ABSTRACT
When we disturb a system from its original equilibrium situation, we know that a transport process must occur to restore the original equilibrium state, to bring the system to some new equilibrium state, or to take the system to a new non-equilibrium state. The disturbance is always in the form of a change in one of the conserved quantities of the system (momentum, energy, mass, charge, etc.) and can be tracked by measuring a change in one of the state variables of the system such as the temperature, pressure, voltage, or mole fraction. These changes set up a spatial variation in the state variable also called a gradient. The particles, molecules, electrons, atoms, etc., move in response to this gradient in an attempt to diminish the gradient and restore equilibrium.
