April 13, 2021, 09:51:49 PM
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91
##### High School Chemistry Forum / Re: Calorimetry Question
« Last post by billyboy on April 09, 2021, 11:37:00 AM »
c= 4.2 j/g*C
deltaT = 31.8*C - 23.5*C
= 8.3*C

mass of HNO3 = 55.0mL/1 x 1g/1mL
= 55.0g

Q= mcDeltaT
= (55.0g)(4.2j/g*C)(8.3*C)
= 1917 x 1kj/1000j
= 1.917kj

n= m/M
= 55.0g/63.02g/mol
= 0.873mol

DeltaH= -Q/n
= -(1.917kj)/0.873mol
= -2.20kj/mol

But the answer should be -54kj/mol
92
##### High School Chemistry Forum / Re: Calorimetry Question
« Last post by Borek on April 09, 2021, 11:18:13 AM »
Show how you got the wrong answer and we will start from there.
93
##### High School Chemistry Forum / Re: Chemistry Hess's Law
« Last post by Borek on April 09, 2021, 11:17:46 AM »
94
##### High School Chemistry Forum / Calorimetry Question
« Last post by billyboy on April 09, 2021, 11:01:27 AM »
Nitric acid reacts with potassium hydroxide as follows:

HNO3 (aq) + KOH(aq) --> KNO3 (aq) + H2O(l)

In an experiment a student placed 55.0 mL of 1.3 mol/L HNO3 and 55.0 mL of 1.3 mol/L KOH into a
calorimeter at 23.5 ̊C. The temperature rose to 31.8 ̊C after the reaction was complete. Calculate the heat
of reaction (∆HR) in kJ/mol of acid. Assume that the specific heat capacity and density of both solutions
are 4.2 J/g ̊C and 1 g/mL respectively.

I've been stuck on this question for a while, I just keep getting the wrong answer.
95
##### High School Chemistry Forum / Chemistry Hess's Law
« Last post by billyboy on April 09, 2021, 10:58:30 AM »
a. Write out the balanced chemical equation for the complete combustion of propene, C3H6 (g).

b. Given the following:

C3H6 (g) + H2 (g) --> C3H8 (g) ∆H ̊R = -124.3 kJ/mol

C3H8 (g) + 5O2 (g) ---> 3CO2 (g) + 4H2O(l) ∆H ̊R = -228.5 kJ/mol

H2 (g) + 1/2O2 (g) ---> H2O(l) ∆H ̊R = -285.5 kJ/mol

Calculate the heat of combustion for propene in kJ/mol.

I did the balancing and I got two different answers: 2C3H6 + 9O2 ---> 6CO2 + 6H2O and C3H6 + 9/2 O2 ---> 3CO2 + 3H2O

My issue comes in when it comes down to forming the equation with the others because every time I look at it the question seems impossible to me.

I also know that the final answer should be -67.3kj/mol which can be done by reversing the last chemical equation but the overall answer would not make sense.
96
##### Organic Chemistry Forum / Re: Stereogenic Center Criteria (Are E-Z Stereoisomers Considered Distinct Groups?)
« Last post by Borek on April 09, 2021, 10:48:43 AM »
97
##### Chemical Engineering Forum / sorbitan ester
« Last post by aggaboyle77 on April 09, 2021, 08:46:52 AM »
Hello,

I am trying to make sorbitan monooleate. I had several pilot reactor trials and unfortunately too muck blacking and carbon formation occured in the reactor. I used phosphoric acid and sodium hydroxide couple as catalyst and the temperature 220 degC under 100 mbar vacuum
Is there another specific catalyst for the production or lower temperature should be applied ?
98
##### Organic Chemistry Forum / Re: Stereogenic Center Criteria (Are E-Z Stereoisomers Considered Distinct Groups?)
« Last post by RH111 on April 09, 2021, 03:53:00 AM »
Thanks for your response. In that case how would I assign priority to those groups (the E-Z stereoisomers) to determine the R-S configuration of the molecule?

~RH111
99
##### Physical Chemistry Forum / Rate Law for Reversible Reaction Without Reaction Mechanism
« Last post by RH111 on April 09, 2021, 03:41:54 AM »
Hi all,

I have been stuck on a chemical kinetics question for quite some time (the question is #26 from the 2021 USNCO local exam).

We are given a reversible reaction A + B  C and are told the forward reaction is kf[A]. We are asked to find the rate law for the reverse reaction.

I think there is not information to identify the reverse rate law because (from what I understand) we know nothing about the reaction mechanism, which is necessary for us to use the steady-state approximation.

My questions are on the following right now:
1. Is the provided information enough for us to identify the reaction mechanism ourselves?
2. Do we even need to know the reaction mechanism to identify the reverse rate? If not, how do I approach this? Is there some theory involved?

Any help is appreciated, thanks!
~RH111
100
##### Undergraduate General Chemistry Forum / Catalyst "supported on polystyrene"
« Last post by Monoamine on April 08, 2021, 08:51:14 PM »
I was reading a synthesis recently, and the authors stated that they used something called PS-BEMP as a catalyst in one of the reaction steps. According to them, this is 2-tert-butylimino-2-
diethylamino-1,3-dimethylperhydro-1,3,2-diazaphosphorine supported on polystyrene , which they claim is a very strong base.
I understand the "using a base as a catalyst" part, but I don't know what "supported on polystyrene" means?

Is the above chemical somehow attached to pieces of polystyrene, which are then placed into the reaction vessel? And if so, how is this usually done? (I'm pretty sure they don't mean take a piece of polystyrene, lather it in super glue and then dip it in the base...)

FYI: I saw this in the following paper about Henry syntheses:
Angelini T, Ballerini E, Bonollo S, Curini M, Lanari D. A new sustainable protocol for the synthesis of nitroaldol derivatives via Henry reaction under solvent-free conditions. Green Chemistry Letters and Reviews. 2014 Jan 2;7(1):11-7

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