CHEMISTRY COMMUNITY

Jessica Luong 3K

What is a rate determining step? How would we know?

Jessica Luong 3K

Can anyone please explain why an endothermic reaction would have a higher activation energy than the reverse reaction?

Jessica Luong 3K

Can someone explain to me the difference between an activation complex and a transition state?

Jessica Luong 3K

A particular reactant decomposes with a half‑life of 167 s when its initial concentration is 0.318 M. The same reactant decomposes with a half‑life of 227 s when its initial concentration is 0.234 M. I know that I will be using the second order half-life equation to find K, but for some reason, I ke...

Jessica Luong 3K

The presence of a catalyst provides a reaction pathway in which the activation energy of a reaction is reduced by 74.00 kJ⋅mol−1. Uncatalyzed: A⟶B Ea=139.00 kJ⋅mol−1 Catalyzed: A⟶B Ea=65.00 kJ⋅mol−1 Determine the factor by which the catalyzed reaction is faster than the uncatalyzed reaction at 286.0...

Jessica Luong 3K

I was able to figure out the half-life for this problem, but I am not sure which equation and how to solve it for the next two questions. Dinitrogen pentoxide, N2O5, decomposes by first‑order kinetics with a rate constant of 3.7×10−5 s−1 at 298 K. What is the half‑life, in hours, of N2O5 at 298 K? -...

Jessica Luong 3K

The rate constant for this zero‑order reaction is 0.0110 M·s−1 at 300 ∘C.
A⟶products
How long (in seconds) would it take for the concentration of A to decrease from 0.900 M to 0.330 M?

For this question, which equation should I use?

Jessica Luong 3K

I'm having trouble understanding the concept to solve this question. Can someone simplify an explanation for me?

Jessica Luong 3K

For question 4, can someone help me identify the proper units? I don't know which ones I got right and which ones I got wrong :(

Jessica Luong 3K

How would I find the rate of A? In the feedback, it was mentioned that I needed to find A before I could find out the rate of B. Can someone help me with this?

Jessica Luong 3K

Calculate the cell potential for the reaction as written at 25.00 °C , given that [Mg2+]=0.891 M and [Fe2+]=0.0100 M . Use the standard reduction potentials in this table. Mg(s)+Fe2+(aq)↽−−⇀ Mg2+(aq)+Fe(s) Can someone help me figure out step by step what I should do? I know that I need to find the s...

Jessica Luong 3K

Calculate the standard free-energy change for the reaction at 25 ∘C. Refer to the list of standard reduction potentials. 2Au3+(aq)+3Cr(s)↽−−⇀2Au(s)+3Cr2+(aq) For this question, I know that I should use deltaG = -nFE. Before that, I should calculate E by using the standard reduction potentials chart....

Jessica Luong 3K

Separate this redox reaction into its balanced component half‑reactions. Use the symbol e− for an electron. Cl2+2Na⟶2NaCl I was able to figure out the oxidation half-reaction which was 2Na --> 2(Na+) + 2e-. However, I am having a problem figuring out the correct reduction half-reaction. From my calc...

Jessica Luong 3K

For this question, I keep getting the feedback "the cathode should occupy the right-hand position of the line diagram." However, the boxes I filled into the shorthand notation were from the cathode half-reaction. Can someone give me a few pointers on what I'm doing wrong?

Jessica Luong 3K

I have trouble with the understanding of cation and anion flow within a galvanic cell. Also, for the salt bridge, which way would the cations and anions flow through it?

Jessica Luong 3K

Identify the oxidizing and reducing agents in the skeletal (unbalanced) reaction. Then, balance the reaction, including the phase (solid, liquid, etc.) of each species. The reaction takes place in basic aqueous solution. Cl2O7(g)+H2O2(aq)⟶ClO−2(aq)+O2(g) I'm having a problem balancing this equation ...

Jessica Luong 3K

For #18, I have to find the equilibrium constant K using the deltaG(f) equation. I followed all of the instructions where you find the deltaG and then use the equation deltaG = -RT*ln(K). However, I keep getting the wrong answer. Can someone help me with the steps to solve this problem?

Jessica Luong 3K

I know how to solve for #7, but what I'm confused about is why are we subtracting the final mass from the initial mass instead of vice versa? Don't we usually do Tfinal - Tinitial to find the mass difference? What is it Tinitial - Tfinal for this question?

