PLEASE HELP I AM SO CONFUSED

Question

A space shuttle uses more than one type of rocket fuel. The two solid rocket boosters use a fuel mixture of aluminum and ammonium perchlorate (together they form the solid fuel) that reacts according to the equation

3Al(s) + 3NH4ClO4(s) = Al2O3(s) + 3NO(g) + 6H2O(g) + AlCl3(s)

In the three main shuttle engines, a mixture of hydrogen and oxygen form a second fuel. The hydrogen and oxygen are carried as compressed liquids in a large tank adjoining the shuttle and react to produce energy according to the reaction

H2(g) + 1/2O2(g) = H2O(g)

∆fH° of NH4ClO4(s) = −295.3 kJ/mol

∆fH° of AlCl3(s) = −705.6 kJ/mol

Compare the two rocket fuels as energy sources for powering the space shuttle by finding the enthalpy change

for each reaction.

Your response should also include

an analysis of the energy to mass ratio (kJ/g) for each fuel.

• What is the significance of this value?

an environmental concern or benefit related to each fuel

Answer 1

The enthalpy change of the reaction can be found as follows: [(product A enthalpy of formation x moles of product A) + (product B enthalpy of formation x moles of product B) + ...] - [(reactant A enthalpy of formation x moles of reactant A) + (reactant B enthalpy of formation x moles of reactant B) + ...]. It is critical that you distribute the minus sign throughout the whole second set of brackets. The first fuel's reaction enthalpy can be calculated using the formula above. Some enthalpies of formation (delta Hf) are listed for the first reaction, but it appears that you'll have to look up the values for the other compounds. The reaction enthalpy of the second fuel is just the enthalpy of formation of water times your number of moles of water since it is forming directly from elemental hydrogen and oxygen. A negative enthalpy change is exothermic (system releases energy into surroundings), while positive change is endothermic (system absorbs energy from surroundings). A very exothermic reaction releases a lot of heat, which can be dangerous, certainly more than a more endothermic reaction. That should get you on the right track.