Difference between AH & Au for the combustion of graphite is
Answers
Combustion of methane means the burning of methane in the presence of oxygen to give carbon dioxide and water.
The balanced reaction for combustion of methane is as follows:
CH
4
(g)+2O
2
(g)→CO
2
(g)+2H
2
O
In such reactions, the change in the number of moles is calculated for gaseous products only.
The number of moles of CH
4
, O
2
ans CO are 1, 1 and 2 respectively as seen from the balanced reaction given above.
Therefore, the change in the number of moles is given by =Δn
g
=n
products
−n
reactants
=1−(2+1) =−2
We know the relation: ΔH=ΔE+Δn
g
RT, where ΔH is the enthalpy change, ΔE is the internal energy change and Δn
g
is the change in the number of moles (as per the law of thermodynamics).
The value of gas constant (R) is 2 cal and temperature is 27
o
C or 300 K (given).
∴ΔH−ΔE=Δn
g
RT=−2×2×300 =−1200 calories
Hence, the difference in ΔH and ΔU for the combustion of methane at 27
o
C is −1200 cal.