Jessica Luong 3K

"A particular container holds 3.24 mol of neon gas. The volume of this container can be altered by sliding a piston in or out. The volume is changed from 8.60 L to 3.70 L while at the same time the temperature is changed from 333 K to 233 K. The molar heat capacity, CV,m, for neon is 12.47 J/(m...

Jessica Luong 3K

Is there any easy way to figure out which phase changes is occurring by just using the signs of delta H and delta S? Which one should I look at when answering these type of questions, like #3 on Sapling?

Jessica Luong 3K

"A heat source generates heat at a rate of 83.0 W (1 W=1 J/s) . How much entropy does this produce per hour in the surroundings at 27.6 ∘C ? Assume the heat transfer is reversible." I have already converted the temperature and the watts to Joules per hour, but I am still getting the wrong ...

Jessica Luong 3K

A constant‑volume calorimeter was calibrated by carrying out a reaction known to release 2.03 kJ of heat in 0.800 L of solution in the calorimeter (q=−2.03 kJ) , resulting in a temperature rise of 3.18 C . In a subsequent experiment, 400.0 mL of 0.40 M HClO2(aq) and 400.0 mL of 0.40 M NaOH(aq) were ...

Jessica Luong 3K

to find the moles you have to use PV=nRT and solve for n, then plug that back in to the equation w=-nRTln(v2/v1) and make sure that you use 0.0821 L*atm/mol*K for R in the first part and 8.314 J/K*mol for R in the second part Hey! Thank you for the reply. Why do we know when to use 0.0821 and when ...

Jessica Luong 3K

For #14, I know I am suppose to start with the w = -nRT*ln(v2/v1), but I don't know how to find moles or n in order to solve this problem. I am also having a hard time understanding which equation and how to solve for the second part. A sample of an ideal gas in a cylinder of volume 3.65 L at 298 K ...

Jessica Luong 3K

For Sapling HW #12, why is compound A denoted as a positive answer, but compound B is denoted with a negative answer? I'm not quite understanding the concept behind this. Can someone explain to me why this is?

Jessica Luong 3K

I can't seem to solve this question. Can someone help me detail the steps on how to solve this? A hot lump of 27.6 g of iron at an initial temperature of 94.7 °C is placed in 50.0 mL H2O initially at 25.0 °C and allowed to reach thermal equilibrium. What is the final temperature of the iron and wate...

Jessica Luong 3K

In Friday’s lecture, can someone explain to me how the heat reservoir, when it’s slowly decreasing external pressure and loses heat (energy), that it’s still at pressure and thermal equilibrium? I don't quite get how this example works.

Jessica Luong 3K

In lecture, why is the H+ (aq) + OH- (aq) —> H2O (l) important? How did Dr.Lavelle use this reaction to figure out that the neutralization is exothermic?

Jessica Luong 3K

Can someone dumb down the explanation as to why gases need to have their condition specified and not solids or liquids?

Jessica Luong 3K

Can someone explain to me how to solve #9 on Sapling for Week 3 and 4? I can't seem to get the right answer.

Jessica Luong 3K

I am a bit confused on which expressions are endothermic and exothermic. How would we identify them? I thought that we just needed to see whether or not the bonds are strong or weak? For example, with stronger bonds they require more energy or heat to break the bonds so it is endothermic? However, I...

Jessica Luong 3K

For method 3, how would we solve the problem if the reactants are a liquid or a solid? In lecture, we only went over the example which already had everything in standard state. Therefore, I was wondering what the process would look like if we had to include the enthalpy of vaporization into our calc...

Jessica Luong 3K

Will we always be given the standard enthalpy for the elements/compounds for exams? If not, are we suppose to look them up during the exam or be able to print out the chart beforehand?

Jessica Luong 3K

Can someone explain to me how we would know that there are two steps that need to be done in order to change Br2 (liquid) to Br2 (gas) and then to 2 Br (gas)? This is the example Dr. Lavelle was explaining in Friday's lecture under the additional comments explaining about the bond enthalpies.

Jessica Luong 3K

Does pKa = pH? Is this relationship situational or always constant?

