Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Calculating enthalpies of combustion from a bomb calorimeter?

  1. Oct 23, 2012 #1
    1. The problem statement, all variables and given/known data

    A sample of K (s) of mass 2.740g undergoes combustion in a constant volume calorimeter at 298.15K . The calorimeter constant is 1849 J/K , and the measured temperature rise in the inner water bath containing 1450 of water is 1.60K
    Calculate the enthalpy of formation for K2O

    2. Relevant equations

    ΔH(combustion) = C(cal)ΔT +nC(H2O)ΔT

    n= # of moles
    3. The attempt at a solution

    I pretty much know already how to do this problem and I've worked it out fully (I figured out the enthalpy of combustion and then divided by the number of moles of K I had), but I realized my answer was off by a factor of two.

    Is this because the balanced equation is 2K + (1/2) O2 ----> K2O
    and it takes two moles of potassium to make a mole of K2O?

    I'm just unsure of when I should have taken the factor of two into account (assuming that my reasoning is correct)
  2. jcsd
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted