Hess's Law

some properties of enthalpy

 

 

 

 

 

 

 

 

 

 

 

Standard States:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Example: Find the value of DeltaH for the reaction:

2 CO2 + 7 H2 right arrow C2H6 + 4 H2O(g)

From Table find DeltaH values:

Often just list compounds, since known to be from elements.
 C + O2 right arrow CO2  DeltaH = -393.5 kJ mol-1
 2 C + 3 H2 right arrow C2H6  DeltaH = -84.6 kJ mol-1
H2 + 1/2 O2 right arrow H2O(g)  DeltaH = -241.8 kJ mol-1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

EM_Spectra_image

public domain image from Louis E. Keiner via Wikipedia Creative Commons

 

 

 

© R A Paselk

Last modified 8 March 2013