Can It Be Chemical ?

Often, the main argument of skeptics about excess heat measurement in LENR experiments is that is could be chemical.

So let's dig into the subject, now that we know we can have 71 mg of dihydrogen in the cell.

Let's assume we also have O2 oxygen in the cell and that the reaction is producing H2O from H2 and O2.
This is one of the most exothermic chemical reaction known. It is used to send rockets to the Moon or to Mars.

At 298°K, the bond energies involved are (note that depending on the book, the values can slightly vary):

H-H:   436 kJ/mol
O=O: 495 kJ/mol
H-O-H:   493.5 + 424.4 = 918 kJ/mol

To produce 1 mole of water from 1 mole of H2 and half a mole of O2, the H-H single bond and the O=O dual bond needs to be broken.

Energy to make monoatomic H and O: 436 + 495/2 = 683.5 kJ / mol
Bond energy stored in H2O molecule : 918 kJ/mol
Energy produced: 918 - 683.5 = 234.5 kJ per mole of H2O

As we need 1 mole of H2 to produce 1 mole of H2O and as we have at maximum 0.0352 mole of H2 in the cell,
the maximum chemical energy we can produce is: 0.0352 * 234.5 = 8.25 kJ

However as we do not have O2 in the cell, the best source of oxygen is in the SiO2 of the glass:

Si-O: 368 kJ/mol

Energy to make monoatomic H and O: 436 + 368 = 804 kJ / mol
Bond energy stored in H2O molecule : 918 kJ/mol
Energy produced: 918 - 804 = 114 kJ per mole of H2O

Chemical energy in the cell: 0.0352 * 114 = 4.01 kJ

Even, in very hypothetic worst case scenario, 8.25 kJ corresponds to only 2.29 W·h
And this would mean that the cell pressure would go from 3.5 bars to 0.0 bar while consuming all hydrogen molecules in the cell.
However, this calculation is an approximation using bond energy at ambient temperature. Both temperature and pressure in the cell are affecting the bond energies, but the orders of magnitude are correct.
More details can be found here: Water’s Hydrogen Bond Strength

In conclusion, with our cell, any excess power above 1 watt during multiple hours cannot be chemical.