Question

The heat of combustion of methane(g) at constant volume is-885 kJ at 298 K,
Calculate the heat of combustion of methane at constant pressure?.
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Answer 1

Answer:

The equation for the heat (Enthalpy of formation of Methane is

C(s)+2H2(g)======>CH4(g)

∆H= ∆E+RT(∆n),

where ∆H= Heat of formation at constant Pressure .

∆E= Heat of formation at constant volume.

Here ∆n= (No.of molecules of GASEOUS products - No.of molecules of GASEOUS reactants)

∆n= 1–2=-1.

So ∆E= ∆H-RT(∆n)=

-75830-(1.986 x300)(-1) =-75830+595.8

=-75234.2 Cal

= -75.2342K.Cal