2.24 The following reactions might be used to power rockets: (1) H2(g)+21O2(g)=H2O(g) (2) CH3OH(l)+121O2(g)=CO2(g)+2H2O(g) (3) H2(g)+F2(g)=2HF(g) (a) Calculate the enthalpy changes at 25C for each of these reactions per kilogram of reactants. (b) Since the thrust is greater when the molar mass of the exhaust gas is lower, divide the heat per kilogram by the molar mass of the product (or the average molar mass in the case of reaction 2) and arrange the above reactions in order of effectiveness on the basis of thrust. fHm(H2O,g)=241.818kJmol1fHm(HF,g)=271.1kJmol1fHm(CH3OH,1)=238.66kJmol1fHm(CO2,g)=393.509kJmol1 2.24 The following reactions might be used to power rockets: (1) H2(g)+21O2(g)=H2O(g) (2) CH3OH(l)+121O2(g)=CO2(g)+2H2O(g) (3) H2(g)+F2(g)=2HF(g) (a) Calculate the enthalpy changes at 25C for each of these reactions per kilogram of reactants. (b) Since the thrust is greater when the molar mass of the exhaust gas is lower, divide the heat per kilogram by the molar mass of the product (or the average molar mass in the case of reaction 2) and arrange the above reactions in order of effectiveness on the basis of thrust. fHm(H2O,g)=241.818kJmol1fHm(HF,g)=271.1kJmol1fHm(CH3OH,1)=238.66kJmol1fHm(CO2,g)=393.509kJmol1