Chemical Reactions and Gibbs Free Energy

Every material thing has a standard Gibbs free energy and we can write a similar equation for water  

But when we mix urea and water and completely dissolve it, urea is still there, only somewhat changed its Gibbs energy has changed too [1] and we write 

The correction to the standard Gibbs energy, G , contains the gas constant (used to connect different units), the temperature, and a logarithm of a. We call a the activity, it is telling us how much urea, now mixed with water (and invisible to the naked eye), is active in this mixture. We often do not know or carmot easily measure the activity so we approximate it by concentration  

This is usually a good approximation when the concentration is low, like 10 M or lower. 

Make a note Gibbs energy, standard Gibbs energy, activity. 

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