It is currently Sat Aug 19, 2017 3:47 am

 22 posts • Page 1 of 1
Author Message
M_Gabriela
 Post subject: chemistry problem  |  Posted: Thu Mar 02, 2017 4:35 pm

Joined: Tue May 03, 2016 2:25 pm
Posts: 217
Location: Bs As, Argentina

 Hello, I have this problemH30+ + 2 NO2- + 2 I- --> I2 + 2 NO + 6 H2OThe problem asks for the order of reaction with respect to I2, the product. How do I do that? Then it asks the reaction rate if formation rate of NO is xx M/s...I have more data... For example for the first question I need to find the concentration of H30+ and I have the reaction rate, the k, and the concentration of NO2 and I-. And the expression of the reaction rate so I only have to clear H30+.But then it asks me to find a new reaction rate if NO formation rate is xx M/s... I'm lost....Thankss in advance
PhDemon
 Post subject: Re: chemistry problem  |  Posted: Thu Mar 02, 2017 5:36 pm

Joined: Wed Jun 26, 2013 10:44 am
Posts: 497
Location: Newcastle-upon-Tyne

 Could you post the whole question with the data (maybe as an image)? It might be clearer to me then how you go about solving it.Asking for a reaction order WRT to a product seems a little odd...Also your equation as written doesn't look correct, the charges don't balance... _________________"The big trouble with dumb bastards is that they are too dumb to believe there is such a thing as being smart"- Kurt Vonnegut, The Sirens of Titan
M_Gabriela
 Post subject: Re: chemistry problem  |  Posted: Thu Mar 02, 2017 5:57 pm

Joined: Tue May 03, 2016 2:25 pm
Posts: 217
Location: Bs As, Argentina

 It's in spanish .Yes, the equation is wrong.4 H30+ + 2 NO2- + 2 I- --> I2 + 2 NO + 6 H2OThe reaction rate isv= k x [NO2 -] x [I -] x [H3O+]^21) Value of H3O+ if... and they give me all the data to clear H30+ from the equation above.2) order of reaction with respect to I2.3)Value of reaction rate when formation rate of NO is xxxxx M/s.
PhDemon
 Post subject: Re: chemistry problem  |  Posted: Thu Mar 02, 2017 6:05 pm

Joined: Wed Jun 26, 2013 10:44 am
Posts: 497
Location: Newcastle-upon-Tyne

 OK, I guess you've done part one (the easy bit :p)...As for part two I2 does not appear in the rate equation and has no effect on the rate so the order with respect to it must be zero (although I still think it strange asking about a product in this way, I've never seen that before unless it's an equilibrium).Part 3, "v" in your equation is equal to $\displaystyle \frac{1}{2} \frac{d[NO_2]}{dt}$ and this is the reaction rate, so the rate of reaction is half of your xxxx M/s _________________"The big trouble with dumb bastards is that they are too dumb to believe there is such a thing as being smart"- Kurt Vonnegut, The Sirens of Titan
M_Gabriela
 Post subject: Re: chemistry problem  |  Posted: Thu Mar 02, 2017 6:25 pm

Joined: Tue May 03, 2016 2:25 pm
Posts: 217
Location: Bs As, Argentina

 PhDemon wrote:OK, I guess you've done part one (the easy bit :p)...As for part two I2 does not appear in the rate equation and has no effect on the rate so the order with respect to it must be zero (although I still think it strange asking about a product in this way, I've never seen that before unless it's an equilibrium).Part 3, "v" in your equation is equal to $\displaystyle \frac{1}{2} \frac{d[NO_2]}{dt}$ and this is the reaction rate, so the rate of reaction is half of your xxxx M/sThanksss. A few questionsAbout part 3, so you're saying that the difference between reaction rate and formation rate is only the 1/2???Cause I thought that formation rate was $\displaystyle \frac{1}{2} \frac{d[NO_2]}{dt}$. So I would have to multiply by 2 if I want to clear the $\displaystyle {d[NO_2]}/{dt}$I feel like I'm writing something really stupid....About part 2. I only read about order of reaction respect to reactants, not products, that's why I was lost. again thank you!
PhDemon
 Post subject: Re: chemistry problem  |  Posted: Thu Mar 02, 2017 6:29 pm

