CHEMISTRY COMMUNITY

Ellis Song 4I

The k for a reversed reaction is 1/k

Ellis Song 4I

After taking Dr. Lavelle's 14A and 14B class, what was your favorite chem topic so far?

Ellis Song 4I

Do we need to know about the collision theory and the equations associated with it that are in the textbook?

Ellis Song 4I

Can someone explain and summarize what the graphs for each order reaction looks like and what they mean?

Ellis Song 4I

The half-life of A in a second-order reaction is 50.5 s when [A]0 = 0.84 mol/L. Calculate the time needed for the concentration of A to decrease to (a) one-sixteenth (b) one-fourth; (c) one-fifth of its original value.

Can someone please explain this problem

Ellis Song 4I

Calculate the potential of a cell constructed with two nickel electrodes. The electrolyte in one compartment is 1.0 m Ni(NO3)2(aq). In the other compartment, NaOH has been added to a Ni(NO3)2 solution until the pH = 11.0 at 298 K. See Table 6I.1. How do you determine which is the anode and which is ...

Ellis Song 4I

A tin electrode in 0.015 m Sn(NO3)2(aq) is connected to a hydrogen electrode in which the pressure of H2 is 1.0 bar. If the cell potential is 0.061 V at 25 C, what is the pH of the electrolyte at the hydrogen electrode?

Where should you start with this problem?

Ellis Song 4I

This question asks us to order metals by increasing strength as a reducing agent but how do we determine this? I know that the more negative the standard reduction potential, the stronger it would be as a reducing agent but when I looked up the reduction potentials in the back of the book, there wer...

Ellis Song 4I

A student was given a standard Cu(s)uCu21(aq) half-cell and another half-cell containing an unknown metal M in 1.00 M(NO3)2(aq) and formed the cell M(s)|M+(aq)||Cu2+(aq)|Cu(s). The cell potential was found to be -0.689 V. What is the value of E(M2+/M)? The solutions manual for this problem flips the...

Ellis Song 4I

It should only be the end of thermodynamics and through electrochemistry. Kinetics should not be on test 2 at all.

Ellis Song 4I

When given a galvanic cell, how do you determine which is the anode and which is the cathode? Is it just based on the anode being written on the left side and cathode being written on the right?

Ellis Song 4I

A reaction used in the production of gaseous fuels from coal, which is mainly carbon, is C(s) 1 H2O(g) Δ CO(g) 1 H2(g). (a) Evaluate K At 900 K, given that the standard Gibbs free energies of formation of CO(g) and H2O(g) at 900 K are 2191.28 kJ/mol and 2198.08 kJmol, respectively. (b) A sample of g...

Ellis Song 4I

This question asks us to depict the progress of the reaction I2(g) -> 2I(g) graphically. Can someone explain how to do this?

Ellis Song 4I

I don't recall Dr. Lavelle covering these topics very in depth in class. Will there be problems on them on Test 2?

Ellis Song 4I

Is the E cell given to us or is it in an appendix or will be have to solve for it?

Ellis Song 4I

It means platinum and is used as a inert conductor as electrode to transfer electrons. Graphite can also be used the same way.

Ellis Song 4I

I believe we can assume that the oxidation number for Oxygen will be -2 and for Hydrogen it will be +1

Ellis Song 4I

I'm a confused on how to balance a redox reaction in basic solution. Are we supposed to use OH- like we use H+ in a reaction in acidic solution?

Ellis Song 4I

How do you find oxidation numbers?

Ellis Song 4I

Does Lavelle curve his tests at all? Can we expect a curve for the midterm?

Ellis Song 4I

q = J
w = J
$\Delta U$ = J
$\Delta H$ = J/mol, J/g
$\Delta S$ = J/K, J/°C
$\Delta G$ = J
k/Q = no units

Feel free to correct me or add on

Ellis Song 4I

Why are the balanced chemical equations for this unit have fractional coefficients rather than integers? Would doing the problem with the whole number coefficients change the answer because the ratios would still be the same.

Ellis Song 4I

What exactly is $\Delta U$ ? I know it means internal energy but I'm not sure what that means.

Ellis Song 4I

Calculate the standard entropy of vaporization of water at 85 C, given that its standard entropy of vaporization at 100 C is 109.0 J/Kmol and the molar heat capacities at constant pressure of liquid water and water vapor are 75.3 J/Kmol and 33.6 J/Kmol, respectively, in this range. I don't know wher...

