The thermochemical equation for the dissociation of hydrogen gas into atoms may

Question

                    The thermochemical equation for the dissociation of hydrogen gas into atoms may be written:                 

                    H2 > 2H     ,   H=1824.2 kJ                 

                    What is the ratio of the energy yield on combustion of hydrogen atoms to steam to the yield on combustion of an equal mass of hydrogen molescules to steam                     given : 2H2(g) + O2(g) > 2H2O(g) H= -2023.7kJ                 

                                     must show work

Explanation / Answer

H2 > 2H , Hhydrogen=1824.2 kJ

2H2(g) + O2(g) > 2H2O(g) H= -2023.7kJ

In the second reaction 2 moles of H2 react dividing the whole reaction by 2 the enthalpty for the new reaction

Hnew = H/2 = -2023.7/2 = -1011.85 KJ

Ratio of energy yield = Hydrogen/Hsteam = 1824.2/1011.85 = 1.8

The energy yield for Hydrogen atoms is 1.8 more than that of steam when same mass of Hydrogen is used

This is the reason why Hydrogen is used as a fuel in Rockets and not steam

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