Question

For the combustion of C3H8(g) at constant
temperature ΔΗ - ΔU is
(1) - RT
(2) +RT
(3) – 3RT
(4) + 3RT​

Answer 1

answer : option (3) -3RT

explanation : combustion of C3H8 ,

$C_3H_8(g)+5O_2(g)\rightarrow 3CO_2(g)+4H_2O(l)$

from first law of thermodynamics of chemical reaction,

$\Delta H-\Delta U=\Delta n_gRT$

where $\Delta n_g$ = no of moles of gaseous products - no of moles of gaseous reactants.

above reactions,

no of moles of gaseous products = 3

no of moles of gaseous reactants = 5 +1 = 6

so, $\Delta n_g=3-6=-3$

then, ∆H - ∆U = (-3)RT = -3RT

hence, option (3) is correct choice.

Answer 2

Answer:

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