Select the two conditions that must be met by a thermochemical equation so that its standard enthalpy change can be written as ÄfH°.

a) One mole of each reactant is used.

b) All substances are at 0°C and 1.013x105 Pa pressure.

c) The reactants are found in their standard states.

d) One kilogram of the substance is produced.

e) One mole of a compound is produced.

f) The values of ÄH for each substance must be specified.

Look at a and c. I also thought 25 C (298.15 K) was specified.

The two conditions that must be met by a thermochemical equation so that its standard enthalpy change can be written as ÄfH° are:

c) The reactants are found in their standard states.
f) The values of ÄH for each substance must be specified.

The two conditions that must be met by a thermochemical equation so that its standard enthalpy change can be written as ÄfH° are:

c) The reactants are found in their standard states.
f) The values of ΔH for each substance must be specified.

Explanation:
a) One mole of each reactant is used - This condition is not directly related to being able to write the standard enthalpy change as ΔfH°. It is important for stoichiometric calculations, but it is not a requirement for writing ΔfH°.

b) All substances are at 0°C and 1.013x105 Pa pressure - While these are standard conditions, they are not specifically required for writing ΔfH°. ΔfH° represents the standard enthalpy change of formation at 25°C and 1 atm pressure, regardless of the specific conditions during the reaction.

c) The reactants are found in their standard states - This condition is necessary to write ΔfH°. The standard state of a substance refers to its pure form at 25°C and 1 atm pressure. To calculate ΔfH°, all reactants must be in their standard states.

d) One kilogram of the substance is produced - This condition is not directly related to writing ΔfH°. The standard enthalpy change of formation is expressed per mole of a compound, not per kilogram.

e) One mole of a compound is produced - This condition is not directly related to writing ΔfH°. The standard enthalpy change of formation is expressed per mole of a compound, so this condition is generally true for ΔfH° calculations.

f) The values of ΔH for each substance must be specified - This condition is necessary to write ΔfH°. The standard enthalpy change of formation, ΔfH°, is determined by the difference in enthalpies between the reactants and the products, so the ΔH values for each substance must be known.

Therefore, the correct conditions for writing the standard enthalpy change as ΔfH° are:
c) The reactants are found in their standard states.
f) The values of ΔH for each substance must be specified.

a

c