Ellis Song 4I

Is the equation for work always negative even if we are calculating work done on the system?

Ellis Song 4I

After finding the enthalpy for the reaction, you need to find how much energy is released per mole of TNT. The reaction requires 4 moles of TNT, but since you want the energy per mole of TNT, you divide the reaction enthalpy by 4. Now, all you have to do if multiply this energy by the density of TN...

Ellis Song 4I

The enthalpy of formation of trinitrotoluene (TNT) is -67 kJ/mol, and the density of TNT is 1.65 g/cm^3. In principle, it could be used as rocket fuel, with the gases resulting from its decomposition streaming out of the rocket to give the required thrust. In practice, of course, it would be extreme...

Ellis Song 4I

Do we have to memorize the chart on page 266 which has the different coefficients to find the heat capacities of ideal gases? I know we learned (3/2)R and (5/2)R for individual atoms but the book also gives us equations for linear and nonlinear molecules. Homework problem 4C.5 asks about these and i...

Ellis Song 4I

When do we use $q=nC\Delta T$ vs. $q=C\Delta T$

Ellis Song 4I

What topics will the midterm cover? Will we have to know all of Thermodynamics as well?

Ellis Song 4I

You can find this number in the constants and equations paper. It converts 1 Latm to 101.325 J.

Ellis Song 4I

Calculate the final temperature and the change in enthalpy when 765 J of energy is transferred as heat to 0.820 mol Kr(g) at 298 K and 1.00 atm (a) at constant pressure; (b) at constant volume. Treat the gas as ideal. For part a the solutions manual says q=(5.025 g/83.80 g/mol)(25C - 97.6C)(20.8 J/m...

Ellis Song 4I

The temperature is interchangeable because Kelvin and Celsius are to the same scale. So one degree change of Celsius is one degree change in Kelvin and vice versa

Ellis Song 4I

Open: can exchange matter and energy
Closed: can exchange only energy
Isolated: can not exchanged anything

Ellis Song 4I

What section of the textbook is reaction enthalpies in? I started reading Focus 4 and didn't see it.

Ellis Song 4I

I am not clear on what Dr. Lavelle was explaining about steam burns. Can someone explain it to me?

Ellis Song 4I

If only Ka or Kb is given and the temperature is not stated, can we assume that it is at 25 Celsius and use 1.0x10^-14 to find the constant we need?

Ellis Song 4I

Calculate the pH of b) 0.055 M AlCl3. The K value isn't given and is not in the tables in the textbook. How are we supposed to solve this?

Ellis Song 4I

Calculate the pH, pOH, and percentage protonation of solute in each of the following aqueous solutions: a) 0.057 M NH3; b) 0.162 M NH2OH; c) 0.35 M (CH3)3N; d) 0.0073 M codeine, given that pKa of its conjugate acid is 8.21. I'm confused on how exactly to do this problem. Are we supposed to have K va...

Ellis Song 4I

When the concentrations of H and OH are 1.5 M, isn't the pH and pOH negative?

Ellis Song 4I

Can someone explain exactly why the reaction shift is dependent on the number of moles on each side of the reaction?

Ellis Song 4I

Cl2 is more stable because it has a lower K value. In the reaction Cl2 -> 2Cl, the reactant (Cl2) would be more greatly favored which makes it than the reaction with F2 and thus it is more stable

Ellis Song 4I

Solids and liquids do not affect because their concentrations do not change.

Ellis Song 4I

What exactly is just K compared to Kc and Kp

Ellis Song 4I

(a) In an experiment, 2.0 mmol Cl2(g) was sealed into a reaction vessel of volume 2.0 L and heated to 1000. K to study its dissociation into Cl atoms. Use the information in Table 5G.2 to calculate the equilibrium composition of the mixture. (b) If 2.0 mmol F2 was placed into the reaction vessel ins...

Ellis Song 4I

Q and K are calculated the same but Q is the value at any point during the reaction while K is the value at equilibrium.

Ellis Song 4I

Why does the equilibrium constant, K, not have units?

Ellis Song 4I

K values do not have units

Ellis Song 4I

The concentration of the reactants and products are not necessarily the same; they are just at specific concentrations that allow the reaction to be at equilibrium where both the reaction and reverse reaction occur at an equal rate.

