For the decomposition of hydrogen iodide on a gold surface

Question

For the decomposition of hydrogen iodide on a gold surface at 150 °C

2 HI(g)H₂(g) + I₂(g)

the average rate of disappearance of HI over the time period from t = 0 s to t = 1019 s is found to be 1.20×10^-4 M s^-1. 

The average rate of formation of I₂ over the same time period is  M s^-1