CHEMISTRY COMMUNITY

Hawa Kamara 1F

Nicola Higgins 14B wrote:I remember TAs and Dr. Lavelle saying that if you ask a question that has already been asked by a different student, it may be deleted. The TAs regularly go through and delete posts that are repetitive to declutter the pages. This may be why your # of posts has decreased!

oooh okay thank you

Hawa Kamara 1F

the reaction

A+B⟶C+Drate=k[A][B]2
has an initial rate of 0.0450 M/s.
What will the initial rate be if [A] is halved and [B] is tripled?

initial rate:
M/s
What will the initial rate be if [A] is tripled and [B] is halved?
initial rate:
how do i go about this?

Hawa Kamara 1F

I would post a few times on chemistry community and my posts would decrease? like when I would post it would be at like 104 posts but then after some time it would go back down to 102.... does this happen for anyone else?

Hawa Kamara 1F

Consider the following reaction at 298 K.

4Al(s)+3O2(g)⟶2Al2O3(s)ΔH =−3351.4 kJ

Calculate the following quantities. Refer to the standard entropy values as needed.

How do I go about this question?

Hawa Kamara 1F

Consider the following reaction at 298 K.

4Al(s)+3O2(g)⟶2Al2O3(s)ΔH =−3351.4 kJ

Calculate the following quantities. Refer to the standard entropy values as needed.

How do I go about this question?

Hawa Kamara 1F

Calculate the standard molar entropy of vaporization of water at 40.0 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 , respectively...

Hawa Kamara 1F

for delta S vap... is the more positive or higher the number does that mean it is more ordered

Hawa Kamara 1F

The molar heat capacity for carbon monoxide at constant volume is CV, m=20.17 J/(K·mol) . A 20.00 -L fixed-volume flask contains CO(g) at a pressure of 9.00 kPa and a temperature of 25.0 C. Assuming that carbon monoxide acts as an ideal gas and that its heat capacity is constant over the given tempe...

Hawa Kamara 1F

The molar heat capacity for carbon monoxide at constant volume is CV, m=20.17 J/(K·mol) . A 20.00 -L fixed-volume flask contains CO(g) at a pressure of 9.00 kPa and a temperature of 25.0 C. Assuming that carbon monoxide acts as an ideal gas and that its heat capacity is constant over the given tempe...

Hawa Kamara 1F

Consider a process in which an ideal gas is compressed to one-sixth of its original volume at constant temperature.

Calculate the entropy change per mole of gas.

What numbers would I plug in?? Do you know?

Hawa Kamara 1F

is it possible foe delta H= positive and ... delta S = negative?

Hawa Kamara 1F

is it possible foe delta H= negative and ... delta S = positive??

Hawa Kamara 1F

How would you explain the difference between enthalpy and entropy ?

Hawa Kamara 1F

A heat source generates heat at a rate of 55.0 W (1 W=1 J/s) . How much entropy does this produce per hour in the surroundings at 27.7 ∘C ? Assume the heat transfer is reversible.

How do I set up this problem?

Hawa Kamara 1F

IsaacLaw1E wrote: $\Delta U = q + w$ , but because volume is constant, w = 0. So really, $\Delta U = q$
$q=nC\Delta T$ , where C is = 3R because SO2 is a non-linear molecule (VSEPR model)
q = (0.461)(3*8.314)(14.9) = 171J, and $\Delta U = q$

is So2 considered linear or nonlinear?

Hawa Kamara 1F

In a problem how do you show or write the constant pressure as well as constant volume?

Hawa Kamara 1F

A constant‑volume calorimeter was calibrated by carrying out a reaction known to release 1.67 kJ of heat in 0.500 L of solution in the calorimeter (q=−1.67 kJ) , resulting in a temperature rise of 3.38 C . In a subsequent experiment, 250.0 mL of 0.20 M HClO2(aq) and 250.0 mL of 0.20 M NaOH(aq) were ...

Hawa Kamara 1F

A 0.201 mol sample of CO2(g), initially at 298 k and 1.00 atm, is held at constant pressure while enough heat is applied to raise the temperature of the gas by 12.1 K. Calculate the amount of heat q required to bring about this temperature change, and find the corresponding total change in the inter...

