Chemical Thermodynamics — Chemistry STD 12 Science — Question
Maharashtra BoardEnglish MediumSTD 12 ScienceChemistryChemical Thermodynamics3 Marks
Question
What is the standard enthalpy of combustion ? Give an example.
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Answer
Standard enthalpy of combustion or standard heat of combustion : it is defined as the enthalpy change when one mole of a substance in the standard state undergoes complete combustion in a sufficient amount of oxygen at constant temperature $(298 K$ ) and pressure ( 1 atmosphere or 1 bar). It is denoted by $\Delta_{ C } H ^0$. E.g. $CH _3 OH _{( l )}+\frac{3}{2} O _{2( g )}= CO _{2( g )}+2 H _2 O$ $\Delta_{ C } H ^0=-726 kJ mol ^{-1}$ ( $\Delta_{ c } H ^0$ is always negative.) [Note: Calorific value : It is the enthalpy change or amount of heat liberated when one gram of a substance undergoes combustion. $\therefore$ Calorific value $=\frac{\Delta_{ f } H^0}{\text { Molar mass }}$
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