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: Enthalpy of Reaction question

  1. Nov 26, 2005 #1
    I've been having trouble understanding some parts of these questions. The question goes like this:

    The "thermite reaction" is highly exothermic. It involves the reaction between Fe2O3 & Al. The reaction produces white-hot, molten iron is a few seconds.
    2 Al + 3/2 O2 --> Al2O3 delta H = -1672 kJ
    2 Fe + 3/2 O2 --> Fe2O3 delta H = -836 kJ​

    a) find the amount of heat liberated in the reaction of one mole of Fe2O3 with Al.
    b) find the amount of heat liberated in the reactino of 1 kg of Fe2O3 with Al.
    c) how many grams of liquid water could be heated from 0C to 100C by the heat liberated per mole of aluminum oxide?

    For a) and b), when I'm trying to find the enthalpy, do I need to apply hess's law to obtain the enthalpy of one mole of Fe2O3 and Al? The part that confuses me is the relevance with Fe2O3 and Al. So far, I've only gotten to figuring out what the target eq'n is.

    2 Al + 2 Fe --> Al2O3 + Fe203 delta H = -836kJ​

    But after determining the target eq'n, I don't know what to do in terms of Fe2O3 and Al for that one mol and similarly with determining 1 kg.
  2. jcsd
  3. Nov 27, 2005 #2


    User Avatar
    Science Advisor
    Homework Helper

    If they want the reaction of the iron oxide with aluminum (you should denote the states of the molecules/atoms involved), your final equation is incorrect. Write the proper equation, and observe on whether the terms in the enthalpy values for each denoted reaction (kJ/mol, kJ/grams or kJ/mol reaction, kJ/mol Al etc....), the rest should be simple, Don't forget to take into account the stoichiometries.
  4. Nov 27, 2005 #3
    So really, it's just a single displacement rxn then between Al and Fe2O3?
  5. Nov 28, 2005 #4


    User Avatar
    Science Advisor
    Homework Helper

    yes, Fe2O3 + 2Al → Al2O3 + 2Fe, I'm sure you can take it from here
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook