qwurtie Posted March 15, 2013 Author Share Posted March 15, 2013 ok, i tried ANOTHER way and got 388.9 again. so if anyone could confirm, thatd be good. :3 Link to comment Share on other sites More sharing options...
qwurtie Posted March 15, 2013 Author Share Posted March 15, 2013 zomg, just realised theyve just rounded up im hungry, i havent had lunch ok Link to comment Share on other sites More sharing options...
Mikaissocoollike Posted March 15, 2013 Share Posted March 15, 2013 zomg, just realised theyve just rounded up im hungry, i havent had lunch ok Link to comment Share on other sites More sharing options...
qwurtie Posted March 15, 2013 Author Share Posted March 15, 2013 I was getting so annoyed Still dont know why my first calculation doesnt work though Link to comment Share on other sites More sharing options...
Mikaissocoollike Posted March 15, 2013 Share Posted March 15, 2013 I was getting so annoyed Still dont know why my first calculation doesnt work though I would help but I don;t even do physics and I honestly don't get it Link to comment Share on other sites More sharing options...
qwurtie Posted March 15, 2013 Author Share Posted March 15, 2013 I would help but I don;t even do physics and I honestly don't get it It's ok :3 and I just figured out what I was doing wrong Link to comment Share on other sites More sharing options...
qwurtie Posted March 15, 2013 Author Share Posted March 15, 2013 CAN SOMEONE HELP WITH QUESTION 5 PLEASE, it's driving me crazy, I cant figure out what to do http://www-pvhs.stjohns.k12.fl.us/teachers/veatchd/12F0080F-0118C716.19/Stat%2BEq%2BWS.pdf This is how far I get Horizontally: T1 Cos30 = T2 Cos50 = 0 resultant force Vertically: T1 Sin30 + T2 Sin50 = 1000N But then I dont know how to work out the rest Is that right so far? Link to comment Share on other sites More sharing options...
qwurtie Posted March 15, 2013 Author Share Posted March 15, 2013 I got it it got it i got it :excite: aahhh I can chill now :333 Link to comment Share on other sites More sharing options...
astor Posted March 15, 2013 Share Posted March 15, 2013 I got it it got it i got it :excite: aahhh I can chill now :333 Link to comment Share on other sites More sharing options...
Lilasko Posted March 23, 2013 Share Posted March 23, 2013 Anyone feeling like they would want to correct my french text? Link to comment Share on other sites More sharing options...
lemontine Posted May 20, 2013 Share Posted May 20, 2013 Can someone translate: "My older sister wants to know if you know who MIKA is. He's the guy who sings "Elle Me Dit." into french for me please?? Link to comment Share on other sites More sharing options...
Alie Posted May 20, 2013 Share Posted May 20, 2013 Can someone translate: "My older sister wants to know if you know who MIKA is. He's the guy who sings "Elle Me Dit." into french for me please?? Ma soeur aînée veut savoir si tu sais qui est Mika. C'est le gars qui chante "Elle me dit." That's how I would translate it. Link to comment Share on other sites More sharing options...
Ellenowl Posted May 25, 2013 Share Posted May 25, 2013 When doing enthalpy calculations with given enthalpies of combustion or formation, how do you work out whether to take products from reactants or reactants from products? My teacher really confused me about this! Link to comment Share on other sites More sharing options...
DerMoment1608 Posted May 25, 2013 Share Posted May 25, 2013 Did you make it with the "reaction triangle" or only with formulas? I do it with the reaction triangle because I get confused with the formulas all the time, too, and I think it's much easier with the reaction triangle. With the reaction triangle it's only necessary that your arrows are in the right direction, it must be: And than you only need to add up the small arrows and you have your enthalpy of the reaction with the big arrow. A = B + C And if one arrow is in the wrong direction, you only have to switch the sign A = (-B) + C For example if you want Hf (C5H10O5), and given are Hc (C5H10O5) = -2130 kJ/mol and Hf (CO2) = -394 KJ/mol and Hf (H20) = -286 kJ/mol H = (-3400) + (- - 2130) = -3400 + 2130 = - 1270 kJ/mol It's "- - 2130" because the arrow is in the wrong direction. And it's totally unimportant how you write your triangle, you don't need to worry to think about which reaction must be the "big-arrow-reaction", you just need to look that your arrows are in the right direction in the triangle, depending on what is given. (- H) + (-3400) = -2130 - H = 1270 H = - 1270 kJ/mol Again "- H" because now this arrow is in the wrong direction. I hope that was what you wanted to know and it was understandable in English Link to comment Share on other sites More sharing options...
