Cyclohexane C6H12 can decomposed to propene C6H12 2 CH3CHCH

Cyclohexane (C₆H₁₂) can decomposed to propene :

C₆H₁₂ 2 CH₃CH=CH₂

The graph shows the concentration of cyclohexane versus time as measured by UV-Vis spectroscopy.

a) Calculate the average rate of reaction between 10. and 30. s

b) For this time interval, what is the rate for the formation of propene (H₃CH=CH₂) ?   

c) What is the half-life for the decomposition of cyclohexane?  

d) Assuming the reaction shown above is also the elementary step. If the initial concentration of cyclohexane is 0.24M, what is the concentration of cyclohexane at 100 s?  

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Solution

For the decomposition reaction of cyclohexane to propene

a) average rate between 10 and 30 s

= -(0.082 - 0.165)/20

= 0.00415 M/s

b) rate of formation of propene = 2 x 0.00415 = 0.00830 M/s

c) half-life t1/2 = ln(2)/0.00830 = 83.51 s

d) at t = 100 s

concentration of cycohexane = 0.005 M