Chemistry help.....

Question

Hydrogen saving is done by producing hydrogen from water with solar energy.The gas produced then burnt as the fuel:2H2 (g)+O2(g)>2H2O (l).The main advantage of hydrogen as fuel is not causing pollution.The biggest disadvantage is gas form of this fuel makes difficult to store compared to liquid or solid.What is the volume of hydrogen on temperature of 25C and 1.00 arm to produce energy that equivalent to energy produced from combustion of one gallon octane (C8H18).Octane density is 2.66 kg/gallon with standard formation enthalpy of 249.9 J/mol.

A.1.09*10^4 L
B.12.9*10^3 L
C.1.09*10^3 L
D.3.41*10^4 L
E.3.41*10^3 L

Answer 1

To solve this problem, determine the total  heat energy obtained by burning 2.66 kg of octane.  Then divide the value by the heat of formation of water to obtain the number of moles of hydrogen required to produce the same energy.  Then multiply the value by 22.4 L/mol.

 

Enthalpy of formation for liquid water is -285.8 kJ/mol

Enthalpy of formation for gaseous water is -241.8 kJ/mol  (presumably, this is the value used for this problem)

Enthalpy of formation for n-octane is -249.95 kJ/mol

Enthalpy of formation for CO₂ is -393.5 kJ/mol

 

H₂ + 1/2O₂ --> H₂O

 

C₈H₁₈ + 25/2O₂ --> 8CO₂ + 9H₂O

ΔH_rxn = 8(-393.5) + 9(-241.8) - (-249.95) = -5074 kJ

 

mol_octane = 2660g (1 mol_octane /114.228 g) = 23.3 mol

 

Heat produced by burning 23.3 mol of octane = 23.3 mol (5074 kJ/mol) = 118000 kJ

 

mol hydrogen = 118000 kJ / 241.8 kJ = 488 mol

L hydrogen = 448 mol (22.4 L / mol) = 1.09 x 10⁴ L H₂