This post begins a series of examples from my reactor modeling book. The examples in the book are too large for a blog post, so I will break them down into smaller pieces.
This first post will show how the temperature dependent heat of reaction is obtained from the heats of formation and heat capacities.
Steam reforming of methane will be used as the example system.
CH4 + H2O <--> CO + 3 H2 Reaction 0
CO + H2O <--> CO2 + H2 Reaction 1
The components will be referred to in the order below:
The stoichiometric matrix for the system is given by:
where rows are for reactions and columns are for species.
Heat of Formation
The heats of formation at a standard state (T = 298 K, ideal gas) are needed. These may be obtained from reference tables or from a physical property program such as Prode Physical Properties (PPP). The values below were obtained from PPP. The PPP values are on a weight basis, so they have been multiplied by molecular weights to convert to a molar basis.
Enthalpy as a function of temperature
The above function produces a vector of the molar enthalpies.
Heats of Reaction
Finally, the heats of reaction are obtained using the stoichiometric matrix.
The plot shows that an assumption of constant heat of reaction in the reaction range would be valid for this system.