Question

What is the average reaction rate for 2 NOBr(g) --> Br2(g) + 2 NO(g) over the first 10 seconds? Time (s) [NOBr] (mol/L) 0.00 0.0100 2.00 0.0071 4.00 0.0055 6.00 0.0045 8.00 0.0038 10.00 0.0033

Answer 1

Average rate is just an approximate value of the reaction rate in the given time interval; it does not necessarily mean that the reaction has this "specific rate" throughout the time interval or even at any instant during that time.

Average rate (Δ[conc.] / Δt) = (Change in the concentration of reactants or Products) / time

For 2 NOBr(g) --> Br₂(g) + 2NO(g) reaction :

Average rate= - [NOBr]/ t (-ve sign for consumption of reactants, to make the rate a positive number)

We need to calculate the average rate over the first 10 seconds,

Concentration of NOBr at 0 s = 0.0100 mol/L

Concentration of NOBr at 10 s = 0.0033 mol/L

Change in Concentration of NOBr over 10 secs = -[0.0033 mol/L- 0.0100 mol/L)/ (10-0)] = 0.0067/10= 0.00067

Average rate of reaction = 6.7* 10^-4 mol L^-1 s^-1