CHEMISTRY COMMUNITY

Sean Phen

Thank you so much, Dr. Lavelle!

Sean Phen

How do you identify the proper units for the rat constant, k, for each reaction order?

Sean Phen

What are the differences between Q and K?

Sean Phen

How do you solve for Kc, equilibrium concentration?

Sean Phen

Can someone explain the E naut value and what it defines as? I am just slightly confused.

Sean Phen

Once you compute the order of each reactant, the rate is equal to k multiplied by the concentration of each reactant to the power of its order. So it would look like rate = k([A]^l)([B]^m)([C]^n) are the l, m, and n the order of the reactants? yes! l is the order for reactant A, m --> B, n --> C Th...

Sean Phen

Jasmine Ho 3I wrote:Once you compute the order of each reactant, the rate is equal to k multiplied by the concentration of each reactant to the power of its order.
So it would look like rate = k([A]^l)([B]^m)([C]^n)

are the l, m, and n the order of the reactants?

Sean Phen

How do you write the rate law for the reaction where k is the rate constant? I have attempted this problem numerous times, but I still can't get it right.

Sean Phen

"The rate constant for this first‑order reaction is 0.870 s−1 at 400 ∘C.
A⟶products

How long, in seconds, would it take for the concentration of A to decrease from 0.730 M to 0.400 M?"

How do you determine the time for the decrease in concentration of A?

Sean Phen

"Consider the mechanism.

step 1: AB+C⟶A+BC
step 2: AB+BC⟶AB2+C
overall: 2AB⟶A+AB2"

How do you determine which species is an intermediate and which is a catalyst? Any tips or tricks of figuring out which is which?

Sean Phen

Hello, I get confused on which formula to use because there are so many. Is there any tip or tricks of ways to know which formula to be using?

Sean Phen

"The rate of the given reaction is 0.600 M/s.
A+4B⟶2C

What is the relative rate of change of each species in the reaction?"

What is the easiest method of solving for the relative rate of change? I get confused on how to do it.

Sean Phen

The step up sessions are tremendously helpful because they review all of the concepts that will be on the final and also gives examples to support those concepts as well. I also believe that the textbook problems are extremely helpful as well.

Sean Phen

I find that handwriting notes is the best at remembering concepts. For tests, studying the homework problems has helped tremendously because many of them are on the tests. I am not sure how the final will be, but it is good to study the homework questions.

Sean Phen

"Consider the generic redox reaction shown. X(s)+Y+(aq)↽−−⇀X+(aq)+Y(s) If the coefficients in the redox reaction are doubled, how will the given quantities be affected for a voltaic cell under nonstandard conditions?" I was confused on how to determine how the quantities would be affected.

Sean Phen

I had trouble with determining if a reaction is spontaneous or nonspontaneous. Can anyone help me with this concept?

Sean Phen

How do you determine which is the best oxidizing agent and which is the poorest oxidizing agent?

Sean Phen

"Complete the half‑reactions for the cell shown, and show the shorthand notation for the cell. The electrode on the left is the anode, and the one on the right is the cathode."

How do you tell which is the correct half-reaction for both cathode and anode?

Sean Phen

I keep on mixing up anode vs cathode. How can you tell them apart? Does anyone have a strategy of remembering the differences?

Sean Phen

If we are a Chem 14B student, are we only restricted to posting in the Chem 14B section or are we allowed to also post a question in the Chem 14A section if one of my questions relate to a topic in Chem 14A?

Sean Phen

How do you calculate the Kb of a solution if you already know the Ka value? I know that I have to subtract the Ka value by 14, but sometimes it comes out wrong. I am confused on why that is.

Sean Phen

What are some good rules to remember which is the oxidizing agent and which is the reducing agent?

Sean Phen

4A-13: "A constant-volume calorimeter was calibrated by carrying out a reaction known to release 3.50 kJ of heat in 0.200 L of solution in the calorimeter (q=−3.50kJ), resulting in a temperature rise of 7.32 °C. In a subsequent experiment, 100.0 mL of 0.200 M HBr(aq) and 100.0 mL of 0.200M KOH(...

Sean Phen

How do you solve for K in the van't hoff equation? I was confused on how to get the ln out and isolate K.