Jessica Luong 3K

I am confused as to why the we do not include Na from NaClO in the ice table if we included H in HClO. Both Na and H are in group 1 so why can we use one but not the other?

Jessica Luong 3K

Hey! Can someone help explain to me the steps on how to solve #5 on Sapling for the Week 2 Homework? The question is: The Kb for an amine is 1.243×10−5. What percentage of the amine is protonated if the pH of a solution of the amine is 9.062 ? Assume that all OH− came from the reaction of B with H2O...

Jessica Luong 3K

For % ionization and checking to see whether or not our assumption was correct, do we solve it the same way? Is it x at equilibrium divided by x initial molar concentration?

Jessica Luong 3K

Can someone re-explain to me the section about when to use 10^-7 for [H3O+] instead of the initial molar concentration? I didn’t quite understand Lavelle in Friday’s lecture when we were calculating the pH of weak acids and bases in the “Notes.” If [H3O+] was less than 10^-7 then wouldn’t it be acid...

Jessica Luong 3K

What do I do when there is a coefficient in front of the products when solving for the equilibrium constant?

Jessica Luong 3K

Is the enthalpy directly related to whether or not the reaction is endothermic or exothermic? For example, if enthalpy is positive then the reaction is always endothermic.

Jessica Luong 3K

Does anyone have any mnemonics to remember the Q and K relationship better?

Jessica Luong 3K

Can someone explain to me how to solve for the equilibrium constant for Question 2 on Sapling? I can't seem to get the right answer for this question.

Jessica Luong 3K

I was wondering if it matters whether or not we solve for the concentrations at the beginning during ICE tables or later on at the end. Would solving for the concentration at the end affect the results?

Jessica Luong 3K

Estimate the bond angles marked with arcs and lowercase letters in peroxyacetylnitrate, an eye irritant in smog: Peroxyacetylnitrate

Jessica Luong 3K

Methane, the most abundant hydrocarbon in the atmo- sphere and a potent greenhouse gas, is slowly oxidized in the air to carbon dioxide. An intermediate in the oxidation of methane to carbon dioxide is HOCO. (a) Draw the Lewis structure for this compound. (b) Decide whether the compound is a radical.

Jessica Luong 3K

Acetonitrile, CH3CN, is used as a solvent in the pharmaceu- tical industry. Describe the structure of the CH3CN molecule in terms of hybrid orbitals, bond angles, and s- and p-bonds. The N atom is a terminal atom.

Jessica Luong 3K

Consider the bonding in H2CPCHCHO. (a) Draw the most important Lewis structure. Include all nonzero formal charges. (b) Identify the composition of the bonds and the hybridization of each lone pair—for example, by writing s(H1s,C2sp2).

Jessica Luong 3K

(a) Draw a Lewis structure for each of the following species: CH31; CH4; CH32; CH2; CH221; CH222. (b) Identify each as a radical or not. (c) Rank them in order of increasing HCH bond angles. Explain your choices.

Jessica Luong 3K

Describe the structure of the formaldehyde molecule, CH2O, in terms of hybrid orbitals, bond angles, and s- and p-bonds. The C atom is the central atom to which the other three atoms are attached.

Jessica Luong 3K

Noting that the bond angle of an sp3 hybridized atom is 109.58 and that of an sp2 hybridized atom is 1208, do you expect the bond angle between two hybrid orbitals to increase or decrease as the s-character of the hybrids is increased?

Jessica Luong 3K

Acrylonitrile, CH CHCN, is used in the synthesis of 2
acrylic fibers (polyacrylonitriles), such as Orlon. Draw the Lewis structure of acrylonitrile and describe the hybrid orbitals on each carbon atom. What are the approximate values of the bond angles?

Jessica Luong 3K

Identify the hybrid orbitals used by the phosphorus atom in each of the following species: (a) PCl41; (b) PCl62; (c) PCl5; (d) PCl3.

Jessica Luong 3K

Identify the hybrid orbitals used by the atom in boldface red type in each of the following species: (a) BF3; (b) AsF3; (c) BrF3; (d) SeF31.

Jessica Luong 3K

State the hybridization of the atom in boldface red type in each of the following molecules and ions: (a) BeCl2; (b) BH3; (c) BH42; (d) SiF4.

Jessica Luong 3K

How many s-bonds and how many p-bonds are there in (a) H2S and (b) SO2?

