AQA A Level Chemistry Electrochemical Cells

Why would removing the voltmeter and replacing it with a lamp or ammeter allow the reaction to go to completion please?

Voltmeters have very high resistances, so the current passing through the circuit isn’t sufficient to allow the reaction to go to completion.

Replacing the voltmeter with a component with a much lower resistance, i.e a lamp, does allow a sufficient current to pass through the circuit.

Reply 2

GeT_iN_SHinJI

A voltmeter is used to measure the maximum possible potential difference. This is because voltmeters have a high level of resistance so stop the current from flowing in the circuit, allowing the maximum possible potential difference to be measured. The prevention of current from flowing means that the reactions at each electrode no longer occur. When the voltmeter is removed and replaced with a bulb/ammeter, the current flows and the reactions occur separately at each electrode and the reactants are used up.