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What is the difference between these two?
Ryan Fang 1D wrote:What is the difference between these two?
Standard heat of combustion is the change in enthalpy of a substance when it undergoes complete combustion with oxygen, while standard heat of formation is the change in enthalpy when 1 mole of a compound or substance in its standard state is formed from its base elements in their standard state. So basically one measures the enthalpy of combustion and the other measures the enthalpy of forming a compound or substance.
The standard heat of combustion will always be negative since the reaction will be giving off heat as it breaks the chemical bonds. The heat of formation should always be positive since it will be taking in heat in order to produce the chemical bonds. They can be related to one another by using the sum of the heat of formation for the products and the sum of the heat of formation for the reactants and taking the difference (Hess's law) will give you the heat of combustion.
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