Sean Phen

What is the difference between irreversible and reversible work functions?

Sean Phen

"Based on the calculated ΔSvap values, arrange the liquid samples in order from most ordered to least ordered.

C2H5OH, C3H6O, C5H12"

How do you know what is most ordered and what is least ordered?

Sean Phen

"Calculate the standard molar entropy of vaporization of water at 33.0 °C , given that its standard molar entropy of vaporization at 100.0 °C is 109.0 J⋅K−1⋅mol−1 and the molar heat capacities at constant pressure for liquid water and water vapor are 75.3 J⋅K−1⋅mol−1 and 33.6 J⋅K−1⋅mol−1 , resp...

Sean Phen

I just want to double check. Is our Sapling Homework Week 5/6 due on Wednesday, 2/17 instead of today?

Sean Phen

Start by dividing the energy supplied by the number of moles to find the molar enthalpy of vaporization for the first part. Then, you can divide that value by the temperature, T, to get the molar entropy of vaporization for the second part. Then just repeat this for the other compound. Hope this he...

Sean Phen

"Three liquid samples of known masses are heated to their boiling points with the use of a heater rated at 600.0 W . Once the boiling points of each sample are reached, the samples are heated for an additional 5.79 min , which results in the vaporization of some of each sample. After 5.79 min ,...

Sean Phen

Why can't you have phase changes in (positive H and negative S) and (negative H and positive S)?

Sean Phen

What lectures are covered in midterm 2?

Sean Phen

"Suppose a 3.069 g sample of a second compound, compound B, is combusted in the same calorimeter, and the temperature rises from 25.61 ∘C to 28.68 ∘C. What is the heat of combustion per gram of compound B?" For the heat of combustion, I kept on getting 8.13 kJ/g. I am not sure why this is ...

Sean Phen

You would put the negative sign on the side which is exothermic or losing the heat. The one with the higher temperature is exothermic (losing heat), and the one with the lower temperature is endothermic (gaining heat).

Sean Phen

I think you are a little off. The part of your equation that is wrong is the 6.01 * 10^3J/mol. You need to figure out the heat required to melt ice which is moles of ice multiplied by delta H f of water.

Sean Phen

"If you combine 440.0 mL of water at 25.00 ∘C and 100.0 mL of water at 95.00 ∘C, what is the final temperature of the mixture? Use 1.00 g/mL as the density of water." I know that you have to make them equal to each other, but how do you know which side of the equation you make negative and...

Sean Phen

Why does q equal to delta U?

Sean Phen

This might be a dumb question, but is Sapling Week 3 & 4 homework due today or next Sunday?

Sean Phen

"Carbon disulfide can be prepared from coke (an impure form of carbon) and elemental sulfur. 4C(s)+S8(s)⟶4CS2(l)ΔH∘=+358.8 kJ Calculate the amount of heat absorbed in the reaction of 169 g of carbon with excess sulfur. Calculate the amount of CS2 produced when 397 kJ of heat is absorbed." ...

Sean Phen

How do you know when you have to use either Ka or Kb in calculating the pH of a salt solution?

Sean Phen

What are the rules for when to make X negligible?

Sean Phen

How do you know if one side is + X and the other side is -X for an ICE table equation?

Sean Phen

Till what lecture is the midterm 1 covering?

Sean Phen

"Muscles produce lactic acid, CH3CH(OH)COOH(aq) , during exercise. Calculate the percent ionization (deprotonation), pH, and pOH of a 0.1029 M solution of lactic acid. The acid‑dissociation (or ionization) constant, Ka , of this acid is 8.40×10−4." How do you find the percent ionization? I...

Sean Phen

"A monoprotic weak acid, HA , is ionized according to the reaction HA(aq)+H2O(l)↽−−⇀A−(aq)+H3O+(aq)pKa=3.64 where A− is the conjugate base to HA. For this weak monoprotic acid, the predominant species present at pH 2.30 is neutral, unknown, or charged." How do you tell if it is neutral, un...

Sean Phen

How do you determine if a salt is an acid, base, or neutral?

Sean Phen

In some of the problems in Sapling Homework Week 2, I needed to make X negligible. How do you determine if X is supposed to be negligible or not?

