[YAPA] entropy

[norma.holowach]

Teachers,
A student asked me a question in which I have not been able to find an answer. 
How is the entropy level of a substance determined? How is the zero value 
defined?  For example, a reference I have gives the entropy(S) of oxygen gas 
at 25 degrees Celsius and 100.00 kPa a value of 205.138 J/(mol*K). How was 
that value determined?

Thank you.

Norma Holowach, M.Ed
National Board Certified Teacher
Praxis III Assessor
Lakeview High School
300 Hillman Drive
Cortland, OH  44410
(330)637-4921
"Connecting with nature is an essential part of being alive."
National Geographic.