During industrial fuel gas manufacture, passing steam over incandescent coke yields water gas, whereas passing air over red-hot coke produces producer gas. Which of the following statements correctly explains why water gas possesses a significantly higher calorific value per unit volume than producer gas?
- Water gas consists entirely of combustible gases ( and ), whereas producer gas contains a high percentage of non-combustible nitrogen () from air.Answer
- BThe synthesis of water gas is an exothermic reaction that traps excess chemical enthalpy directly inside the resulting gas molecules.
- CProducer gas primarily consists of carbon(IV) oxide () and steam (), which impede active combustion.
- DWater gas contains high concentrations of hydrocarbon allotropes of carbon that release double the combustion energy of carbon(II) oxide.
Answer
Water gas possesses a higher calorific value because both of its major constituents, carbon(II) oxide () and hydrogen (), are flammable fuel gases. In contrast, producer gas contains approximately atmospheric nitrogen (), an inert, non-combustible gas that dilutes the energy density.
Water gas is synthesized by passing steam over incandescent coke at around , producing an equimolar mixture of carbon(II) oxide and hydrogen gas (). Since both constituent gases burn in air releasing substantial heat, of the gas volume is combustible. Producer gas, made by passing air over red-hot coke (), contains nearly atmospheric nitrogen by volume. Nitrogen is non-combustible and absorbs heat during combustion, resulting in a substantially lower calorific value for producer gas.
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Key Concept
Industrial Fuel Gas Compositions and Calorific Values
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