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# Enthalpy question watch

1. Can someone please explain this question to me 😰😰😰
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2. What have you done so far?
3. (Original post by LittleBoxes)
Can someone please explain this question to me 😰😰😰
Here you go , if you don't understand anything what I've done, just ask. Hope it helps they'd be harsh if they put this question in the exam :s let's hope not haha. Lol u might need to read it upside down hahah 😂😂
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Don't post full solutions.
Here you go , if you don't understand anything what I've done, just ask. Hope it helps they'd be harsh if they put this question in the exam :s let's hope not haha. Lol u might need to read it upside down hahah 😂😂
How did you form that equation?
6. (Original post by derpz)
How did you form that equation?
It said combustion of propane. As the enthalpy was a standard enthalpy they wanted us to find, we had to assume that all the reactants are completely burnt in oxygen. So, C3H8 + 02 --> h20 +co2 (theses are normally the combustion products of an alkane), and you can now just balance. . If your doing AQA then there is a short sub chapter in the alkanes section, on complete and incomplete combustion .
It said combustion of propane. As the enthalpy was a standard enthalpy they wanted us to find, we had to assume that all the reactants are completely burnt in oxygen. So, C3H8 + 02 --> h20 +co2 (theses are normally the combustion products of an alkane), and you can now just balance. . If your doing AQA then there is a short sub chapter in the alkanes section, on complete and incomplete combustion .
So you would form the equation of the product yourself, and then use the enthalpies given to calcualte the overall enthalpy of combustion for propane?
8. (Original post by derpz)
So you would form the equation of the product yourself, and then use the enthalpies given to calcualte the overall enthalpy of combustion for propane?
Honestly, depends on the questions. That question by OP is slightly harder, cause you have to generate the equation (if you don't, you will not know the moles of each compound). In exam I'm sure they'll give us an equation, they normally do :s XD
Honestly, depends on the questions. That question by OP is slightly harder, cause you have to generate the equation (if you don't, you will not know the moles of each compound). In exam I'm sure they'll give us an equation, they normally do :s XD
I was unsure because one of these came up in a paper we did in class and I was unsure how to answer it. But would I be correct in saying that you form an overall equation for the formation of the product using the equations they've given and then use the values for enthalpy as usual?
10. (Original post by derpz)
I was unsure because one of these came up in a paper we did in class and I was unsure how to answer it. But would I be correct in saying that you form an overall equation for the formation of the product using the equations they've given and then use the values for enthalpy as usual?
Yes, if the equation is not given, and you can't do it mentally. But the problem is, they don't expect you to know a lot of equations, simple equations like formation of co2 and stuff like that they do. So they will most likely give the equation, to not confuse students
Yes, if the equation is not given, and you can't do it mentally. But the problem is, they don't expect you to know a lot of equations, simple equations like formation of co2 and stuff like that they do. So they will most likely give the equation, to not confuse students
Thanks! That helped a lot, but its AQA so we can expect all sorts of confusing and horrendous questions haha
12. (Original post by derpz)
I was unsure because one of these came up in a paper we did in class and I was unsure how to answer it. But would I be correct in saying that you form an overall equation for the formation of the product using the equations they've given and then use the values for enthalpy as usual?
You can't really do a formation equation and use formation values haha XD If they stuck a question in, it would be, what is the enthalpy of formation of methanol, and use the combustion enthalpy values. Also sometimes we can't measure enthalpies of formation for most compounds for example c+o -->co . because the elements don't react directly to give us co, you would also get co2. So normally formation enthalpy values are found using combustion enthalpy values, as most speicies burn readily in oxygen.
13. (Original post by derpz)
Thanks! That helped a lot, but its AQA so we can expect all sorts of confusing and horrendous questions haha
No problem mate good luck

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