Joined: Wed Jun 26, 2013 10:44 am
Posts: 497
Location: Newcastle-upon-Tyne

 The rate of reaction (v in your equation) can be expressed in terms of any of the reactants or products as: $\displaystyle \frac{1}{n} \frac{d[X]}{dt}$ where n is the stoichiometric coefficient in front of X... This should give the same value for the rate regardless of which reactant or product you use. _________________"The big trouble with dumb bastards is that they are too dumb to believe there is such a thing as being smart"- Kurt Vonnegut, The Sirens of Titan Last edited by PhDemon on Thu Mar 02, 2017 6:34 pm, edited 3 times in total.
M_Gabriela
 Post subject: Re: chemistry problem  |  Posted: Thu Mar 02, 2017 6:31 pm

Joined: Tue May 03, 2016 2:25 pm
Posts: 217
Location: Bs As, Argentina

 And what is this:v= k x [NO2 -] x [I -] x [H3O+]^2???
PhDemon
 Post subject: Re: chemistry problem  |  Posted: Thu Mar 02, 2017 6:33 pm

Joined: Wed Jun 26, 2013 10:44 am
Posts: 497
Location: Newcastle-upon-Tyne

 That is the rate law. It tells you how the rate depends on the concentration of each reactant. _________________"The big trouble with dumb bastards is that they are too dumb to believe there is such a thing as being smart"- Kurt Vonnegut, The Sirens of Titan
M_Gabriela
 Post subject: Re: chemistry problem  |  Posted: Thu Mar 02, 2017 6:44 pm

Joined: Tue May 03, 2016 2:25 pm
Posts: 217
Location: Bs As, Argentina

 Ok... I don't understand why I have to divide by 2. I understand where the 1/2 comes from but I don't understand why, to calculate the reaction rate, I have to do that.$\displaystyle \frac{1}{2} \frac{d[NO_2]}{dt}$ = vif v= xxxx M/s, then$\displaystyle \frac{1}{2} \frac{d[NO_2]}{dt}$ = xxxx M/sso why divide it?
PhDemon
 Post subject: Re: chemistry problem  |  Posted: Thu Mar 02, 2017 6:58 pm

Joined: Wed Jun 26, 2013 10:44 am
Posts: 497
Location: Newcastle-upon-Tyne

 You are given the rate of formation of NO, not the "rate of the reaction". The reaction rate is defined in my above post, you need to use that 1/n bit. If you didn't you would get a different answer for the rate depending on which reactant ir product you chose to measure the concentration change of...Edit: the NO2 in my equations above should be NO, does that clear up your confusion? (It's been a long day! ) _________________"The big trouble with dumb bastards is that they are too dumb to believe there is such a thing as being smart"- Kurt Vonnegut, The Sirens of Titan Last edited by PhDemon on Thu Mar 02, 2017 7:06 pm, edited 2 times in total.
PhDemon
 Post subject: Re: chemistry problem  |  Posted: Thu Mar 02, 2017 7:05 pm

Joined: Wed Jun 26, 2013 10:44 am
Posts: 497
Location: Newcastle-upon-Tyne

 I'm obviously not explaining it very well (sorry about that). Does the "Formal definition" section of this link do a better job?https://en.m.wikipedia.org/wiki/Reaction_rate _________________"The big trouble with dumb bastards is that they are too dumb to believe there is such a thing as being smart"- Kurt Vonnegut, The Sirens of Titan
M_Gabriela
 Post subject: Re: chemistry problem  |  Posted: Thu Mar 02, 2017 7:38 pm

Joined: Tue May 03, 2016 2:25 pm
Posts: 217
Location: Bs As, Argentina

 Ok. I think I understood. Thank you ph!!!
PhDemon
 Post subject: Re: chemistry problem  |  Posted: Thu Mar 02, 2017 7:42 pm