Hawa Kamara 1F

Michael Crannell 1H wrote:I believe the Correct Cp to use was 3/2R. I remember seeing this problem earlier today when I was studying and using that.

I just realized that they give you the 7R/2 to use. I guess there will be times where they give it to you, because I thought you would use the chart given

Hawa Kamara 1F

okay nvm I figured it out

Hawa Kamara 1F

A 0.201 mol sample of CO2(g), initially at 298 K and 1.00 atm, is held at constant pressure while enough heat is applied to raise the temperature of the gas by 12.1 K. Calculate the amount of heat q required to bring about this temperature change, and find the corresponding total change in the inter...

Hawa Kamara 1F

Why is it when we are doing the change of energy in some problems we don't switch to kelvin and stick with Celsius. Is there a specific reason??

Hawa Kamara 1F

An 80.0 g sample of a gas was heated from 25 C to 225C. During this process, 346 J of work was done by the system and its internal energy increased by 8245 J. What is the specific heat of the gas?

What is "q" within this or how do you calculate "q"?

Hawa Kamara 1F

We are usually given the change of energy in the problems like the exam or do we have to rely on something else? or that just wouldn't happen in general like to memorize

Hawa Kamara 1F

Automobile airbags contain solid sodium azide, NaN3, that reacts to produce nitrogen gas when heated, thus inflating the bag. 2NaN3(s)⟶2Na(s)+3N2(g) Calculate the value of work, w, for the system if 23.8 g NaN3 reacts completely at 1.00 atm and 22 C. In this equation, what is p or how to you find p?

Hawa Kamara 1F

At constant pressure, which of these systems do work on the surroundings?

2A(g)+B(g)⟶4C(g)

A(s)+B(s)⟶C(g)

A(g)+B(g)⟶C(g)

A(s)+2B(g)⟶C(g)

DO you just have to know this off the top of your head or is there s calculation/formula that goes along with this?

Hawa Kamara 1F

nvm I think i was using the wrong numbers...

Hawa Kamara 1F

If you combine 380.0 mL of water at 25.00 ∘C and 130.0 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 thought the anwser was 40.71 C but it keeps saying that it's wrong??? is there somewhere where I am messing up?

Hawa Kamara 1F

When solving the problems mainly for thermochemistry... does it matter when solving the problem is the volume is L vs mL.... when it is an exam what would think is preferred? or it just depends what the problem is asking?? or do we always have to convert to a certain unit regardless of the anwser??

Hawa Kamara 1F

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 when 1.55 mol S8 is reacted at constant pressure. I already solved the first two parts but how would I could about calculating the amount ...

Hawa Kamara 1F

Consider these reactions, where M represents a generic metal. 2M(s)+6HCl(aq)⟶2MCl3(aq)+3H2(g)ΔH1=−918.0 kJ HCl(g)⟶HCl(aq) ΔH2=−74.8 kJ H2(g)+Cl2(g)⟶2HCl(g) ΔH3=−1845.0 kJ MCl3(s)⟶MCl3(aq) Δ4=−272.0 kJ Use the given information to determine the enthalpy of the reaction 2M(s)+3Cl2(g)⟶2MCl3(s) how woul...

Hawa Kamara 1F

Can someone explain the difference in endothermic vs exothermic using the example of like daily things? like baking a cake or ice melting.

Hawa Kamara 1F

I am looking at a sapling question... when you are looking at the compounds how are you able to tell if something is acidic, basic, and neutral? It has something to do with looking at the charge right?

Hawa Kamara 1F

I figured out that you are suppose to use the quadratic equation, but each time I try to solve for the percentage it keeps saying that the answer is wrong. At the end I do the equation of

( dissociated atoms/ the initial amount ) x 100%

Hawa Kamara 1F

The Ka of a monoprotic weak acid is 0.00324. What is the percent ionization of a 0.168 M solution of this acid?

Also how do you set up this type of problem?

Hawa Kamara 1F

why are you always finding the square root in these types of problems? what prompts to finding the square root?

ie... The Ka of a monoprotic weak acid is 0.00324. What is the percent ionization of a 0.168 M solution of this acid?

Hawa Kamara 1F

for the exam will finding the monoprotic weak acid and percentage ionizaion would be a big part of the test or part of a problem?

