The thermodynamics of ethanol steam reforming is considered in terms of response reactions (RERs). These have the property of being independent of the usually arbitrary initial choice of a set of independent reactions, and follow in a natural way from the fundamental equations of chemical thermodynamics. A simple algorithm is proposed for deriving a unique set of RERs, which can be used to rationalize the effect of process variables on steam reforming of ethanol to produce hydrogen. Further, from sensitivity analysis, the dominant reactions in the system can be identified and used in subsequent thermodynamic and kinetic analysis. These are usually arrived at through guess work. At or above 700-800 K, and high water/ethanol ratios the desired reaction of ethanol steam reforming can be made predominant and the effect of undesirable side reactions can be minimized.