Sean Phen

If the Ka of a monoprotic weak acid is 1.6×10−6, what is the pH of a 0.21 M solution of this acid?

I tried solving for the pH, but it always comes out wrong. I am not sure if I am doing the steps correctly. Can someone walk me through it?

Sean Phen

The reaction N2O4↽−−⇀2NO2 is allowed to reach equilibrium in a chloroform solution at 25 ∘C . The equilibrium concentrations are 0.463 mol/L N2O4 and 2.28 mol/L NO2 . Calculate the equilibrium constant, Kc , for this reaction. I was able to get the equation products over reactants, but is it suppose...

Sean Phen

Hi there, What is your question on this topic? Just so you know, you should ask a specific question about a problem, I'm not sure if you get credit for just generally asking for help. I hope this doesn't come off as rude, just letting you know so you can get your points. All the best, Colm Thank yo...

Sean Phen

Consider the reaction at 500°C .

N2(g)+3H2(g)↽−−⇀2NH3(g)Kc=0.061

If analysis shows that the composition of the reaction mixture at 500°C is 1.14 mol⋅ L−1N2 , 5.52 mol⋅ L−1H2 , and 3.42 mol⋅ L−1NH3 , what is the value of the reaction quotient Q?

Sean Phen

At equilibrium, the concentrations in this system were found to be [N2]=[O2]=0.300 M and [NO]=0.400 M. N2(g)+O2(g)↽−−⇀2NO(g) If more NO is added, bringing its concentration to 0.700 M, what will the final concentration of NO be after equilibrium is re‑established? I ended up getting x= -2.16. I am n...

Sean Phen

What are some study strategies for Chem 14B?

Sean Phen

At a certain temperature, the equilibrium constant, Kc, for this reaction is 53.3.

H2(g)+I2(g)↽−−⇀2HI(g)Kc=53.3

At this temperature, 0.600 mol H2 and 0.600 mol I2 were placed in a 1.00 L container to react. What concentration of HI is present at equilibrium?

Sean Phen

At a certain temperature, 0.600 mol SO3 is placed in a 1.50 L container.

2SO3(g)↽−−⇀2SO2(g)+O2(g)

At equilibrium, 0.180 mol O2 is present. Calculate Kc.

Sean Phen

What are the required things to do every week? Is it just chemistry community and the weekly Sapling homework?

Sean Phen

What does the acronym ICE stand for?

Sean Phen

How do you use the ICE method?

Sean Phen

P= Pressure, V= volume, n= number of moles, R= gas constant, and T= temperature

Sean Phen

How do you log in to Sapling homework if you already bought it last quarter? I am unable to log in.

Sean Phen

How do you tell the difference in the lewis structures for mono, bi, tri, and hexa dentate?

Sean Phen

How do you solve for the oxidation state for transition metals?

Sean Phen

How do you tell which is the acid and which is the base?

Sean Phen

How do you solve for the limiting reactant?

Sean Phen

How do you solve for the empirical formula?

Sean Phen

How do you tell if it is a strong or weak acid or base?

Sean Phen

How do you know if a molecule is polar or nonpolar?

Sean Phen

I am not exactly sure about this problem because I did not do it yet. But, there are sometimes more than one way that you can make the Lewis structure.

Sean Phen

The professor does not allow you to see the midterm 2 answers, but the TA does allow you to set up appointments where you can go over the answers with them.

Sean Phen

I believe if you check your email. There is a review session that he is going to do where he will go over previous exams.

Sean Phen

"For each metal complex, give the coordination number for the metal species.
[Co(en)2(CO)2]Br "

How do you figure out the coordination number for this? I tried many times, but I still couldn't figure it out.

Sean Phen

Which geometry or geometries are common for complexes with a coordination number of 6?

Sean Phen

1. Count the number of electron density regions which is 4.
2. You know that s has 1, p has 3, and d has 5. Now, use the number of electron density regions and fill in the hybridizations. So it would come out to sp3.

Sean Phen

I was confused on this question too, but you have to determine the number of electron density regions. Once you know that, you can count the hybridization out. It has four electron density regions, so the hybridization would be sp3.

