Chemical Thermodynamics Question 425
Question: Diborane is a potential rocket fuel which undergoes combustion according to the equation $ B_2H_6( g )+3O_2( s )\xrightarrow{{}}B_2O_3( s )+3H_2O( g ) $ Calculate the enthalpy change for the combustion of diborane. Given
(i) $ 2B(s)+\frac{3}{2}O_2(g)\xrightarrow{{}}B_2O_3(s); $
$ \Delta H=-1273kJ $ per mol (ii) $ H_2(g)+\frac{1}{2}O_2(g)\xrightarrow{{}}H_2O(l); $
$ \Delta H=-286kJ $ per mol (iii) $ H_2O( l )\xrightarrow{{}}H_2O( g ); $
$ \Delta H=44kJ $ per mol (iv) $ 2B(s)+3H_2(g)\xrightarrow{{}}B_2H_6(g); $
$ \Delta H=36kJ $ per mol
Options:
A) $ +2035kJ $ per mol
B) $ -2035kJ $ per mol
C) $ +2167kJ $ per mol
D) $ -2167kJ $ per mol
Show Answer
Answer:
Correct Answer: B
Solution:
- For the equation $ B_2H_6( g )+3O_2( g )\xrightarrow{{}}B_2O_3( g )+3H_2O( g ) $ Eqs. (i) + 3 (ii) + 3 (iii) - (iv) $ \Delta H=-1273+3( -286 )+3( 44 )-36 $
$ =-1273-858+132-36 $
$ =-2035kJ/mol $