lollipop161 Posted May 25, 2013 Share Posted May 25, 2013 Omg I'm learning the same thing right now... liked the "reaction triangle"! Hate Physical Chemistry!!! But Organic Chemistry is the worst:doh: Link to comment Share on other sites More sharing options...
astor Posted May 25, 2013 Share Posted May 25, 2013 Hess' Law! Enthalpy profiles! We're all on the same topics Ellenowl, what exam board are you on for chemistry? Link to comment Share on other sites More sharing options...
Ellenowl Posted May 25, 2013 Share Posted May 25, 2013 Hi Astor, I'm doing AQA. What about you? Thanks so much for your thorough answer Dermoment, it is the kind of thing I'm stuck on. I'll look again in the morning because it's making me freak out now. I actually find organic chemistry much easier than Hess' cycle chemistry, but that might be because I have a different teacher for it. Link to comment Share on other sites More sharing options...
Yasi Posted May 26, 2013 Share Posted May 26, 2013 (edited) When doing enthalpy calculations with given enthalpies of combustion or formation, how do you work out whether to take products from reactants or reactants from products? My teacher really confused me about this! You can always use: SUM (Hproducts) - SUM (Hreactants) it's pretty easy: for example:find the standard enthalpy of reaction:4NH3+3O2= 2N2+6H2O delta H for H2O:-242 delta H for NH3:-46 solve:4NH3+3O2=4X(-46)+(3X0)=-184 2N2+6H2O=(2X0)+6X(-242)=-1452 delta H total:SUM (Hproducts) - SUM (Hreactants)=(-1452)-(-184)=-1268 KJ It can be confusing sometimes,actually,it was the only reason I couldn't get world gold medal for chemistry 2 years ago! Edited May 26, 2013 by Yasi Link to comment Share on other sites More sharing options...
Ellenowl Posted May 26, 2013 Share Posted May 26, 2013 You can always use:SUM (Hproducts) - SUM (Hreactants) it's pretty easy: for example:find the standard enthalpy of reaction:4NH3+3O2= 2N2+6H2O delta H for H2O:-242 delta H for NH3:-46 solve:4NH3+3O2=4X(-46)+(3X0)=-184 2N2+6H2O=(2X0)+6X(-242)=-1452 delta H total:SUM (Hproducts) - SUM (Hreactants)=(-1452)-(-184)=-1268 KJ It can be confusing sometimes,actually,it was the only reason I couldn't get world gold medal for chemistry 2 years ago! The problem is that you sometimes have to do reactants-products! I think if you're asked enthalpy of combustion you do reactants-products and you do products-reactants for enthalpy of formation. I hope that's the right way round! The other problem for me is when they ask you to calculate one of the values in the triangle! Glad I'm not the only one who finds it confusing! Thanks for your help. Link to comment Share on other sites More sharing options...
Yasi Posted May 26, 2013 Share Posted May 26, 2013 The problem is that you sometimes have to do reactants-products! I think if you're asked enthalpy of combustion you do reactants-products and you do products-reactants for enthalpy of formation. I hope that's the right way round! The other problem for me is when they ask you to calculate one of the values in the triangle! Glad I'm not the only one who finds it confusing! Thanks for your help. If the data is entalpies of formation, it's products minus reactants. If the data is enthalpies of combustion, it's reactants minus products. Sorry,I don't remember anything about triangle,actually,we never solved problems that way! your welcome,hope it helped:thumb_yello: Link to comment Share on other sites More sharing options...
astor Posted May 26, 2013 Share Posted May 26, 2013 Hi Astor, I'm doing AQA. What about you? Thanks so much for your thorough answer Dermoment, it is the kind of thing I'm stuck on. I'll look again in the morning because it's making me freak out now. I actually find organic chemistry much easier than Hess' cycle chemistry, but that might be because I have a different teacher for it. I'm on OCR - dayum, I wondered if we could on be the same one Link to comment Share on other sites More sharing options...
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