1. 1  an implement, such as a hammer, saw, or spade, that is used by hand. 2  a power-driven instrument; machine tool. ( 3 in combination): a toolkit.
The standard enthalpy of combustion is the enthalpy change when one mole of a reactant completely burns in excess oxygen under standard thermodynamic conditions (although experimental values are usually obtained under different conditions and subsequently adjusted).he standard enthalpy of combustion is the enthalpy change when one mole of a reactant completely burns in excess oxygen under standard thermodynamic conditions (although experimental values are usually obtained under different conditions and subsequently adjusted).
The standard enthalpy of reaction (denoted Î´ r H â) is the enthalpy change that occurs in a system when one mole of matter is transformed by a chemical reaction under standard conditions.hat is, the enthalpy of a reaction at constant volume is equal to the change in the internal energy (Î´ E) of the reacting system. The thermal change that occurs in a chemical reaction is only due to the difference in the sum of internal energy of the products and the sum of the internal energy of reactants.