Question

For a reaction

2A + B → C ; following data were collected

	[A]/(mol/L)	[B]/(mol/L)	Rate/(mol L−1 min−1)
i)	6 × 10−2	1 × 10−2	0.004
ii)	6 × 10−2	2 × 10−2	0.008
iii)	12 × 10−2	1 × 10−2	0.008

Calculate the overall order of the reaction and rate constant

Answer 1

Rate law for the reaction can be

Rate = [A]^α [B]^β

From first and second observations 

0.004 mol L⁻¹ min⁻¹ = k[6 × 10⁻² molL⁻¹ ]^α [1 × 10⁻² molL⁻¹ ]^β ...(a) 

0.008 molL⁻¹ min⁻¹ = k[6 × 10⁻² molL⁻¹ ]^α [2 × 10⁻² molL⁻¹ ]^β ...(b)

Dividing eqⁿ (b) by (a)

Similarly from observations (i) and (iii)

Order of reaction n = a + b = 2

∴ Rate law for reaction is 

Rate = k [A] [B] 

From observation (i)

0.004mol L⁻¹ min⁻¹ = k[6 × 10⁻² mol L⁻¹ ] [1 × 10⁻² mol L⁻¹ ]