Activation Enthalpy (Setting stuff on fire)

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.

Notes:

·         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.