[Lynda92]

Why is a high resistance voltmeter used when measuring the potentials in electrochemical cells?

I've read it's used to reduce current flow through the wires but, wouldn't this stop electron flow and therefore prevent the redox reaction occurring?


Some help understanding this would be much appreciated.

[mjc123]

It is not necessary for current to flow and the reaction to proceed to any significant extent in order to measure the potential. Even if there were no connecting wire and no current flowed, there would still be a potential difference between the zinc and copper electrodes. That is what you are measuring with the voltmeter. If there were a significant current, the potential would be reduced by an amount IR_e, where R_e is the internal resistance of the cell.

[Enthalpy]

"High resistance" must be a tradition from the time of coil-and-magnet voltmeters. Presently they're electronic, and you wouldn't find one with less than 1Mohm input resistance, and 10 to 100Mohm is more common, so with usual concentrations, pretty much any voltmeter fits.