Knowing how fast a reaction proceeds is essential in designing manufacturing plants or considering the economics of industrial processes. It also gives evidence about the mechanism of a chemical reaction. The initial rate of a chemical reaction can be obtained from the slope of a tangent of a concentration-time graph drawn at t=0 seconds. For reactions involving acids or bases titrations or a pH meter can be used to measure changes in pH with time. For reactions that produce gases the change in volume or pressure or loss in mass can be measured. For reactions where there is a colour change colorimetry can be used to follow the changes. For reactions where there is a precipitate formed the time taken for a mark on a white tile to disappear can be measured. The results for the decomposition of sulfuryl chloride are shownSO2Cl2 (g) → SO2(g) + Cl2(g)