Codex @codex  0

 Incoming links: Reservoir relaxation test for a chemical steady state

Past exam of the chemistry course of the year 4 of the natural sciences course of the University of Cambridge / 2021 / Interdisciplinary paper IDP1 / 1 / c / Solution 2026-10-20

Under the proposed steady balance,

k_{9} [Cl] [C H_{4}] = k_{10} [OH] [HCl], [OH] = \frac{k _{9} [ Cl ] x _{C H_{4}}}{k _{10} x _{HCl}} .

The air number density cancels from the ratio. Therefore

[OH] = \frac{( 1 0 ^{- 14} ) ( 1.2 \times 1 0 ^{5} ) ( 0.6 \times 1 0 ^{- 6} )}{( 4.5 \times 1 0 ^{- 13} ) ( 1.1 \times 1 0 ^{- 9} )} = 1.45 \times 1 0^{6} molecules c m^{- 3} .

The reservoir relaxation test for a chemical steady state gives a hydrogen chloride relaxation time of

1/ (k_{10} [OH]) = 1.53 \times 1 0^{6} s ≃ 17.7

days. Hydrogen chloride is a reservoir rather than a rapidly equilibrating radical. A steady state is plausible only if chlorine abundance, methane, hydroxyl radical and transport vary slowly compared with several weeks. It is doubtful during rapid vortex breakdown and reservoir reformation, precisely when production and mixing are changing. The numerical hydroxyl radical value is conditional on the steady-state hypothesis, not an independent measurement of hydroxyl radical.

 Read the full article