CHEMISTRY COMMUNITY

Hena Sihota 1L

The ochem Dr Lavelle went over in lecture today will be on the final. He recently posted on chem community that "identifying functional groups given the structure" will be on the final and that he will go through more examples during lecture on Wednesday.

Hena Sihota 1L

Just like the midterm, the final will have 8 questions, but these questions will most likely have several parts and take longer to solve when compared to the questions on the midterm. However, you should have plenty of time to finish, since we'll have one more hour than we had for the midterm.

Hena Sihota 1L

Yes, I believe so.

Hena Sihota 1L

This problems asks you to rank the following in order of increasing reducing power: a)Zn, Mn, Cr b)I 2 , Br 2 , Al I understood that the more negative the reduction potential, the greater the reducing power, and applied this logic to both parts. I wrote out the reduction potentials and ordered them ...

Hena Sihota 1L

What is the correct answer for this question: Calculate the standard potential for the following reaction using the standard reduction potentials on the last page of the test: Cr₂O₇^2-(aq)+14H⁺(aq)+12e^-->2Cr(s)+7H₂O(l)

Hena Sihota 1L

I think Lyndon will give us a packet of problems on electrochemistry and kinetics similar to the practice midterm he gave us that covered thermochemistry and thermodynamics, so if you combine these two packets it's almost like a long practice final. I think he's focusing on electrochemistry and kine...

Hena Sihota 1L

Additionally, example 15.2 in the textbook explains how to find the order of the reactants and the order of the overall reaction if you're given a table of experimental data.

Hena Sihota 1L

ln[A]t-ln[A]0=-kt If you divide both sides of this equation by -1 then you get -[A]t+[A]0=kt which can be rewritten as [A]0-[A]t=kt. According to log rules, this equation can be rewritten as ln[A]0/ln[A]t=kt

Hena Sihota 1L

The equations ln[A] 0 /ln[A] t =kt and ln[A] t -ln[A] 0 =-kt are equivalent. If you divide both sides of the second equation by -1 then you get -[A] t +[A] 0 =kt which can be rewritten as [A] 0 -[A] t =kt. According to log rules, this equation can be rewritten as ln[A] 0 /ln[A] t =kt which is the fi...

Hena Sihota 1L

I believe that "n" is just the number of moles.

Hena Sihota 1L

Part B asks you to determine the rate of formation for O₂. The solutions manual gives the units in (mol O₂).L^-1.s^-1. Is it wrong to leave the O₂ out of the units and just leave it as mol.L^-1.s^-1?

Hena Sihota 1L

units for k₀: mol.L^-1.s^-1
units for k₁: s^-1
units for k₂: L.mol^-1.s^-1

Hena Sihota 1L

These three terms are related by deltaS_total=deltaS_system+deltaS_surroundings.

Hena Sihota 1L

Hi! I have the same question, because sometimes the solutions manual and TAs add 273 instead of 273.15 when converting from Celsius to Kelvin and I've noticed that the answers are slightly different. However, since the equations sheet that we get for the midterm has "0 degrees Celsius=273.15 K&...

Hena Sihota 1L

Question 7 on Test 1: In order to make iced-tea, a 50.0 g ice cube at 0.0 degrees Celsius is added to 250mL of tea at 20.0 degrees Celsius. What is the final temperature of the iced-tea once it has reached thermal equilibrium? Assume no heat is transferred to or from the surroundings. I solved it us...

Hena Sihota 1L

All of the material covered up until Friday, February 2 (chapters 8, 9, and 11) will be on the midterm.

Hena Sihota 1L

No, this class is not Bruincasted.

Hena Sihota 1L

The midterm will cover material from chapters 8, 9, and 11, so do the assigned homework problems for those chapters. Chapter 14 (electrochemistry) will not be on the midterm.

Hena Sihota 1L

Non-spontaneous processes can be done by both work and heat.

Hena Sihota 1L

According to the syllabus, you should read sections 3, 11, 12, and 13 of chapter 11. I believe that we are also responsible for knowing the rest of chapter 11, which was covered in chem 14A.

Hena Sihota 1L

The textbook defines Gibbs free energy as the energy of a system that is free to do work at constant temperature and pressure. The direction of spontaneous change at constant pressure and temperature is the direction of decreasing Gibbs free energy.

Hena Sihota 1L

Professor Lavelle sent an email a while ago that said we can pick up our fall quarter final during week 3 from 4006 Young Hall.

Hena Sihota 1L

The problem states that the reaction produces hydrogen gas and chloride ions , so the chemical equation can be rewritten as 2HCl (aq) +Zn (s) -->H 2(g) +Zn 2+ (aq) +2Cl - (aq) . You can now find all the enthalpies of formation needed to find the enthalpy of th...

Hena Sihota 1L

I have Mackenzie as a TA, and last week during discussion she didn't specify whether she wanted HW problems from chapter 8 or chapter 9 for week 3. On another chemistry community post Dr Lavelle commented that we can turn in any 7 problems from chapter 8 for week 3 HW, so that's what I'm doing, but ...

Hena Sihota 1L

The following equation was given in lecture today: DeltaU=energy transferred by heating (+q) + energy transferred by compression (+w) If the system was cooled instead of heated you would just replace "heating (+q)" with "cooling (-q)" and if the system was expanded instead of com...

Hena Sihota 1L

I was looking back through my notes and I was confused by one of the answers given to an example in lecture. Professor Lavelle went over the example "98 kJ of heat are required to raise the temperature of some ethanol by 2 degrees Celsius. What is the heat capacity for this ethanol?", and ...