Sean Phen

Delocalized electrons are electrons that are not associated with only one atom or a covalent bond. Localized electrons display the normal behavior.

Sean Phen

Yes, Lone Pair electrons do count as an electron density region.

Sean Phen

"An organic compound that is distilled from wood has a molar mass of 32.04 g/mol. Its composition by mass is 37.5% carbon, 12.6% hydrogen, and 49.9% oxygen.

Draw the Lewis structure of this compound."

Sean Phen

What is the hybridization of phosphorus in each of the molecules or ions?

Sean Phen

How do you identify the axial and equatorial atoms in a 3-D structure?

Sean Phen

How can you tell if a molecule is dipole-dipole interaction?

Sean Phen

Longer bonds do have a weaker bond, but you also have to consider other factors to determine which boiling point is higher.

Sean Phen

How do you tell which element has a higher melting point?

Sean Phen

For me, I just remember the different patterns for each periodic trend. I remember which periodic trend is going from bottom left to top right, and which are going from top right to bottom left on the periodic table. I also try to understand why each periodic trend is going in that direction due to ...

Sean Phen

N,O, F have high electronegativities, and hydrogen has to bond with elements with high electronegativities. Carbon is not one of them.

Sean Phen

I was also confused on this question as well. I took an educated guess. I saw that it was an ion with a charge so I just added one electron to the expanded valence and got 8 valence electrons. I am not sure if I did it right though.

Sean Phen

How do you classify a species as a Lewis acid or a Lewis base?

Sean Phen

"The observed carbon–oxygen bond lengths in carbamate are both 128 pm, whereas the observed carbon–nitrogen bond length is 136 pm. Expected values are shown in the table. Based on the Lewis structures and the bond length data, select the correct statement or statements." I do not understan...

Sean Phen

"The formulas of the bromate ion, BrO−3, and chlorate ion, ClO−3, are very similar. However, the formulas of the nitrate ion and phosphate ion contain different numbers of oxygen atoms. This is also true for the formulas of the nitrite ion and phosphite ion. Draw the Lewis structures of the nit...

Sean Phen

How can you tell if an atom is either slightly negative or slightly positive? In a lecture, he said, "Atom with closer electron pair is slightly negative while the other covalently bonded becomes slightly positive." I don't understand.

Sean Phen

How do you know which elements are able to have expanded octets?

Sean Phen

Hi, In the lecture #13, the professor was drawing the lewis structure for sulfate, SO4. I am confused how oxygen can form a covalent bond with sulfur when all 6 valence electrons for oxygen are used up in the 3 lone pairs. Where does the extra valence electron come from in order to form a bond with ...

Sean Phen

I did not do too well on midterm 1. Does anyone have any tips for studying for midterm 2?

Sean Phen

I do not know the exact question count for midterm 2. If it is like midterm 1, I definitely believe the professor will give you more than enough time for each question.

Sean Phen

Hi,

I believe this was one of the homework questions from last week (Week 2,3,4 HW). It was Sapling Question #18. If you check out the solution for it, it answers your question thoroughly. Let me know if this helps.

Sean Phen

Hi, the number of elections is equal to the number of protons (in other words: the atomic number).

Sean Phen

I am also a pre-med student, and I am taking bio and chem together. It depends on the person, but I don't think it's a good idea. I am not the best at science.

Sean Phen

I do not know the way to determine electronegativity, but there is a periodic trend for electronegativity which indicates the increasing electronegativity.

Sean Phen

To remember the trends for the periodic table, I would just try looking up diagrams of the periodic table on which way each trend is going. For example, the atomic radius increases in size from the top right to bottom right. In my head, I just try to memorize and picture those diagrams and arrows. T...

Sean Phen

There are periodic trends for determining the size of the atomic radius. If you look at a periodic table, the smallest atomic radius would be in the top right; then, it would increase from top right all the way down to the bottom right of the periodic table. Attached, there is a picture of the perio...

Sean Phen

For this question, I used the Rydberg equation where v=R[(1/n^2)-(1/n^2)]. The first n would be the final energy level (1), and the second n would be the initial energy level (5). After you plug in what you know, you will get v, the frequency. After you get the frequency, you plug it into the speed ...

Search found 121 matches