Stage 2 Chemistry, Unit 1.2- Monitoring the Environment- Photochemical smog and catalytic converters

Year 12 Stage 2 Chemistry

How much percent of the atmosphere does oxygen make up?

21%

How much of the atmosphere does nitrogen make up?

78%

Nitrogen N₂ is

a diatomic molecule (with a triple covalent bond)

Nitrogen takes

a large amount of energy to break its triple bond

When nitrogen’s triple bond is broken, it forms

nitric oxide N₂ +O₂→ 2NO

what are some natural causes for the breaking of nitrogen’s triple bond?

Lightning, bushfires, volcanic activity

What are some anthropogenic causes of the breaking of nitrogen’s triple bond?

Internal combustion engines

Jet Engines

Industrial kilns and furnaces

What is the lowest layer of the atmosphere called?

the troposphere

(it is the most effected by human activity

75% of gases present in the atmosphere are found in:

the troposphere

What is photochemical smog?

mixture of pollutants, directly from the source and from secondary reactions, that causes a hazy smog, which can cause respiratory issues and heat inversion

What does photochemical smog contain?

VOC, NO_X and O₃

What does VOC stand for?

Volitile organic compound

What are the characteristics of a VOC?

VOCs are usually small unburnt organic compounds. becuase they are small, there are present as gases at room temperature, which attributes to their name

How do O₃ and NO₂ effect photochemical smog?

Nitrogen dioxide gives the smog a brown haze.

What causes the O₃ and NO₂ in photochemical smog?

Emissions from motor vehicles are the main contributor to photochemical smog’s formation. Incomplete combustion occurs in the enginges, leading to the creation of undesirable products, such as VOCs, Carbon monOxide and carbon.

When emitted from a car, nitrogen reacts with oxygen to form

nitrogen/ nitric oxide( N₂ +O₂→ 2NO)

When do Nitrogen oxide/Nitric oxide percentages peak during the day?

They peak early in the morning.

After peaking in concentration, Nitric oxide/ nitrogen oxide is further oxidised to form

nitrogen dioxide ( 2NO+O₂→ 2NO₂ )

NO₂ levels peak

After the levels of NO.

When does NO₂ dissociate to make an oxygen radical

At noon, as the UV levels are at their highest, as sunlight acts as a catalyst, allowing for the reaction to take place.

During noon, the oxygen

combines with an O₂ to form trophospheric ozone (O₃). This reaction peaks after midday.

What are some effects of photochemical smog for humans and animals?

pollutants can cause eye irritations and respiratory distress.

Eye fluid can react with pollutants to form nitric acid.

while O₃ can react to respiratory tissue and reducing the amount of oxygen that can be absorbed in the lungs.

What are some effects of photochemical smog for Plants and Vegetation

Exposure to Ozone present in photochemical smog can cause plant' stomata and leaves to close, limiting the gases exchanged for photosynthesis therefore photosynthesis itself. this distrupts plant growth and makes plants more susceptible to disease.

What are some effects of photochemical smog on industrial systems

Elastic polymers (elastomers) are made brittle by ozone, as ozone breaks the carbon-carbon double bonds in the chains, called degradation, which makes smaller chain molecules, weakening their overall strength due to the decrease in dispersion force (due to size). This also causes weaker interactions between chains.

What are Catalytic converters?

Catalytic converters are present mainly in a vehicles exhaust system, reducing harmful emissions.

What is a catalytic converter made of?

Catalyst support/ substrate, a wash coat and a catalyst.

What is a Substrate (catalyst support) in a three way catalytic converter?

A substratee is usually a ceramic block, which has a honeycomb structure, allowing for a higher surface area for reactions to occur.

What is a Wash coat in a three way catalytic converter?

A wash coat covers the substrate, and further increases the surface area. The wash coat usually contains alumina, as it helps disperse catalytic metals.

What is a catalyst in a three way catalytic converter?

The catalyst is made from materials such as platinum, palladium and rhodium, and causes the harmful chemicals to react into less harmful chemicals.

What does Platinum (Pt) cause in a catalytic converter?

Platinum is utilised for both oxidation and reduction, converting carbon monoxide (CO) into carbon dioxide (CO2) and hydrocarbons (HC) into water (H2O) and CO2

2C₈H₁₈+25O₂ → 16CO₂+18H₂O

What does Palladium (Pd) cause in a catalytic converter?

Palladium is used for oxidation reactions, to convert hydrocarbons and carbon monoxide into less harmful chemicals.

2CO+ O₂ → 2CO₂

What does Rhodium (Rh) cause in a catalytic converter?

Rhodum is utilised for reduction, reducing NO_x into N₂ and O₂

2NO+2CO → 2CO₂ +N₂