Joined: Wed Jun 26, 2013 10:44 am
Posts: 497
Location: Newcastle-upon-Tyne

 No problem, despite using it a lot myself (it became second nature) I last taught this in 2003 to a first year undergrad class (probably why my explanation wasn't great ) _________________"The big trouble with dumb bastards is that they are too dumb to believe there is such a thing as being smart"- Kurt Vonnegut, The Sirens of Titan
M_Gabriela
 Post subject: Re: chemistry problem  |  Posted: Thu Mar 02, 2017 7:45 pm

Joined: Tue May 03, 2016 2:25 pm
Posts: 217
Location: Bs As, Argentina

 The data given is the rate without dividing it by 2. Thats what you are saying. It's confusing...
PhDemon
 Post subject: Re: chemistry problem  |  Posted: Thu Mar 02, 2017 7:48 pm

Joined: Wed Jun 26, 2013 10:44 am
Posts: 497
Location: Newcastle-upon-Tyne

 You seem to be confusing rate of formation of NO with the rate of reaction, they are not the same (they would be the same if there was not a 2 in front of NO in your equation). Read how rate of reaction is defined in the link I gave, I think it mentions where this 1/n term comes from. _________________"The big trouble with dumb bastards is that they are too dumb to believe there is such a thing as being smart"- Kurt Vonnegut, The Sirens of Titan
M_Gabriela
 Post subject: Re: chemistry problem  |  Posted: Thu Mar 02, 2017 8:13 pm

Joined: Tue May 03, 2016 2:25 pm
Posts: 217
Location: Bs As, Argentina

 Yesssss. I finally understoodddd
PhDemon
 Post subject: Re: chemistry problem  |  Posted: Thu Mar 02, 2017 8:28 pm

Joined: Wed Jun 26, 2013 10:44 am
Posts: 497
Location: Newcastle-upon-Tyne

 Good! Another happy customer _________________"The big trouble with dumb bastards is that they are too dumb to believe there is such a thing as being smart"- Kurt Vonnegut, The Sirens of Titan
M_Gabriela
 Post subject: Re: chemistry problem  |  Posted: Thu Mar 02, 2017 9:54 pm

Joined: Tue May 03, 2016 2:25 pm
Posts: 217
Location: Bs As, Argentina

 I had to explain this to a student Supposedly i should know this,hehehehheheh
PhDemon
 Post subject: Re: chemistry problem  |  Posted: Thu Mar 02, 2017 10:24 pm

Joined: Wed Jun 26, 2013 10:44 am
Posts: 497
Location: Newcastle-upon-Tyne

 If you have a chemistry degree, yes you should! _________________"The big trouble with dumb bastards is that they are too dumb to believe there is such a thing as being smart"- Kurt Vonnegut, The Sirens of Titan
M_Gabriela
 Post subject: Re: chemistry problem  |  Posted: Thu Mar 02, 2017 11:13 pm

Joined: Tue May 03, 2016 2:25 pm
Posts: 217
Location: Bs As, Argentina

 I don't. I have a degree in biology. But it has been a while since i practiced it....
PhDemon
 Post subject: Re: chemistry problem  |  Posted: Fri Mar 03, 2017 12:42 am

Joined: Wed Jun 26, 2013 10:44 am
Posts: 497
Location: Newcastle-upon-Tyne

 That explains a lot! (I'm joking... at work the chemists and physicists like to tease the biologists We get together to take the piss out of the sociology and psychology departments though ) _________________"The big trouble with dumb bastards is that they are too dumb to believe there is such a thing as being smart"- Kurt Vonnegut, The Sirens of Titan
M_Gabriela
 Post subject: Re: chemistry problem  |  Posted: Fri Mar 03, 2017 9:21 am

Joined: Tue May 03, 2016 2:25 pm
Posts: 217
Location: Bs As, Argentina

 We do make fun of psychologists....
 Display posts from previous: All posts1 day7 days2 weeks1 month3 months6 months1 year Sort by AuthorPost timeSubject AscendingDescending
 22 posts • Page 1 of 1

Who is online
 Users browsing this forum: No registered users and 1 guest You cannot post new topics in this forumYou cannot reply to topics in this forumYou cannot edit your posts in this forumYou cannot delete your posts in this forum