I am getting a larger change in concentration than what was initially there.

Hannah_1G

Can someone explain what this means in terms of expansion? How can work be irreversible?

Hannah_1G

I cannot get the correct answer. I am using the area of a cylinder with .15 m as radius and .2 m as height times the height to get the volume times 2 atm as the pressure.

Hannah_1G

What formula is used to calculate the change in temperature from copper at 100 degrees C placed in water at 22 degrees C? I don't know how to begin this problem

Hannah_1G

How do you calculate the change in concentration when only the products are used in the reaction and the equilibrium concentration is given? Initial concentration of .2 M of NH3 with H2S and K= 1.6 x 10^-4

Hannah_1G

How does K= 41 go to K= 1.7 x10³ when the reaction has twice as many moles in reactants and products? For reference the original reaction is N2 + 3H2 = 2NH3 and K= 41 and the reaction is changed to 2N2 + 6H2 = 4NH3.

Hannah_1G

If the reaction is homogeneous with gas phase but the question is in terms of concentration and gives the moles of the reactants and products, is pressure ignored?

Hannah_1G

The filling of the octets is the most important aspect - double and triple bonds come in later. Double bonds should be used when both the central and attached atom has an extra lone pair each, and if the formal charge conditions are most favorable. I am not sure what you are talking about regarding...

Hannah_1G

When figuring out the lewis structure of an acid or base, should you stay away from double or triple bonds even if it stabilizes the molecule? Do the bonds make it have less acid/base characteristic. In all of the examples I've seen of finding if a molecule is an acid or base from the lewis structur...

Hannah_1G

The book draws SO3 (hw 6.5) with one double bond and two single bonds, but it is more unstable than SO3 having three double bonds. Does it have to do with SO3 acting as an acid or base?

Hannah_1G

Do we need a reverse arrow in all acid and base chemical equations? $\rightleftharpoons$

Hannah_1G

CO3 with a -2 charge is either a mono or bidentate ligand, according to the book. Is it possibly monodentate because the molecule is small?

Hannah_1G

How do you figure out how many sites a ligand can bind to on a metal?

Hannah_1G

If the lone pairs are on opposite sides then they cancel out. An example of this would be XeF4 since it is square planar and all the dipole movements from the Fs and electron pairs are negated. So you need to know the molecular shape before figuring out if the lone pairs align to create a dipole mo...

Hannah_1G

Will a strong acid have a strong conjugate base and the same for the opposite?

Hannah_1G

If the product of an acidic reaction still has hydrogens in its molecule is it commonly a weak acid? Like acetic acid, CH3COOH after dissolving in water its left as CH3CO2-, whereas HCl is left as Cl-.

Hannah_1G

In lecture, I'm pretty sure Lavelle said that CO was a ligand and I'm confused as to how that is so.

Hannah_1G

Can someone explain what a ligand is and what it does?

Hannah_1G

are all resonance structures delocalized electrons?

Hannah_1G

How do you total in the strength in a bond when factoring how many bonds and the s- orbital characteristic of it? If I'm not mistaken having a hybridized orbital sp is stronger than sp2 but is a double bond stronger than a single bond of 2p-2p?

Hannah_1G

How do you figure out if lone pairs align to create a dipole moment?

Hannah_1G

How would you determine where the lone pairs on a central atom would be in a molecular shape? How would you know if they align to create a dipole moment or cancel eachother out?

Hannah_1G

If the electrons are localized, then it's how many electron density regions it has. So like CH4, the carbon has 4 electron density regions, so it has sp3.

Hannah_1G

Unhybridized orbitals are used to make pi bonds

Hannah_1G

Is it correct that resonance structures have unhybridized orbitals since the electrons are delocalized?

Hannah_1G

why is having a sp hybridization stronger than sp2?

Hannah_1G

Is it possible for a sigma bond to be unhybridized?

Hannah_1G

Can someone simply explain hybridization for me? Can't understand what it means and the 4 different hybrid orbitals.

Hannah_1G

How do you know when an acid and base reaction forms ions or compounds of eachother? Like Ca(OH)2 + 2HCN forms Ca(CN)2 + 2H2O but 2Na + 2OH- + H2S forms 2H2O + 2NA+ + S2-

Hannah_1G

How do you know when the shape is being asked for, for instance, seesaw or its asking for tetrahedral? What are the differences between those two different categories of naming the molecule shape? Sorry if this isn't clear, I just don't know if I should be predicting the molecule as t-shaped or trig...

Hannah_1G

You should look at the OVERALL characteristic. This molecule is polar overall because of the electronegativity difference between the C and Cl. Assuming that this molecule is interacting with only itself, dipole induced-dipole is not possible because it requires a non polar molecule which ClCH3 is ...

Hannah_1G

If you are referring to diethyl ether to having dipole-dipole intermolecular forces and water to have hydrogen bonding, then water (hydrogen bonding) would have a stronger intermolecular force because hydrogen bonds are stronger than dipole-dipole bonds. Thank you this is what I was asking! Do you ...

Hannah_1G

Are tetrahedral and trigonal pyramidal the same?

Hannah_1G

Lone pairs on central atom cause the expected bond angles to be slightly less?

Hannah_1G

Do lone pairs not on the center atom account for shape? For example HCN

Hannah_1G

Would hydrogen bonding (in water) be stronger than one dipole moment (diethyl ether)?

Hannah_1G

Would a double bond create a higher melting point than a dipole moment?

