Standard state of a molecular substance

We define the standard state of a molecular substance at temperature T as the state of a pure substance at this temperature, under 1 bar of pressure, in the aggregation state that it has naturally under these conditions. 

If it is a solid, it will be of a stable crystallographic variety. For example, the standard state of carbon at 25°C is graphite. 

Liquids, as well as gases, are considered as being in the same aggregation state. 

In the standard state, the behavior of a gas will be considered as that of a perfect gas, even if at a pressure of 1 bar and at the chosen temperature, the actual behavior of the gas is not the same as the behavior of a perfect gas. 

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