This includes exothermic and endothermic reactions.
Exothermic: Reactions that release heat
Endothermic: Reactions that absorb heat
Heat is just a form of energy and all chemicals have stored energy. Stored energy is called Enthalpy.
Enthalpy is a chemical potential energy.
Exothermic Reactions convert enthalpy into heat.
2C8H18 + 25O2 ---> 18H2O + 16CO2 + Heat
Enthalpy is given the symbol H, hence Delta H is change in enthalpy.
Here is an image of how an enthalpy diagram looks like:
Exothermic Diagrams shows high to low enthalpy, change in enthalpy is negative and heat is released. While endothermic diagrams show the opposite of exothermic diagrams.Endothermic diagrams shows low to high enthalpy, change in enthalpy is positive and heat is absorbed.
II. Change in Enthalpy and Moles
Coefficients can stand for moles or molecules
N2 + 3H ---> 2NH3 + 46.3 kJ
1 mole of N2 ==> 46.3 kJ
3 moles of H2 ==> 46.3 kJ
2 moles of NH3 ==> 46.3 kJ
Conversion Factors
46.3 kJ/1 mol N2 , 46.3 kJ/3 mol H2 , 46.3 kJ/ 2 mol NH3
Now, here are some examples.
1. Fin the amount of heat produced if 6.0 mol of H2 are consumed when making ammonia.
6.0 mol x 46.3 kJ/3 mol of H2 = 92.6 kJ