Hannah_1G

How does butanol have a higher melting point than diethyl ether when they have the same atoms?

Hannah_1G

But how would you count the amount of hydrogen bonding sites?

Hannah_1G

Are possible hydrogen bonding sites on every H and O,N,F electron lone pairs in a molecule? And the amount of lone pairs also tells how many hydrogen bonds could happen on an atom in a molecule?

Hannah_1G

How do you separate the two different forces? How does ClCH3 have dipole-dipole interactions rather than dipole-induced dipole?

Hannah_1G

Is hydrogen bonding only possible in a molecule with hydrogen already in it? Is it impossible for that type of interaction to occur on molecules containing O,N, or F with lone pairs that aren't already bonding to hydrogen?

Hannah_1G

In the answer key for the mini dino nuggets, the dipole moments in question 2a are going towards the negative partial charge when in the textbook it says to go towards the positive charge. What would be correct?

Hannah_1G

I forgot to times it by Avogadro's constant to find amount of photons. But this number should be multiplied by two?

Hannah_1G

For reference, I am doing 1B.9, which gives the wavelength of the light and watts of the light and I am stumped on how many photons are being emitted in 2 seconds. I used E=hv to find the energy of a singular photon and then I divided that by the watts which gave me the answer in the back of the boo...

Hannah_1G

If the question is asking this but in a 2 second interval would you do the same but times it by 2?

Hannah_1G

1B.7 is asking for the energy emitted by a sodium atom when it generates a photon and for the energy of 5.00 mg of sodium emitting light. Do I think of the excited sodium atom as a photon in this problem? As in the formula E=hv applies to this question, not the kinetic energy of an electron. Then, I...

Hannah_1G

Brittney Hun 1K wrote:So I used two different equations to derive the energy because it's not asking for the energy of an electron, which is what the kinetic energy formula finds. I used E=hv, but found v first using v=c/lamda for part a.

What is the question asking for?

Hannah_1G

Never mind I know that doesn't work because the v in that formula is for the speed of the electron. Is the work function of the atom supposed to be given to find this if only wavelength of light is provided? I should be using (hc)/ $\lambda$ - $\phi$ = E_k

Hannah_1G

If a problem (1B.7) is asking for the energy emitted by an atom when it generates a photon and the wavelength of the photon ejected is given, would I use the E_k= 1/2 m_e x v² formula?

Hannah_1G

What is being asked by finding the formula units and number of molecules from moles of a molecule? For reference Fundamentals E.21 asks to calculate the amount of moles, amount of molecules and formula units from 10 g of Al2O3.

Hannah_1G

Is it correct to divide the amount of atoms in a sample by the molar constant to find the amount of moles?

Hannah_1G

Thank you! So this question is asking for what possible ions follow those configurations and have a 2+ charge?

Hannah_1G

The question asks which M2+ ions are expected to have the following ground-state electron configurations: a) [Ar]3d7 b) [Ar]3d6
I'm confused by what the question is asking and how the electron configuration can change for this ion?

Hannah_1G

205296774 wrote:Our homework and units aren't broken up by week. The quantum unit is multiple weeks long so the page with the key concepts and hw problems apply to this week, too.

Hope this helps!

Did Lavelle say that we can use chemical bond problems for this weeks homework?

Hannah_1G

The octet rule is violated in compounds with more than eight electrons assigned to their valence shell. These are called expanded valence shell molecules. Such compounds are formed only by central atoms in the third row of the periodic table and beyond that have empty d orbitals in their valence sh...

Hannah_1G

How do you figure out the lewis structure of BrF3 when they share 24 valence electrons?

Hannah_1G

In the homework it asks for the ground state electron configuration of ions, does ground state mean that the ions need to be changed to a neutral atom?

Hannah_1G

In the second part of G.17 it asks for the mass of CuSO4 5H20 that must be used to prepare 250 mL of .2 M CuSO4(aq). I am very confused by what to do with the water molecule in this problem, I don't know how to start solving this.

Hannah_1G

I am having trouble with this concept as well, the amount of individual moles in a molecule has the same ratio as moles of the molecule? So 2 nitrogen moles are always in 1 mole of NH4NO3?

Hannah_1G

In homework problem G.5 the question says there is 2.111 g of sodium carbonate (Na 2 CO 3 ) and you have to find the molarity in a solution, is it possible to find the mole ratio of the molecule and apply it to the elements? The molar mass of sodium carbonate is 105.81 gmol -1 , so in a sample of 2....

Hannah_1G

No, the number of sig figs can vary because it is based on the least amount of sig figs present in the problem. However, any conversion factors do not count when determining the number of sig figs. Thank you this helped a lot. I was looking for the homework question to mention how many sig figs to ...

Hannah_1G

The question asks how much can Br₂ can be produced from .30 moles of ClO₂ when the balanced reaction is given. Is it simple enough to assume that 6 moles of ClO₂ produces one mole of Br₂ so .30/6 would be the amount of Br₂ in moles produced?

Hannah_1G

If the question doesn't mention sig figs, should I not worry about the precision of the answer then?

Hannah_1G

The question gives how many carbon atoms are in a molecule of DNA and to calculate in moles how many atoms of carbon there are. Is this asking to divide the number of atoms by moles to be in terms of mole or to multiple the amount of carbon by Avogadro's constant to find the true amount of atoms? So...

Hannah_1G

For the homework are we supposed to be using a set significant figure number?

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