At a certain temperature the rate of this reaction is first order in HI with a rate constant of : 7.21s-1

2HI (g) â H2 (g) + I2 (g)

Suppose a vessel contains HI at a concentration of 0.440M

Calculate the concentration of HI in the vessel 0.210 seconds later. You may assume no other reaction is important. Round your answer to 2 significant digits.

C HI = 0.1 M ... 0.210 second later

Explanation:

2 HI (g) = H2 (g) + I2 (g)

∴ order (∝) = 1

∴ κ = 7.21 s-1

∴ Cao = 0.440 M ... initial concentration of HI

∴ t = 0.210 s

rate of this reaction (r):

⇒ - ra = κ. (Ca) ∧∝ ... ∝ = 1

⇒ - ra = κ. Ca = - δCa/δt

⇒ - δCa/Ca = κ.δt

⇒ - ∫ δCa/Ca = κ ∫δt

⇒ Ln Cao/Ca = κ. t

⇒ Cao/Ca = e∧ (κ. t)

⇒ Ca = Cao/e∧ (κ. t)

⇒ Ca = (0.44) / e∧ (7.21*0,21)

⇒ Ca = 0.0968 M

⇒ Ca = 0.1 M