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    Hiya,

    Basically I'm trying to do some questions on AS Level enthalpy of combustion.

    2 particular ones I'm stuck on is:

    1) Why is a student's value of enthalpy of combustion is much lower than that given in a data book?
    2) Why soot will lead to a low value of enthalpy of combustion?
    3) Why the spirit lamp and ethanol lost mass even when not in use?

    Thank you so much in advance!
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    (Original post by Kosovarja94)
    Hiya,

    Basically I'm trying to do some questions on AS Level enthalpy of combustion.

    2 particular ones I'm stuck on is:

    1) Why is a student's value of enthalpy of combustion is much lower than that given in a data book?
    2) Why soot will lead to a low value of enthalpy of combustion?
    3) Why the spirit lamp and ethanol lost mass even when not in use?

    Thank you so much in advance!
    1. Why does a cup of coffee go cold?
    2. What causes soot (it's carbon)
    3. Do the pavements dry after a rainstorm?
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    (Original post by charco)
    1. Why does a cup of coffee go cold?
    2. What causes soot (it's carbon)
    3. Do the pavements dry after a rainstorm?
    Sorry, but I have no idea where this is going.............
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    Think it through, it makes perfect sense!
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    (Original post by boromir9111)
    Think it through, it makes perfect sense!
    Sorry, I still can't get it. Thanks for your help though.
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    (Original post by Kosovarja94)
    Sorry, I still can't get it. Thanks for your help though.
    Don't you know why a cup of coffee goes cold?

    Come on.. work it out!
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    (Original post by Kosovarja94)
    Hiya,

    Basically I'm trying to do some questions on AS Level enthalpy of combustion.

    2 particular ones I'm stuck on is:

    1) Why is a student's value of enthalpy of combustion is much lower than that given in a data book?
    2) Why soot will lead to a low value of enthalpy of combustion?
    3) Why the spirit lamp and ethanol lost mass even when not in use?

    Thank you so much in advance!
    I think charco is right - you should think. Its nice to see constructive help rather than just someone telling the answers. Its much more rewarding to come up with the answer yourself after thinking about it rather than just being told the answer. Here's some more help, as you don't seem to be getting it.

    1) Coffee goes cold because it's hot and its surroundings is cooler. Bearing in mind that combustion is burning stuff...

    2)What is the formula for ethanol's combustion? So where did the soot (remember, it's carbon) come from according to the reaction? So what hasn't the ethanol done?

    3)Pavements do dry after a rainstorm. Why? What has happened to the water? And how does this relate to the ethanol?

    Quote me if you come up with the answer or if you wnat more help
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    (Original post by qiaoyu.he)
    I think charco is right - you should think. Its nice to see constructive help rather than just someone telling the answers. Its much more rewarding to come up with the answer yourself after thinking about it rather than just being told the answer. Here's some more help, as you don't seem to be getting it.

    1) Coffee goes cold because it's hot and its surroundings is cooler. Bearing in mind that combustion is burning stuff...

    2)What is the formula for ethanol's combustion? So where did the soot (remember, it's carbon) come from according to the reaction? So what hasn't the ethanol done?

    3)Pavements do dry after a rainstorm. Why? What has happened to the water? And how does this relate to the ethanol?

    Quote me if you come up with the answer or if you wnat more help
    1) Because it was incomplete combustion and because there was heat loss to the surroundings, thermometer and calorimeter.

    2) It means that incomplete combustion took place and some of the ethanol did not burn completely to carbon dioxide and water.

    3) Because some of the ethanol evaporates therefore, the spirit lamp and ethanol lose mass.

    Correct at all????
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    (Original post by Kosovarja94)
    1) Because it was incomplete combustion and because there was heat loss to the surroundings, thermometer and calorimeter.

    2) It means that incomplete combustion took place and some of the ethanol did not burn completely to carbon dioxide and water.

    3) Because some of the ethanol evaporates therefore, the spirit lamp and ethanol lose mass.

    Correct at all????
    yep!!
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    (Original post by qiaoyu.he)
    yep!!
    Wohoooooo! Thanks!
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    Btw is this correct too?

    Question: volume of water = 200cm3 mass of water = 200g

    What assumption is being made about water to be able to state that its mass is numerically equal to its volume?


    - That the mass of water is the same as its volume????
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    (Original post by Kosovarja94)
    Btw is this correct too?

    Question: volume of water = 200cm3 mass of water = 200g

    What assumption is being made about water to be able to state that its mass is numerically equal to its volume?


    - That the mass of water is the same as its volume????
    It contains no impurities is what they want I think.
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    (Original post by Kosovarja94)
    Btw is this correct too?

    Question: volume of water = 200cm3 mass of water = 200g

    What assumption is being made about water to be able to state that its mass is numerically equal to its volume?


    - That the mass of water is the same as its volume????
    I think the assumption is that the density of water is exactly 1.00g per cm3

    .. which it isn't, except at one fixed temperature (4ºC)
 
 
 
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