Question

Photochemical reaction of h2 and cl2 over water surface is which order

Answer 1

Reaction between hydrogen and chlorine under the influence of UV light is the photochemical combination of hydrogen and chlorine. The reaction does not take place in dark. This is a zero- order reaction as the rate is independent of the concentration of both hydrogen and chlorine. The rate of reaction is investigated by placing the hydrogen and chlorine gases in a closed glass vessel containing calculated amount of water which can dissolve the product, HCl. H2 + Cl2 ---> 2 HCl

Initiation: Cl2 + hv ---> 2 Cl ·

Propagation: Cl · + H2 ---> HCl + H· ;

H· + Cl2 ---> HCl + Cl ·

Termination: 2 H· ---> H2

2 Cl · ---> Cl2

H· + Cl · ---> HCl

The enthalpy for the initiation step is 243.36 kJ per mole of Cl2 which corresponds to the energy carried by light photons toward the violet end of the visible spectrum with a wavelength of 491.5 nm

The reaction uses hydrogen and chlorine which does not dissolve in water and when HCl is formed which dissolve in water, so the water level rises in the vessel. The rise in the water level is directly related to the rate of the reaction. The concentration of gases in unit volume above the surface of water in the vessel always remain constant because of rise in water level although their quantities are decreasing gradually. Hence the rate of reaction remains constant as the rate is related to the rate of disappearance of hydrogen and chlorine.

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Answer 2

Photochemical reaction of $H2$ and $Cl2$ over water surface is a zero order reaction.

Explanation:

• The Photochemical reaction between hydrogen and chlorine $H2 + Cl2 ----- 2HCl$
• This photochemical reaction is a zero order reaction.
• The reaction is carried out between hydrogen and chlorine which is placed over the water surface.
• The rate of reaction is estimated with the rise in water level due to the formation of hydrogen chloride.
• The rate of rising is equal to the rate of disppearance of hydrogen and chlorine.

• The concentration of gases per unit volume will not change with time.