Hawa Kamara 1F

If the Ka of a monoprotic weak acid is 2.5×10−6, what is the pH of a 0.20 M solution of this acid?

why when you are solving for the pH you square the problem to find the [H]... is [A] count as a ^2??

Hawa Kamara 1F

Are the review sessions recorded? and if so where can i find them?

Hawa Kamara 1F

Consider the reaction of NH3 and I2 to give N2 and HI. 2NH3(g)+3I2(g)↽−−⇀N2(g)+6HI(g) K Using two or more of the given equations, determine the equilibrium constant, K , for the reaction of NH3 with I2. H2(g)+I2(g)↽−−⇀2HI(g) I2(g)↽−−⇀2I(g) N2(g)+3H2(g)↽−−⇀2NH3(g) H2(g)+Cl2(g)↽−−⇀2HCl(g) Ka=160 Kb=2....

Hawa Kamara 1F

I realized that you would only do the b^2-4ac, and not the full quadratic formula... is that correct?

Hawa Kamara 1F

At a certain temperature, the given reaction has an equilibrium constant of Kp=381 .

PCl3(g)+Cl2(g)↽−−⇀PCl5(g)

PCl5 is placed in a sealed container at an initial pressure of 0.0210 bar . What is the total pressure at equilibrium?

I am getting stuck after the ICE table

Hawa Kamara 1F

[This was a reply to one of my questions from before... let me know if you want me to explain more about my question]

so that would mean is the reactant side has a 2[H2]

then it would be .185M -2x or would it just stay as .185M -x?

Hawa Kamara 1F

so that would mean is the reactant side has a 2[H2]

then it would be .185M -2x or would it just stay as .185M -x?

Hawa Kamara 1F

What is the difference between Kp and Kc? Is it a significant difference in the calculation and/or formula?

Hawa Kamara 1F

When you are given just the moles and have to find the Kc, why is that most time after you fine the molarity for the product side.... why is it for instance 0.185M-x .... why are we subtracting the x?

Hawa Kamara 1F

How do you find the Kc, when you are only given the moles of the only reactant, and saying that it is placed in a certain container with a certain amount of liters. Then you are given the moles of one of the products?

Hawa Kamara 1F

What is the number used for the Csp in the equation that you put down?

Hawa Kamara 1F

4J.3 Calculate the change in molar Gibbs free energy for the process at 1 atm and (a) °C (b) °C (see Tables 4C.1 and 4F.1). In each case, indicate whether vaporization would be spontaneous. Can someone explain step by step how to do this problem. I am aware of the formular that we have to use but I ...

Hawa Kamara 1F

how would you do part b in this problem

Hawa Kamara 1F

Did Dr. Lavelle ever mention that he is going to make the tests and midterms worth less if the class average is pretty low?

Hawa Kamara 1F

FOr pi bonds, a triple bond is considered one sigma bond and two pi bonds right?

Hawa Kamara 1F

FOr hydrogen bonds, it can be with any molecule or only with, F,O,N atoms to be considered a chemical bonds?

Hawa Kamara 1F

Is this considered stoichiometry? This topic I mean.

Hawa Kamara 1F

SO basically for naming compounds would it be a huge part of the test? Like would have to name it or being able to know the molecular formula just from the naming of it?

Hawa Kamara 1F

DO we need to bring a calculator to the final?

Hawa Kamara 1F

For longer molecules how are you able to tell what is going to be the central atom and/or what atom is connected to which? for example C5H5NO2.

Hawa Kamara 1F

Thank you for the reply : 3... almost sold my book

Hawa Kamara 1F

Does the VSEPR shape having anything to do with a molecule being polar or nonpolar?

Hawa Kamara 1F

Will we use the same textbook for 14A in 14B?

Hawa Kamara 1F

Will a lewis structure ALWAYS have an even amount of electrons?

Hawa Kamara 1F

Most stable form of a lewis structure usually means that the least amount of lone pairs right?

Hawa Kamara 1F

Is it better to study the past midterm and tests or is it better to do a ton of homework problems?

Hawa Kamara 1F

When determining congratulated bases and acids will water always be part of the chemical equation?

