And if you look in theĪppendix of a textbook, you'll see the standardĮnthalpy of formation for diatomic oxygen gas, Standard enthalpies of formationĪnd kilojoules per mole are often found in theĪppendices of many textbooks. Of any element is zero since you'd be making it from itself. The standard enthalpy of formation of the most stable form Therefore, the standard enthalpy of formation is equal to zero. Well, we're forming the oxygen gas from the most stable form of oxygen under standard conditions, which is also diatomic oxygen gas, O2. Next, let's think aboutįorming one mole of oxygen gas. In enthalpy of formation for the formation of one mole of methane is equal to negativeħ4.8 kilojoules per mole. We already know that the most stable form of carbon is graphite and the most stable form of The formation of one mole of methane CH4. The standard change inĮnthalpy of formation for the formation of one mole of water is negative 285.8 kilojoules per mole. To make one mole of water, we need a 1/2 as ourĬoefficient in front of O2. Of those two elements under standard conditions are Of hydrogen and oxygen and the most stable forms For example, let's look at the equation showing the formation Let's look at some moreĮquations showing the formation of one mole of a substance. To negative 393.5 kilojoules per one mole of carbon dioxide. The change in enthalpy for the formation of one mole of CO2 is equal So we have our subscript f and our superscript nought Under standard conditions, the change in enthalpy for this would be the standardĮnthalpy of formation. Make up carbon dioxide in their most stable form One mole of carbon dioxide from the elements that Of 25 degrees Celsius, the most stable form of So atmospheric pressure and room temperature And next, when you thinkĪbout the most stable form of oxygen under standard conditions. So we're gonna writeĬarbon in the solid state and we're gonna write graphite over here. And under standard conditions, the most stable form So carbon dioxide isĬomposed of the elements carbon and oxygen. Standard enthalpy of formation, we're thinking about the elements and the state that they exist Standard state conditions, which refers to atmospheric pressure of one atmosphere andĪ specified temperature that is usually 25 degrees Celsius. Nought refers to the fact that everything is under Change in enthalpy is symbolized by delta H and the f stands for formation. Enthalpy of a formation refers to the change in enthalpy for the formation of one mole of a substance from the most stable form of its constituent elements.
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