1. Which of these compounds give out the most heat (per mole) on combustion?
C6H14, C7H16, C8H18, C9H20, C10H22
Chose C6H14 because it's the most flammable.
2. Thought this question was way too easy. Too easy to be questioned so I decided to check if my answer is correct. How many electrons are found in the outer shell of each carbon atom in the propane molecule? Isn't it still 4?
3. In a coal mine the percentage of methane in air is continually monitored. Intially at 0 hour, there was slighlt below 5% of CH4. It steadily increases to 20% after 5 hours and also, at the fifth hour, it plunged right down to 0% of methane.
What could have caused these changes to happen? Not really sure of this question.
Guys, do help if possible. Thanks.
Originally posted by anpanman:1. Which of these compounds give out the most heat (per mole) on combustion?
C6H14, C7H16, C8H18, C9H20, C10H22
Chose C6H14 because it's the most flammable.
2. Thought this question was way too easy. Too easy to be questioned so I decided to check if my answer is correct. How many electrons are found in the outer shell of each carbon atom in the propane molecule? Isn't it still 4?
3. In a coal mine the percentage of methane in air is continually monitored. Intially at 0 hour, there was slighlt below 5% of CH4. It steadily increases to 20% after 5 hours and also, at the fifth hour, it plunged right down to 0% of methane.
What could have caused these changes to happen? Not really sure of this question.
Guys, do help if possible. Thanks.
1)C10H22. it has the most number of C=C and C-H bonds, which release the most energy when a single mol of the compound is combusted.
C6H14 is the most flammable. nothing wrong with that. but being easy to combust doesn't equate it to it giving the most energy.
2) the carbon atom in propane has now 8 electrons, due to electron sharing with the hydrogen atoms to form a stable octet structure.
3) High concentration of volatile methane gas led to explosion, where all the methane gas are fully combusted, bringing the methane level back down to 0%
1) Not sure about this but i think the largest 1 would give the more energy.
2) Being a molecule, it would have 8 electrons if not it would have been unstable. 3 electrons are shared with 3 H and 1 electorn is shared with 1 C.
3) My guess is methane built up over time which accounts for the increase and most prob an explosion resulted which used up all the methane since methane is a very flammable gas.
Originally posted by deathmaster:1)C10H22. it has the most number of C=C and C-H bonds, which release the most energy when a single mol of the compound is combusted.
They are all C-C bonds since this is an alkane not an alkene
Originally posted by deathmaster:1)C10H22. it has the most number of C=C and C-H bonds, which release the most energy when a single mol of the compound is combusted.
C6H14 is the most flammable. nothing wrong with that. but being easy to combust doesn't equate it to it giving the most energy.
2) the carbon atom in propane has now 8 electrons, due to electron sharing with the hydrogen atoms to form a stable octet structure.
3) High concentration of volatile methane gas led to explosion, where all the methane gas are fully combusted, bringing the methane level back down to 0%
The only answer I have doubts of is question 2. The question is asking me about the outer shell of each carbon atom. They aren't referring to the carbon atoms in the propane molecule. So why must it be 8 electrons? Thanks anyway.
And one more question.
Will C2H3Cl cause bromine water to turn colourless? I know unsaturated hydrocarbons do. For C2H3Cl, it does contain the carbon-carbon double bond, rendering it an unsaturated compound.
Originally posted by anpanman:
The only answer I have doubts of is question 2. The question is asking me about the outer shell of each carbon atom. They aren't referring to the carbon atoms in the propane molecule. So why must it be 8 electrons? Thanks anyway.
And one more question.
Will C2H3Cl cause bromine water to turn colourless? I know unsaturated hydrocarbons do. For C2H3Cl, it does contain the carbon-carbon double bond, rendering it an unsaturated compound.
The question stated carbon atoms in propane right? Once any atom is in a compound, they no longer have their 'own' electrons as they are shared and for stability, they will always have 8 in the outermost shell.
It is an alkene so bromination will take place and decolourise bromine water as its being used up.
I have a question regarding organic chemistry too. Does C2H6 or C2H4 form a giant molecule? I think it is C2H6. Can someone tell me why? If this is wrong, please correct me. Hmm, and if the reacton takes place, are there any other reactants that are needed to form the giant molecule. It would be good if someone could compress this reaction into one simple equation.
Thank you
Didn't know that either ethane or ethene could form a giant molecule. Regardless, ethane is saturated so it is unlikely to ever be able to form or bond with anything else to make anything.
The only 'giant' i can think of would be a polymer and for that, its uses ethene. This will give you the common polymer polyethene (PE).
n C2H4 - > (C2H4)n
Originally posted by anpanman:1. Which of these compounds give out the most heat (per mole) on combustion?
C6H14, C7H16, C8H18, C9H20, C10H22
>>> Which of these compounds give out the most heat (per mole) on combustion? C6H14, C7H16, C8H18, C9H20, C10H22 <<<
Based on bond enthalpies, calculate the formation enthalpies of these hydrocarbon compounds. Also calculate the formation enthalpies of carbon dioxide and water. Apply Hess' Law and balanced stoichiometries to calculate the combustion enthalpies for the hydrocarbons.
Originally posted by UltimaOnline:
>>> Which of these compounds give out the most heat (per mole) on combustion? C6H14, C7H16, C8H18, C9H20, C10H22 <<<
Based on bond enthalpies, calculate the formation enthalpies of these hydrocarbon compounds. Also calculate the formation enthalpies of carbon dioxide and water. Apply Hess' Law and balanced stoichiometries to calculate the combustion enthalpies for the hydrocarbons.
Thats 1 of the parts of physical chemistry i hate alot :p
is this A level chemistry?
Originally posted by LoudnessFZ:is this A level chemistry?
No. It's taught at O Level.
Originally posted by UltimaOnline:
>>> Which of these compounds give out the most heat (per mole) on combustion? C6H14, C7H16, C8H18, C9H20, C10H22 <<<
Based on bond enthalpies, calculate the formation enthalpies of these hydrocarbon compounds. Also calculate the formation enthalpies of carbon dioxide and water. Apply Hess' Law and balanced stoichiometries to calculate the combustion enthalpies for the hydrocarbons.
Hi. May I know what is Hess' Law and stuff? Thanks. :)
Originally posted by anpanman:
Hi. May I know what is Hess' Law and stuff? Thanks. :)
Hess' law states that the enthalpy change for a given reaction is the same regardless of the reaction happening in one step or many steps, provided that the initial states and final states are the same.