Ellis Song 4I

P means Partial Pressure and the brackets [] mean concentration

Ellis Song 4I

Do we have to memorize the sheet that Dr. Lavelle provided with how to name ligands for the final?

Ellis Song 4I

Decide whether an aqueous solution of each of the following salts has a pH equal to, greater than, or less than 7. If pH < 7 or pH > 7, write a chemical equation to justify your answer. e: AlCl_{3} f: Cu(NO_{3})_{2} I'm not sure how to go about doing these and I don't understand the solution...

Ellis Song 4I

Why is the pH of KBr neutral but the pH of KF in part c is basic?

Ellis Song 4I

Why is the pH of KBr neutral but the pH of KF in part c is basic?

Ellis Song 4I

Why does $H_{2}PO_{4}^{-}$ lose another H to become $HPO_{4}^{2-}$ ? Why would it not gain a H to become neutral?

Ellis Song 4I

Will there be problems on coordination compounds on the final? I feel we did not cover it much in class and there were very few homework problems on it. What kinds of questions could there be?

Ellis Song 4I

How often do I tell chemistry jokes??? Periodically

Ellis Song 4I

What is the best way to go about studying for the final? Will there be practice finals released?

Ellis Song 4I

What is "en" and "edta" in part c and d of this problem?

Ellis Song 4I

I'm having trouble naming compounds. I'm mostly struggling with figuring out how many molecules and what the roman numeral means.

Ellis Song 4I

Do we have to memorize all the rules for naming ligands?

Ellis Song 4I

Part b of this questions asks us to Identify the composition of the bonds and the hybridization of each lone pair—for example, by writing s (H1s,C2sp 2). What do they mean by lone pair? The Lewis structure I drew only has lone pairs around the oxygen for this molecule so do they just want the inform...

Ellis Song 4I

Part b of this problem asks us to determine if any of the molecules are radicals. I don't think any of the molecules are radicals but I don't have the solutions manual so I am not sure. Are any of the molecules radicals?

Ellis Song 4I

I'm a bit confused on what exactly ligands are. Is ligand just a name for a particular segment of a molecule?

Ellis Song 4I

What kinds of questions could we get asked and tested on for sigma and pi bonds? There weren't many problems in the homework about it. Will we just be asked how many of each type of bond there are in a molecule?

Ellis Song 4I

Bond angles aren't something that we calculate, we just have to memorize them

Ellis Song 4I

VSPER model only considers regions of high electron concentration not the actual concentration which is why multiple bonds are treated as a single region of high electron concentration

Ellis Song 4I

You can tell if there are lone pairs based on how the structure is drawn. For part a there has to be lone pairs because of how the other bonds are at an angle which means they are being repelled by a lone pair. For part b there is no obvious repulsion but there can still be lone pairs if there was a...

Ellis Song 4I

Will we have to memorize all the different names of the shapes and the bond angles?

Ellis Song 4I

Suggest, giving reasons, which substance in each of the following pairs is likely to have the higher normal melting point: c) CHI3 or CHF3 The solutions manual says CHI3 would have a higher melting point because it has stronger London Dispersion forces but how is the strength of London Dispersion de...

Ellis Song 4I

I'm confused on how to know which way to draw dipole arrows and when to draw them.

Ellis Song 4I

Will Test 2 include all the content we've learned thus far or just what we have learned after the midterm?

Ellis Song 4I

How exactly is bond strength determined? I know it is dependent on the number of bonds but how do you tell the difference of bond strengths between different atoms?

Ellis Song 4I

Do we need to memorize which bonds correspond to which differences in electronegativity?

Ellis Song 4I

How do you know which atoms to form a double bond with when drawing a lewis structure? For example, why does the double bond form between O and N instead of F and N in the molecule ONF

Ellis Song 4I

How do you determine the number of valence electrons for transition metals?

Ellis Song 4I

What is the purpose of formal charge? I know how to calculate it but what exactly is it for?

Ellis Song 4I

Is there a quicker way to draw resonance structures or is the only way to just redraw the structure with the different double bonds?

Ellis Song 4I

The number of valence electrons is determined by the group number. For groups 13-18, the number of valence electrons is the number in the ones place.

Ellis Song 4I

Which M $3^{+}$ ions (where M is a metal) are predicted to have the following ground-state electron configurations:
(a) [Ar]3 $d^{6}$
(b) [Ar]3 $d^{5}$

For this problem, why does the solutions manual say that a is Cobalt and b is Iron instead of Iron and Manganese, respectively?

