The partial burning of coal in the presence of O2 and H2O produces a mixture of
ID: 963796 • Letter: T
Question
The partial burning of coal in the presence of O2 and H2O produces a mixture of CO(g) and H2(g) called synthesis gas. This gas can be used to synthesize organic compounds, or it can be burned as a fuel. A typical synthesis gas consists of 55.0% CO(g), 33.0% H2(g) and 12.0% noncombustible gases (mostly CO2(g)), by volume. What volume of the synthesis gas, measured at STP and burned in an open flame (constant-pressure process), is required to heat 40.0 gal of water from 15.8 to 65.0 C? (1gal=3.785L.)
Explanation / Answer
Calculations;
Heat produced by combustion of combustible gases ( ie. CO & H2 in one mole of synthesis gas =
( heat of combustion of CO(g) x mole % + enthalpy of combustion of H2 (g) x mole % )
= ( 283 x 0.55 ) + ( 285.8 x 0.33 )
= 249.96 kJ
Heat produced by combustion of one mole of synthesis gas =
heat liberated by combustion of combustible matter ( ie. CO & H2 ) - ( heat taken up by
incombustible matter ( ie. mostly CO2 ) in the gas )
.........................................................= ( 254.96 - 254.96 x 0.12 )
..........................................................= 234.60 k J
heat required to raise the temperature of 40 gallons { ( or = 40 x 3.785 ) litres } water
from 15.8o C to 65o C = { 40 x 3.785 x (65 - 15.8 ) } kCal.
....................................= 7448.80 kCal.
.................................... = 31186.64 k J
therefore volume of synthesis gas required to heat 40 gallons of water from
18.5oC to 65o C = {(31186.64 / 234.60 ) x 22.71098 litres }
.......................... = 3019.09 Litres at STP
Note ;
(i)....Volume % is directly proportional to mole percent ,as per Avagadro's law.
(ii)... one mole of any gas at STP occupies 22.71098 litres
(iii)... Enthalpy of combustion for H2 & CO gases are as per reactions-
......................H2 (g) + 1/2 O2 (g) -----------> H2 O delta Ho = -285kJ mol-1
.....................CO (g) + 1/2 O2 (g) ----------> CO2 delta Ho = -283 kJ mol-1
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