Chemistry

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Which of the following substances have a standard heat of formation of zero?

O2 at 25.O degrees C and 1 atm
Fe at 1200 degrees C
C2H6 at standard conditions
Cl2 at 2 atm

  • Chemistry -

    O2, Fe and Cl2 should all have zero enthalpy of formation because, they are pure or in diatomic state. However, Fe and Cl2 are not under standard conditions because standard condition is 25degreesC at 1atm. So to me it should be O2.

  • Chemistry -

    O2 is right.

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