Does the electrochemical series ranking of half cells stay constant even in non standard conditions?
Nope. Using the Nernst equation (google it; gives you altered cell potentials at non-standard conditions), one finds that for a given reaction quotient Q (which measures how non-standard your half-cell is), the deviation of the cell potential from standard potentials depends on how many electrons are involved per half reaction. So, the oxidation of silver to silver(I) is going to be affected more than the oxidation of copper to copper (II).
In physical terms, a deviation from standard conditions produces an energy imbalance in the half-cell, so to speak. Voltage is energy per unit charge; think of it as distributing the chemical energy, in this case, over the charges that will use it. If you have more electrons involved in the reaction, the energy imbalance is shared over more electrons, and thus the change in the voltage from standard conditions decreases in magnitude.
Not exactly. The energy associated with intermolecular bonds is much lower than that of intramolecular forces. It still contributes a little bit but the main thing here is that methanol and ethanol are partially oxidised forms of methane and ethane, so some of that energy that has already left the system. A better way to explain it is that ethanoic acid (acetic acid) has a lower heat of combustion than ethanol, because it has already been partially oxidised (we know this through oxidation using permanganate or dichromate).
This is correct, but it would be stronger to explain why this partial oxidation reduces the energy available for combustion. In this case, it's because the energy from combustion comes from splitting C-H, C-C, O=O bonds to form C=O, O-H bonds. If you already have C-O bonds in your fuel, that means you form less C-O bonds and thus less energy is produced.
(If you want an explanation of why C=O, O-H bonds are more stable, consider polarities of the bonds and electronegativities of the atoms)
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