Hena Sihota 1L

I'm pretty sure that we don't need to know how to derive the formulas we learned. I believe that Professor Lavelle just shows us the derivations so that we have a better understanding of where the formulas we use come from and how the formulas we use are related to one another, which is helpful when...

Hena Sihota 1L

C-solid (graphite), I,Br-liquid, N,O,F,Cl-gas
I believe that these are correct.

Hena Sihota 1L

I don't believe that we will have to commit any of them to memory. We've been talking about them for 2 lectures and Professor Lavelle hasn't mentioned that we have to memorize them, but I'm not 100% positive.

Hena Sihota 1L

I would say a fish tank is a closed system.

Hena Sihota 1L

Number 7 asks: From number 1, SO 3(g) <-->SO 2(g) +O 2(g) . The K c of the reverse reaction is 5.66*10^(-10). What are the equilibrium concentrations of all the products and reactants if you first introduce a 0.522M sample of SO 2 with a 0.633M sample of O 2 ? I have 2 questi...

Hena Sihota 1L

Number 8 asks: Will the equilibrium constant K increase, decrease, or remain constant after the following changes to the exothermic reaction 4A (g) +3B (g) <-->2C (g) Part C States: The stoichiometric coefficients are doubled _________ Lyndon's answer key says that "eith...

Hena Sihota 1L

You would increase the yield of ammonia by removing the ammonia as it is produced in the reaction. By constantly removing the product you would prevent the reaction from reaching equilibrium and since there would then be far more reactants than products, the forward reaction would be strongly favore...

Hena Sihota 1L

@RobertEstrada At equilibrium the concentrations of the reactants and products remain constant. From flask 1 to 2 and from flask 2 to 3 the concentrations of the reactant and product change. However, from flask 3 to 4 the concentrations of the reactant and product remain the same; therefore, you kno...

Hena Sihota 1L

By "the opposite side of the equation" do you mean the reverse reaction? If so, yes. If you have the value of the equilibrium constant for the forward reaction, you can calculate the value of the equilibrium constant for the reverse reaction by taking the reciprocal of the equilibrium cons...

Hena Sihota 1L

It means that the reactants are forming the products at the same rate that the products are creating the reactants.

Hena Sihota 1L

Yes, you are correct.

Hena Sihota 1L

This occurs when there is sp or sp^2. For sp only one of the 3 p orbitals is hybridized along with the 1 s orbital. Therefore, there are 2 sp hybridized orbitals and 2 unhybridized p orbitals. The same goes for sp^2 except 2 of the p orbitals are hybridized along with the 1 s orbital and 1 of the p ...

Hena Sihota 1L

So I don't use the 1.5 anywhere?

Hena Sihota 1L

How do you solve this problem? A professor is walking towards the class. An electron in his body has a speed of 1.5 +/- 0.4 m/s. What is the uncertainty in the position of the electron? I got deltax= (1.05457x10^(-34))/(2x(9.1095x10^(-31))x(2.3))= 2.5x10^(-5) m, but the correct answer is 7.35x10^(-5...

Hena Sihota 1L

How would you solve this problem:
The following two-step reaction produces hydrogen.
Step 1: CH₄+H₂O->CO+3H₂
Step 2: CO+H₂O->CO₂+H₂
Given 0.036g of methane (CH₄) and 0.108g of water, how much hydrogen, in grams, is produced?

Hena Sihota 1L

Yes, the terms "angular" and "bent" can be used interchangeably; they mean the same thing.

Hena Sihota 1L

@leilawilliams16 You don't always have to calculate the formal charge after drawing a lewis structure, because formal charge is only used to determine the most stable structure when molecules or ions have resonance, and therefore resonance structures. For example, CH 4 does not have resonance, so yo...

Hena Sihota 1L

Effective nuclear charge is the net nuclear charge after taking into account the shielding caused by other electrons in the atom. Nuclear charge and shielding are related by the equation Z(eff)=Z-S, where Z(eff) is the effective nuclear charge, Z is the atomic number, and S is the number of shieldin...

Hena Sihota 1L

Ionization refers to the conversion of atoms or molecules into ions by the transfer of electrons. Ionization energy is the minimum energy required to remove an electron from the ground state of a gaseous atom, molecule, or ion.

Hena Sihota 1L

The textbook defines diagonal relationships as "a similarity in properties between diagonal neighbors in the main groups of the periodic table," so yes we only see diagonal relationships in main group elements.

Hena Sihota 1L

Problem #7: A) An electron was ejected from the surface of an unknown metal. The ejected electron had 2.35 x 10^(-18) J of kinetic energy. The photon used to eject the electron had 4.19 x 10^(-18) J of energy. Calculate the work function (or threshold energy) of the unknown metal. B) What is the vel...

Hena Sihota 1L

For problem 1.23 I calculated the wavelength in nm, but when I went to check my answer with the solutions manual it had the answer in pm. How do I know which units to use for the final answer when calculating wavelength?

Hena Sihota 1L

When using the Rydberg formula to calculate the frequency and you get a negative value do you omit the negative sign for the final answer because frequency can't be negative? Or do you leave the negative sign because it indicates that the electron went from a higher energy level to a lower energy le...

Hena Sihota 1L

When asked to calculate the molecular formula of a compound (for this example: Compound C which is comprised of the elements A and B) and you're given the grams of C produced, the molar mass of C, the grams of A, and the grams of B, is there a faster way to calculate the molecular formula of C other...

Hena Sihota 1L

The delta symbol above the arrow in a chemical equation simply indicates that in order for the reaction to take place heat must be applied to the reactants. The delta symbol does not affect how you balance the chemical equation.

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