Hawa Kamara 1F

Also, thank you for providing so many hours of help throughout the week for chemistry. It was very helpful and I feel like not many teachers really set aside time for that.

Hawa Kamara 1F

Thank you, Dr. Lavelle, for a fun time in Chemistry.

Hawa Kamara 1F

I am having a hard time trying to figure out the strengths of each of the bonds. Like strongest to weakest.

Hawa Kamara 1F

When doing hybridization is it best to show the charges or each molecule/atom?

Hawa Kamara 1F

Is there going to be a lot of material on the material before the midterm? or like less than newer content.

Hawa Kamara 1F

By any chance would the final be mainly topics on material after the midterm?

Hawa Kamara 1F

Do lone pairs count when figuring out hybridization or not?

Hawa Kamara 1F

Does it matter to show resonance structures when dealing with hybridization on the test or it doesn't matter?

Hawa Kamara 1F

What is the main difference between a lewis acid & base and Bronsted Acid & base?

Hawa Kamara 1F

What is the main difference between a lewis acid & base and Bronsted Acid & base?

Hawa Kamara 1F

What is the main difference between a lewis acid & base and Bronsted Acid & base?

Hawa Kamara 1F

Is what considered a base or acid? Or does it just depends on what the problem is?

Hawa Kamara 1F

Wouldn't the lewis acid be considered an acid the fewer protons and for a lewis base it was be considered a base with more protons right?

Hawa Kamara 1F

What is the difference between ions and a regular atom? How would the electron configuration differ?

Hawa Kamara 1F

When drawing a lewis structure how do you know how many bonds to make between two atoms. Also, how will you be able to determine how many electrons will go on the central atom?

Hawa Kamara 1F

The only way I know to find the limiting reagent is to do the picket fences and see how much of the product is produced from each separate reactant. However, it does get kind of confusing. Is there any other way to find the limiting reagent that is more straight forward/ easier?

Hawa Kamara 1F

To go over my test can I go over it with my T.A. or can I go to a different T.A.? Also, there are some points where I think shouldn't have been taken away.

Hawa Kamara 1F

I think that there are some points on the midterm where I don't think shouldn't have been taken away. Do I have to go to my T.A. or can I go to a different T.A.?

Hawa Kamara 1F

How do you show a lewis structure at it's lowest energy?

Hawa Kamara 1F

Is ionization or electronegativity the same thing, or what makes them different? I believe they have the same trend on the period table.

Hawa Kamara 1F

At any point do we have to name compounds are would the empirical formula be given on the test?

Hawa Kamara 1F

Are we given information to determine how far these bonds i.e single, double, triple; are or do we just have to know in order how far they are like concept wise?

Hawa Kamara 1F

Would the final be cumulative or will we be tested on everything after the midterm?

Hawa Kamara 1F

if the unpaired election is 4pz state. the n=4 would the 'l' be 2?

Hawa Kamara 1F

Double bonds bring the atoms closer together than single bonds. Do I have to explain it using elections or is it the same/ would i get point taken off if I don't use exlectrons in my explanation.

Hawa Kamara 1F

Why is that Oxygen can only have double bonds but in the textbook it can have triple bonds?

Hawa Kamara 1F

Are the contents from test #1 going to be in the midterm?

Hawa Kamara 1F

How many questions are going to be in the midterm?

Hawa Kamara 1F

By any chance would there be a midterm review before the midterm?

Hawa Kamara 1F

What is the significance of 6.626x 10^-34 JS in chemistry

Hawa Kamara 1F

For when getting the theoretical yield, when there will be a time where you don't have to times the equation by 100% (?)

Hawa Kamara 1F

Are there specific compounds we should memorize that will be most commonly seen in this class that we should memorize? Would we have to put two elements together and then name them for a test in the future?

Hawa Kamara 1F

For the lewis structure, do we add more elections when the problem adds a "-(x amount of e)" to the structure regardless of the amount of elections?

Hawa Kamara 1F

Is it alright to apply sig figs at the last calculation or should I start from the very beginning?

Hawa Kamara 1F

Is there any other easy to balance equations? Like some sort of method or short cut?

Hawa Kamara 1F

What sections in the textbook will help study these problems that would be similar to future tests?

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