X is endothermic because the energy produced is lower than the energy of the reactants added.
Y is exothermic because the energy produced supersedes the energy of the reactant added.
· We add activation enthalpy to fuel to break bonds, creating new product.
· If we get more energy than we put in, reaction is exothermic, which is good in the case of fuels.
· The reactant energy required is whatever energy is required to break the bonds in the solution/fuel. For example, in the case of Methane:
Methane reaction formulae:
CH4 + 2O2 à CO2 + 2H2O
4 C-H bonds + 2 O=O bonds à 2 C=O bonds + 4 H-O bonds
4(414) + 2(498) à 2(720) +4(464)
Previously knowing that:
C-H bonds require 414 K.joules mole-1 to break/make.
O=O bonds require 498 K.joules mole-1 to break/make.
C=O bonds require 720 K.joules mole-1 to break/make.
O-H bonds require 464 K.joules mole-1 to break/make.
Which results in:
2652 K.joules mole-1 à 3296 K.joules mole-1
Meaning, the reaction of reacting Methane with Oxygen is exothermic.