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Can someone explain - Chemical Thermodynamics - JEE Main

The difference between \Delta H and \Delta U \left ( \Delta H-\Delta U \right ) , when the combustion of one mole of heptane \left ( 1\right ) is carried out at a temperature T, is equal to :

  • Option 1)

     -4\: RT  

  • Option 2)

     -3\: RT

  • Option 3)

    4\: RT

  • Option 4)

    3\: RT

Answers (1)
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Combution of Heptane is -

 C_{7}H_{18}\left ( l \right )+11O_{2}\left ( g \right )\rightarrow 7CO_{2}\left ( g \right )+8 H_{2}O\left ( l \right )

Change in gaseous moles =7-11=-4

               \Delta H=\Delta U+\Delta n_{g}RT

             \Delta H-\Delta U=-4RT


Option 1)

 -4\: RT  

Option 2)

 -3\: RT

Option 3)

4\: RT

Option 4)

3\: RT

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