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chemistry igcse acapprinted 77 · PDF 77
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77
Oxides of Nitrogen and Catalytic Converters
Nitrogen oxides (NO and NO₂) are produced when nitrogen and oxygen react under the high
pressure and temperature conditions of internal combustion engines and blast furnaces. Exhaust
gases also contain unburned hydrocarbons and carbon monoxide. To neutralize these harmful
emissions, cars are equipped with catalytic converters as part of their exhaust systems.
Catalytic converters contain catalysts made from transition metals, such as platinum and rhodium,
arranged in a honeycomb structure to maximise the surface area for reactions. Through a series of
redox reactions, these catalysts neutralize pollutant gases. For instance, carbon monoxide is
oxidized to form carbon dioxide: 2CO + O₂ → 2CO₂.
Nitrogen oxides are reduced to nitrogen gas: 2NO → N₂ + O₂ and 2NO₂ → N₂ + 2O₂.
A single reaction that represents the interaction of nitrogen monoxide and carbon monoxide
within a catalytic converter is: 2NO + 2CO → N₂ + 2CO₂.
Photosynthesis
Photosynthesis is an endothermic reaction in which energy is absorbed from the environment by
chloroplasts containing chlorophyll. In this process, carbon dioxide and water act as reactants and
are converted into glucose and oxygen. Chlorophyll and light energy are essential for this reaction
to take place. Following is the equation for the process:
Carbon Dioxide + Water → Glucose + Oxygen
6CO2 + 6H2O → C6H12O6 + 6O2
P2:
Q1. How do carbon dioxide and methane cause global warming?
They emit the thermal energy they have absorbed back to the Earth.
They absorb the radiation directly from the Sun.
They increase thermal energy loss to space.
They reduce reflection of thermal energy from the Earth’s surface.