Engineering Thermodynamics
A closed system is one in which

Mass crosses the boundary but not the energy
Mass does not cross boundaries of the system, though energy may do so
Both energy and mass cross the boundaries of the system
Neither mass nor energy crosses the boundaries of the system

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Engineering Thermodynamics
Mond gas is obtained by

Carbonisation of bituminous coal
Passing steam over incandescent coke
Partial combustion of coal, coke, anthracite coal or charcoal in a mixed air steam blast
Passing air and a large amount of steam over waste coal at about 650°C

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