Chemistry » Introducing Electrochemical Reactions » The Effects Of Current And Potential On Rate And Equilibrium

Current and Rate of Reaction

Current and rate of reaction

A galvanic cell

Let’s think back to the \(\text{Zn}\)-\(\text{Cu}(\text{s})\) electrochemical cell. This cell is made up of two half-cells and the reactions that take place at each of the electrodes are as follows:

\(\color{blue}{\text{Zn(s)} \to \text{Zn}^{2+}\text{(aq) + 2e}^{-}}\)

\(\color{red}{\text{Cu}^{2+}\text{(aq) + 2e}^{-} \to \text{Cu(s)}}\)

  • At the zinc electrode, the zinc metal loses electrons and forms \(\text{Zn}^{2+}\) ions. The electrons are concentrated on the zinc metal while the \(\text{Zn}^{2+}\) ions are in solution.

  • At the copper electrode, the copper ions gain electrons and forms solid copper.

  • This means that there is an excess of electrons on the zinc anode, and a deficit of electrons on the copper cathode.

  • Electrons will flow from an area of high concentration to an area of low concentration. Therefore the electrons on the zinc anode flow through the external circuit towards the more positive copper cathode.

  • The larger the difference between the excess and the deficit of electrons, the faster the electrons will flow and the greater the current will be.

  • The faster the electrons will flow, the greater the rate of the reaction must be.

  • Therefore the larger the current, the faster the rate of the reaction.

An electrolytic cell

  • Conversely, in an electrolytic cell a redox reaction takes place when a current is applied.

  • This redox reaction is the decomposition of a chemical compound (electrolysis).

  • The rate of this decomposition (into ions) is increased when the current applied is increased.

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