Jessica Luong 3K

There are three isomers of dichlorobenzene, C6H4Cl2, which differ in the relative positions of the chlorine atoms on the benzene ring. (a) Which of the three forms are polar? (b) Which has the largest dipole moment?

Jessica Luong 3K

Predict whether each of the following molecules is likely to be polar or nonpolar: (a) C5H5N (pyridine, a molecule like benzene except that one OCHO group is replaced by a nitrogen atom); (b) C2H6 (ethane); (c) CHCl3 (trichloromethane, also known as chloroform, a common organic solvent and once used...

Jessica Luong 3K

Draw the Lewis structure and predict whether each of the following molecules is polar or nonpolar: (a) CH2Cl2; (b) CCl4; (c) CS2; (d) SF4.

Jessica Luong 3K

Draw the Lewis structure and predict the shape of (a) OSbCl3; (b) SO2Cl2; (c) IO2F22. The atom in boldface red type is the central atom.

Jessica Luong 3K

What are T-shapes?

Jessica Luong 3K

What are interionic and intermolecular attractive forces?

Jessica Luong 3K

What is isoelectronic?

Jessica Luong 3K

Are there any other trends besides electron affinity, ionization, and electronegativity?

Jessica Luong 3K

How do you find the 4th quantum number?

Jessica Luong 3K

What is a coordinate covalent bond?

Jessica Luong 3K

Which M31 ions (where M is a metal) are predicted to have the following ground-state electron configurations: (a) [Ar]3d6; (b) [Ar]3d5; (c) [Kr]4d5; (d) [Kr]4d3?

Jessica Luong 3K

Write the ground-state electron configuration for each of the following atoms: (a) sodium; (b) silicon; (c) chlorine; (d) rubidium.

Jessica Luong 3K

Of the following sets of four quantum numbers {n,l,ml,ms}, identify the ones that are forbidden for an electron in an atom and explain why they are invalid:
(a) {54,2,21,16}; (b) {55,0,21,16}; (c) {54,4,21,16}.

Jessica Luong 3K

Write the subshell notation (3d, for instance) and the number of orbitals having the following quantum numbers: (a) n 5 5, l52; (b) n51,l50;(c) n56,l53; (d) n52,l51.

Jessica Luong 3K

For each orbital listed in Exercise 1D.15, give the possible values of the magnetic quantum number.

Jessica Luong 3K

Can someone help me break down electron configuration and explain what it is?

Jessica Luong 3K

Hi, can someone re-explain to me the "stern and gerlach experiment: electron spin" from class? I didn't quite understand the concept.

Jessica Luong 3K

Why do we have to know about the nodal planes? What's their relevance to the orbitals?

Jessica Luong 3K

What does schrodinger's equation look like?

Jessica Luong 3K

What's the importance of the orbitals? Why do we need to know this?

Jessica Luong 3K

What is spectroscopic analysis? What do we use this for?

Jessica Luong 3K

In what situations do you use De Broglie's equation, Heisenberg's equation, and Schrodinger's equation?

Jessica Luong 3K

In what equation do we use Kydberg's Constant, 3.29 x 10^15?

Jessica Luong 3K

What is "h" in the equations we have been using? It's the one with the same numbers, 6.626 x 10^-34 Js.

Jessica Luong 3K

Can someone re-explain to me what a threshold energy is? What do we need to know this for? Thank you!

Jessica Luong 3K

Omg thank you so much! This chart and the naming iconic compound video is really helpful!!

Jessica Luong 3K

When balancing equations, make sure you start with the element with the least amount of atoms. In this case, it should be Mg. However, both sides of the equation have exactly 1 Mg, so you didn't need to do anything. Next, you should look at N. There are 6 N atoms on the left side and 3 on the right ...

Jessica Luong 3K

What other prefixes/suffixes should I be aware of when naming compounds? The only ones I've seen so far were di-, -ate, and -ite. If there are more, please reply below because I don't wanna bomb my first test.

Jessica Luong 3K

What's the significance of an ion's charge when writing compound formulas? Why is it relevant to know whether or not the charge is positive or negative? Also, do you guys know if these will be on the test?

Jessica Luong 3K

Does anyone have any easy tips/tricks to memorizing the polyatomic ions?

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