A heat of formation table gives the number of kilojoules evolved or absorbed when a mole (gram-formula mass) of the compound in question is formed by the direct union of its elements. In this book a positive number indicates that heat is absorbed and a negative number that heat is evolved. It makes some difference whether the compounds formed are in the solid, liquid, or gaseous state. Unless otherwise indicated (g = gas, 
= liquid), the compounds are in the solid state. If the heat of formation is a large number preceded by a minus sign, the combination is likely to occur spontaneously and the reaction is exothermic. If, on the other hand, the number is small and negative or is positive, heat will be needed to get the reaction to proceed at any noticeable rate.
這句可以先翻譯在提共解釋(yellow lebal) 1它有一些不同無論所形成的化合物是固體，液體或氣體狀態 ,他是說哪裡不同?是joules 還是enthalpy ?怎麼不同在solid, liquid, or gaseous state
2當數值很小為負或正，則需要熱量以使反應以任何顯著的速率進行? 這句畫是在說甚麼
combination reaction 有一定就是放熱還是吸熱反應? 為甚麼combination reaction 的 heat of formation is negative???
decomposition reaction 有一定就是放熱還是吸熱反應? 為甚麼decomposition reaction 的 heat of formation is also negative???
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