Endothermic reaction carbohydrates

As discussed above, the pyrolysis of biomass at high temperature (>1000 °C) results in the formation of synthesis gas, a valuable mixture of CO and H2. The decomposition of carbohydrate to synthesis gas is an endothermic reaction since the heating value of product is —125% of that of the feedstock (Reaction 1). The reaction becomes nearly thermo-neutral upon burning about 1/4 of the products. Since the thermodynamics favors the combustion of H2 over CO, the gasification reaction resemble the theoretical Reaction (2). Indeed numerous gasification processes feed 02 or air to drive the gasification reaction. 

Perhaps most interesting are endothermic reactions that result in products of less entropy (Case IV). What is notable about these reactions is that they will not occur on their own without the continued input of energy. Also, the products of these reactions can be complex molecules. The classic example is photosynthesis, which is the biochemical reaction by which plants use solar energy to create carbohydrates and oxygen from carbon dioxide and water, as represented by the following equation ... 

If the reaction is reversed and the carbohydrate is burnt to give carbon dioxide and water 112,000 calories of heat is evolved for each mole of carbon dioxide. Therefore, the union of carbon dioxide and water to give a carbohydrate and oxygen must absorb 112,000 caloiies. Since the energy of activation of an endothermic reaction must be at least as great as the heat absorbed,60 it is evident that at least 112,000 calories per mole must be supplied—and perhaps much more than this. Ultraviolet radiation below 2,400 A... 

All these reactions are highly endothermic. The products of these reactions are high calorific fuels. In nature fixation of COs is a dark process although initiated by light induced chain of reactions. Except in some special plants like rubber, C02 is still not completely reduced. Carbohydrates are the common stored products. Rubber plants produce hydrocarbons. 

Condensed-Phase Mechanisms. The mode of action of phosphorus-based flame retardants in cellulnsic sy stems is probably best understood. Cellulose decomposes by a noncalalyzed route lo tarry depolymerization products, notably levoglucosan, which then decomposes to volatile combustible fragments such as alcohols, aldehydes, ketones, and hydrocarbons. However, when catalyzed by acids, the decomposition of cellulose proceeds primarily as an endothermic dehydration of the carbohydrate to water vapor and char. Phosphoric acid is particularly efficaceous in this catalytic role because of its low volatility (see Phosphoric Acids and Phosphales). Also, when strongly heated, phosphoric acid yields polyphosphoric acid which is even more effective in catalyzing the cellulose dehydration reaction. The flame-retardanl action is believed to proceed by way of initial phosphory lation of the cellulose. 

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