Reactions in Flames:

The most significant reactions occurring within the flame are given below.

i) Dissociation of molecules

MX   → M + X, K_mx = P_m P_x/P_mx

ii) Creation of compounds along with flame components

M + Y → MY, K_my = P_m P_y /P_my

iii) Ionisation of atoms

M→M⁺ +e^-, K_p=P⁺_m+ P^-_e-/P_m

In the above equations, p is the partial pressure of the species implies in the subscript. The partial pressure of the flame gas elements is much larger than the partial pressure of the given components. It is, thus, considered constant and involved within the equilibrium constant.

The most significant of the flame gas elements forming compounds along with the elements are oxygen, the hydrogen and hydroxyl radical. The most general compounds created in flames burning along with air or oxygen and metal monoxides. For instance, a main fraction of alkaline earth elements is present as monoxides unless extremely fuel rich flames are used. Therefore, alkali metals practically do not form any oxides.

Hydroxide species are present for a few alkali and alkaline earth elements within hydrocarbon flames. Sodium forms practically no hydroxide, although the concentration of LiOH molecules frequent exceeds the atomic lithium concentration through a factor of 10. No one of the alkali metal hydroxides emit spectral bands within the visible or UV region; while the spectral bands of alkaline earth monohydroxide could be used for the determination of these elements.