1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Can someone help with this problem: Standard enthalpy

  1. May 9, 2006 #1
    Calculate the standard enthalpy change for the reaction

    2C8H18(l)+ 21 O2(g)-->8CO(g)+8CO2(g)+18H2O(l)

    Given:
    2C8H18(l)+25 O2(g)--> 16CO2(g)+18H2O(l) H=-11,020kJ/mol
    2CO(g)+ O2(g)-->2CO2(g) H=-566.0kJ/mol


    I just cant get it to cancel out from the given, to calculate the stardard enthalpy
     
  2. jcsd
  3. May 9, 2006 #2
    In order to find standard enthalpy change u need to work thru the equations given with the enthalpy change and treat as if u r doin simultaneous equations in algebra.

    U need to get the equation on the top from the two below. Since the first given equation has 2C8H18 u do not need to manipulate this one. However for the second one first multiply thru out by 4 since u need 8CO and 8CO2. So after mulitplyin thru out by 4 u get:

    8CO + 4O2 -> 8CO2 H=-2264 kJ/mol

    Inorder to get the equation for which u have to calculate the enthalpy change u need CO on the r.h.s of the equation. Therefore u need to reverse the equation and as such the sign of the enthalpy change for that will also change:

    8CO2 -> 8CO + 4O2 H=2264 kJ/mol

    Now adding this equation with the first given equation u get the required enthalpy change since adding them makes u get the equation on the top.

    2C8H18 + 25O2 -> 16CO2 + 18H2O H=-11020 kJ/mol
    8CO2 -> 8CO + 4O2 H=2264 kJ/mol

    Resulting equation:

    2C8H18 + 21O2 -> 8CO2 + 8CO + 18H2O

    Therefore the enthalpy change=-11020 + 2264 kJ/mol (since u added the
    =-8756 kJ/mol equations)

    :devil:
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Can someone help with this problem: Standard enthalpy
Loading...