Question

The ozone layer is a protective layer around the Earth that absorbs UV radiations. Stratospheric ozone is depleted through the reaction of ozone, O3O3, with nitric oxide, NONO. The gaseous emissions from vehicles and industries are responsible for the rapid destruction of this layer. The destruction of the ozone by nitric oxide (NONO) is shown in the video. This is a two-step reaction, called a multistep reaction, involving a catalyst and an intermediate. Nitric oxide (NONO) enhances the reaction rate, and thus it acts as a catalyst, whereas NO2NO2 (nitrogen dioxide) is an intermediate not present in the chemical equation of the overall process.

Part A

The video demonstrates how stratospheric ozone is depleted by the reaction of ozone with trace constituents of the stratosphere. Complete the catalytic destruction reaction of ozone when it reacts with a catalyst. Reaction 3 is the net overall reaction when reactions 1 and 2 are added.

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O2O2

O Subscript2

O3O3

O Subscript3

OO

O

2O22O2

2 O Subscript2

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Multistep reactions: Catalysts and intermediates

In multistep reactions, usually some of the substances are consumed in the reaction, and some are regenerated. A substance that is consumed in the first step and is regenerated in the next is a catalyst. In contrast, when a substance is formed in the first step and is consumed in the next step, then it is known as an intermediate.

Part B

Chlorine released from chlorofluorocarbons (CFCs) reacts with ozone in the atmosphere to form oxygen. The proposed reactions are

1. Cl(g)+O3(g)→ClO(g)+O2(g)Cl(g)+O3(g)→ClO(g)+O2(g)
2. ClO(g)+O(g)→Cl(g)+O2(g)ClO(g)+O(g)→Cl(g)+O2(g)

Identify the species that acts as a catalyst and the one that acts as an intermediate in these reactions.

Express your answers as chemical formulas separated by a comma.

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catalyst, intermediate =

nothing

Answer 1

Part a

Reaction 1

NO + O₃ = NO₂ + O₂

Reaction 2

NO₂ + O = NO + O₂

Reaction 1 + Reaction 2 = Reaction 3

O₃ + O = 2O₂

Part b

1.Cl(g)+O₃(g)→ClO(g)+O₂(g)

2.ClO(g)+O(g)→Cl(g)+O₂(g)

Net reaction can be obtained by adding the above reaction

O₃ + O = 2O₂

Catalyst occurs in the initial reaction and found in the final step as it as because it doesn't take part in the reaction

Catalyst = Cl(g)

Intermediate will form and disappear at the final stage

Intermediate = ClO(g)

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