Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter
    Offline

    2
    ReputationRep:
    If given the following information, how can one deduce the enthalpy change?

    S(s) + 1.5 O2 (g) --> SO3(g)
    Offline

    13
    ReputationRep:
    That's all the information youre given?
    That's tricky
    Offline

    8
    ReputationRep:
    do you have to give a value or say if it is exo or endo
    • Thread Starter
    Offline

    2
    ReputationRep:
    wait - I also have this information, but I'm still a little confused - I understand what they did, but not why they did it

    S(s) + O2(g) <----> SO2 (g) kJ= -297
    SO2(g) + 1/2 O2 <---->SO3(g) kJ= -92
    Offline

    8
    ReputationRep:
    don't you just add the numbers together?
    because you just follow the steps to make so3
    and its balanced so you don't need to change the numbers
    Offline

    11
    ReputationRep:
    Delta H= (-297)+(-92)
    = -389 kJ
    Offline

    2
    ReputationRep:
    Name:  image.jpg
Views: 66
Size:  505.7 KBDoes anybody know how to work this out? It was from the new Aqa Chem AS paper 2016 Thank You
    Offline

    8
    ReputationRep:
    what i would do is find the mass
    you do this because you know the density is g / cm3
    so just times it by the volume which is 0.5 dm3 (remember to convert it)
    once you have the mass you can find the mols of ethanol
    then times that by the enthalpy change
    im not too sure if I'm right tho
    (Original post by PBC Gyal)
    Name:  image.jpg
Views: 66
Size:  505.7 KBDoes anybody know how to work this out? It was from the new Aqa Chem AS paper 2016 Thank You
    Offline

    2
    ReputationRep:
    (Original post by CrystalSalvatore)
    what i would do is find the mass
    you do this because you know the density is g / cm3
    so just times it by the volume which is 0.5 dm3 (remember to convert it)
    once you have the mass you can find the mols of ethanol
    then times that by the enthalpy change
    im not too sure if I'm right tho
    Yeah that's what I think too but I don't know how to calculate the mass, sorry for the mess in my working out, but with the converting and stuff it's all confusing 😳
    Offline

    8
    ReputationRep:
    (Original post by PBC Gyal)
    Yeah that's what I think too but I don't know how to calculate the mass, sorry for the mess in my working out, but with the converting and stuff it's all confusing 😳
    0.5 dm3 is 500 cm3 to times that by the density
    Offline

    4
    ReputationRep:
    Calculate mass of ethanol in grams
    Calculate the moles of ethanol (moles=mass/mr)
    Divide enthalpy change by the moles.
    Offline

    2
    ReputationRep:
    (Original post by Kyle03)
    Calculate mass of ethanol in grams
    Calculate the moles of ethanol (moles=mass/mr)
    Divide enthalpy change by the moles.

    Ohh okay I've just done that and I got 0.16KJ and I don't think that seems right 😮
    Offline

    2
    ReputationRep:
    (Original post by CrystalSalvatore)
    0.5 dm3 is 500 cm3 to times that by the density
    Ohh okay thanks and then I did that and got moles from it by dividing by Mr and then dividing it by 1000 to put it in KJ but I got 0.16KJ and it doesn't seem right 🤔
    Offline

    8
    ReputationRep:
    (Original post by PBC Gyal)
    Ohh okay thanks and then I did that and got moles from it by dividing by Mr and then dividing it by 1000 to put it in KJ but I got 0.16KJ and it doesn't seem right 🤔
    why did you divide the moles by 1000?
    when you have the moles you times it by the enthalpy change because its Kj/Mol so if you times is by the mol it would leave the Kj
    Offline

    2
    ReputationRep:
    (Original post by CrystalSalvatore)
    why did you divide the moles by 1000?
    when you have the moles you times it by the enthalpy change because its Kj/Mol so if you times is by the mol it would leave the Kj
    Ohh okay thanks that makes sense, so my answer would be 159.86KJ
    Offline

    2
    ReputationRep:
    (Original post by CrystalSalvatore)
    what i would do is find the mass
    you do this because you know the density is g / cm3
    so just times it by the volume which is 0.5 dm3 (remember to convert it)
    once you have the mass you can find the mols of ethanol
    then times that by the enthalpy change
    im not too sure if I'm right tho
    I am so confused so how do you work it out i dont get it.
    Offline

    20
    ReputationRep:
    (Original post by Kyle03)
    Calculate mass of ethanol in grams
    Calculate the moles of ethanol (moles=mass/mr)
    Divide enthalpy change by the moles.
    once you have the moles, multiply them by the enthalpy of combustion.
    Offline

    2
    ReputationRep:
    (Original post by the bear)
    once you have the moles, multiply them by the enthalpy of combustion.
    Oh I divided the enthalpy of combustion by the moles not multiplied it?
    Offline

    20
    ReputationRep:
    (Original post by PBC Gyal)
    Oh I divided the enthalpy of combustion by the moles not multiplied it?
    :spank:
    Offline

    2
    ReputationRep:
    (Original post by the bear)
    :spank:
    😂😂😂but why would you multiply?
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Did TEF Bronze Award affect your UCAS choices?
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

    Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

    Quick reply
    Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.