Can someone help me with this question?
what two conditions must be met by a thermochemical equation so that its standard enthalpy change can be given the symbol delta Hf?
http://en.wikipedia.org/wiki/Standard_enthalpy_of_formation
To determine the conditions that must be met by a thermochemical equation in order to represent the standard enthalpy change with the symbol ΔHₒf, we need to understand the concept of standard enthalpy of formation.
The standard enthalpy of formation (ΔHₒf) is the change in enthalpy that occurs when one mole of a compound is formed from its elements in their standard states (at a given temperature and pressure). It serves as a reference point to measure the relative stability of a compound.
In order for a thermochemical equation to have the standard enthalpy change symbol ΔHₒf, it must satisfy two conditions:
1. The equation must represent the formation of one mole of the compound from its elements in their standard states. This means that all the reactants involved should be in their standard states, i.e., in their most stable forms at a specific temperature and pressure. For example, if you are considering the enthalpy change for the formation of water (H₂O), the reactants should be hydrogen (H₂) and oxygen (O₂) in their standard states.
2. The reaction must occur under standard conditions. This usually means that the reaction takes place at a pressure of 1 bar and a temperature of 25 degrees Celsius (298 Kelvin). It is important to note that these standard conditions can vary depending on the context in which the data is being used. So, it is always necessary to specify the conditions.
By meeting these two conditions, a thermochemical equation can provide the standard enthalpy change (ΔHₒf) for the formation of a compound.