How could you determine the amount of hydrogen needed for a space flight

The principle is that you use magnetic fields to collect and concentrate hydrogen atoms from the near vacuum of space, and then a fusion rocket would turn some of this into propulsion for speed and a fusion reactor would convert the some into power to maintain the fields. The rest would get stored in tanks.

the potential energy of the reactants is 200j.

from the energy diagram, the energy of the product formed is 350j; this means that, this reaction is an endothermic reaction, because it absorbs energy from its environment.

c (diamond),

sio2 (quartz)