Dear Student, The reactions involved are: Combustion of benzene - C6H6 + 152O2 → 6CO2 + 3H2O ; ∆Hf=-3267 kJ mol-1Or, 6CO2 + 3H2O →C6H6 + 152O2 ,∆Hf=3267 kJ mol-1 --1Formation of carbon dioxide -C + O2→CO2 ; ∆Hf= -393 5 kJ mol-1 --2Formation of water:H2 + 12O2→H2O ; ∆Hf = -285 83 kJ mol-1 --3Formation of benzene:6C + 3H2→C6H6 Now, Multiplying 3 by 3 and 2 by 6, 3H2 + 32O2→3H2O ;∆Hf = -285 83 kJ x 3 =-857 49 kJ mol-16C + 6O2→6CO2 ; ∆Hf= -393 5 x 6 =-2361 kJ mol-16CO2 + 3H2O →C6H6 + 152O2 ,∆Hf=3267 kJ mol-1Adding the three equations, we get:6C + 3H2→C6H6 ; ∆H = 3267 - 2361 - 857 49=48 51 kJ mol-1Thus, the heat of formation of benzene is 48 51 kJ mol-1 Regards

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Dear Student,

The reactions involved are:

C o m b u s t i o n o f b e n z e n e - C_{6} H_{6} + \frac{15}{2} O_{2} \to 6 C O_{2} + 3 H_{2} O; ∆ H_{f} = - 3267 k J m o l^{- 1} O r, 6 C O_{2} + 3 H_{2} O \to C_{6} H_{6} + \frac{15}{2} O_{2}, ∆ H_{f} = 3267 k J m o l^{- 1} - - 1 F o r m a t i o n o f c a r b o n d i o x i d e - C + O_{2} \to C O_{2}; ∆ H_{f} = - 393.5 k J m o l^{- 1} - - 2 F o r m a t i o n o f w a t e r : H_{2} + \frac{1}{2} O_{2} \to H_{2} O; ∆ H_{f} = - 285.83 k J m o l^{- 1} - - 3 F o r m a t i o n o f b e n z e n e : 6 C + 3 H_{2} \to C_{6} H_{6} N o w, M u l t i p l y i n g 3 b y 3 a n d 2 b y 6, 3 H_{2} + \frac{3}{2} O_{2} \to 3 H_{2} O; ∆ H_{f} = - 285.83 k J x 3 = - 857.49 k J m o l^{- 1} 6 C + 6 O_{2} \to 6 C O_{2}; ∆ H_{f} = - 393.5 x 6 = - 2361 k J m o l^{- 1} 6 C O_{2} + 3 H_{2} O \to C_{6} H_{6} + \frac{15}{2} O_{2}, ∆ H_{f} = 3267 k J m o l^{- 1} A d d i n g t h e t h r e e e q u a t i o n s, w e g e t : 6 C + 3 H_{2} \to C_{6} H_{6}; ∆ H = 3267 - 2361 - 857.49 = 48.51 k J m o l^{- 1} T h u s, t h e h e a t o f f o r m a t i o n o f b e n z e n e i s 48.51 k J m o l^{- 1}

Regards

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