Consider the data presented below. time (s) 0 40 80 120 160 moles of a 0.100 0.067 0.045 0.030 0.020 part a part complete determ
ine whether the reaction is first order or second order. determine whether the reaction is first order or second order. this is the first order reaction. this is the second order reaction. submitprevious answers correct part b what is the rate constant?
To determine which order of the reaction it is, first we need to calculate the rate of change of moles. the data is as follows time 0 40 80 120 160 moles 0.100 0.067 0.045 0.030 0.020
Q1) for the first 40 s change of moles ; = -d[A] / t = - (0.067-0.100)/40s = 8.25 x 10⁻⁴ mol/s for the next 40 s = -(0.045-0.067)/40 = 5.5 x 10⁻⁴ mol/s the 40 s after that = -(0.030-0.045)/40 s = 3.75 x 10⁻⁴ mol/s k - rate constant and A is the only reactant that affects the rate of the reaction
rate = k [A]ᵇ 8.25 × 10⁻⁴ mol/s = k [0.100 mol]ᵇ ----1 5.5 x 10⁻⁴ mol/s = k [0.067 mol]ᵇ -----2 divide the 2nd equation by the 1st equation 1.5 = [1.49]ᵇ b is almost equal to 1 Therefore this is a first order reaction
Q2) to find out the rate constant(k), we have to first state the equation for a first order reaction. rate = k[A]ᵇ As A is the only reactant thats considered for the rate equation. Since this is a first order reaction, b = 1 therefore the reaction is rate = k[A] substituting the values, 8.25 x 10⁻⁴ mol/s = k [0.100 mol] k = 8.25 x 10⁻⁴ mol/s /0.100mol = 8.25 x 10⁻³ s⁻¹
