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The relationships between the heats of reaction, pyrolysis and gasification are examined for vaporizing and charring materials. During burning of thermally thick, vaporizing materials the heat of gasification hg E qiet/m biW is equal to the heat of pyrolysis hp. However, no simple relationship exists between h and hp during the burning of charring materials. Solutions for pyrolysis of cellufose are obtained using a one dimensional, numerical model with material properties estimated from the literature. For this material it is found that after an initial transient hg is about twice h For a semi-infinite slab the value of h g then remains nearly constant; for a finite slab t%e value of h may decrease with time to values less than hp. Changes in the assumed chemical reaction rate are found to have a minor effect on hg. The heat of gasification is also relatively insensitive to changes in the char density and thermal conductivity. The variation of h with time is nearly independent of the assumed heat of reaction, but the magnitude of kg varies almost directly with the value of the heat of reaction. Changes in the incident heat flux give corresponding changes in the gasification rate, but much smaller changes in the heat of gasification.