Ellis Song 4I

For this problem all you really have to look at is whether or not the electrons are put into orbitals properly. There should be one electron in each orbital before pairing all in the same direction and s- orbitals should fill completely before moving on to p- orbitals

Ellis Song 4I

For me the easiest way to find unpaired electrons is to think about how they would be put into orbitals and how you have to put an electron in each orbital before you start pairing. Just figure out the number of valence electrons and put them into orbitals using the arrows.

Ellis Song 4I

What is the equation to determine effective nuclear charge?

Ellis Song 4I

- Atomic radii increase down a group and decrease across a period - Ionic radii increase down a group and decrease across a period, cations are smaller than parent and anions are larger - Ionization energy decreases down a group and increases across a period - Electron affinity is high for elements ...

Ellis Song 4I

3d should come before 4s for atoms with an atomic number after 20

Ellis Song 4I

For this problem you use the equation $\Delta p\Delta x=\frac{h}{4\pi}$ but you break up $\Delta p$ into (mass of the electron)x $\Delta v\Delta x= \frac{h}{4\pi }$

You can then plug in all your known variables and solve for $\Delta v$

Ellis Song 4I

Balmer Series: visible light, n1 = 2
Lyman Series: ultraviolet light, n1 = 1

Ellis Song 4I

What is the minimum uncertainty in the speed of an electron confined within a lead atom of diameter 350. pm? model the atom as a one-dimensional box with a length equal to the diameter of the actual atom. I know that I am supposed to use the uncertainty equation for this but I am not sure where to b...

Ellis Song 4I

32 W = 32 J/s in 2 sec -> 64 J Use the equation E = hc/(wavelength) to find the energy per photon. You should get 4.73 x 10^-19 J/photon Divide 64 J by that number to get the number of photons -- 1.35 x 10^20 photons To find how many moles that is you just divide by Avogadro's number and should get ...

Ellis Song 4I

On Lavelle's website there is a link for a pdf with all the constants and equations and the speed of light used in that is 2.99792 × 10^8 m/s so I assume that using 2.998 would be fine

Ellis Song 4I

The lines are grouped into series based on the lower energy level the electron drops down to and how much energy they’re emitting

Ellis Song 4I

Hi Ellis! This is Ariel. Here's a general list from my notes: c = λ ν -- Used to calculate wavelength/frequency E(photon) = h ν -- Used to calculate energy per single photon -- Bohr Frequency Condition: v = ∆E/h; used to calculate frequency E(photon) = Work Function/Threshold Energy + EK EK =(1/2)m...

Ellis Song 4I

Ryan Chew 1C wrote:Is there a specific example or equation you're having trouble with? I'm not sure if I can describe all of them.

Maybe for problem 1a.15 I’m confused about the Rydberg equation.

Ellis Song 4I

1A.15 In the ultraviolet spectrum of atomic hydrogen, a line is observed at 102.6 nm. Determine the values of n for the initial and final energy levels of the electron during the emission of energy that leads to this spectral line. Reading this question, I have no idea where to begin. Is the questio...

Ellis Song 4I

I’m having some trouble with all the equations that we’ve learned so far. Can someone list them and explain when we’re supposed to use each one?

Ellis Song 4I

Do we need to memorize the range of wavelengths that each type of radiation have and what order they go in the electromagnetic spectrum. In question 1A 9 in the homework, we are asked to fill out the chart and then determine the type of radiation and events for each line. Are we allowed to refer to ...

Ellis Song 4I

What is the rule for naming formulas with metals? For example, in L39, they ask us to name the oxide and the answer is tin(IV) oxide. Where exactly does the roman numeral come from and how do we determine it?

Ellis Song 4I

the way it is written in the solutions manual is a bit confusing. What is really happening is that they are dividing the mass of the element by the total molar mass of the compound to get the fraction/decimal of that element. They then multiply by 100% to convert that decimal into a percentage.

Ellis Song 4I

To get the empirical formula from the molecular formula, you divide the subscripts by their common factor because the empirical formula is the most simplified version of the ratio of the atoms.

Ellis Song 4I

First you find the molar mass of (OH)2 by adding together the molar mass of oxygen and hydrogen then multiplying by 2. Then you subtract that from the given molar mass, 74.10, to find the molar mass of the metal. The number you get is 40.08 g/mol which is the molar mass of Calcium - you must refer t...

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