In the formation of sulphur trioxide by the contact process. 2SO2(g)+O2(g)⇌2SO2(g) The rate of reaction is expressed as −d(O2)dt=2.5×10−4molL−1s−1 The rate of disappearance of (SO2) will be:
2SO2(g)+O2(g)⇌2SO2(g)
Rate=−d[SO2]2dt=−d[O2]dt
∴=−d[SO2]dt=2×−d[O2]dt
=2×2/5×10−4
=5.0×10−4mol−4mol−1L−1s−1