Which one of the following statements is not correct? A Since voltage depends on concentrations, using standard conditions makes it easier to compare different electrochemical reactions. B We have to measure the cell potential to obtain the difference in potential energy because the potential of half-reactions cannot be measured directly. C The direction of a redox reaction can only be determined experimentally. D Half-cell potentials for half-reactions are determined by combining the relevant half-cell with a standardised half-cell.