You can search the relevant meaning of the availability condition for thermodynamic system in the wikipedia since there's so much to learn and laws of thermodynamic equilibrium that explains what and those condition works.
Enthalpy is a thermodynamic property of a thermodynamic system.
please read the 3 kinds of thermodynamic system maybe it can help you to recognize and you can identify which one can be described. http://www.greenserveuk.com/
Heat Flow and Energy.
The heat supplied to a system can increase its internal energy if no work is extracted from the system. If any work is done by the system, then the increase in internal energy will be less than the heat supplied to the system. The thermodynamic variable defined by the zeroeth law is Temperature.
There are three laws of thermodynamics, not inlcluding the understood fourth law. Thermodynamics is the study of how energy is transferred in a system.
Thermodynamic equilibrium is when the inputs and outputs of a system is equal. This may be in terms of heat energy or in terms of liquid/gas flow.
there are three systems : 1 open system 2 close system 3 isolated system
Entropy
that what is the system type you are working on
availability of soil,sunlight,minerals,favourable climatic conditions,
that what is the system type you are working on
Loss of system availability