When we say that a reaction takes place at standard condition, we mean

Options

A. the temperature is the standard termodynamic tem-perature, `25^(@)C`, unless stated otherwise.
B. all reactants are at unit activity
C. all productes are at unit activity
D. All of these

Answer

D

Explanation

To compare potential of different galvanic cells, we must define a standard state for a galvanic cell. The standard state is defined in terms of the coencentration odf dissoloved substances and the pressure of gases, which together deter-mine tge cakye if the potential.
The standard state for cell potential is the same as the standard state for Gibbs energy. This mean that:
(i) Any solution species that takes part in the reaction is at a concentration of exactly `1 M` (the standard state is actually unit activity, which we are approximating as unit molarity),
(ii) Ang gas that takes part in the reactionis at a pressure of exactly `1` bar,
(iii) Any other substance that takes part in the reation is pure.
When we say ''takes part in the reaction" we mean either as a reactant or a pridcut when these conditions of con-centrationan and pressure (which are the same conditions that were described as standard conditions for thermodynamic purposes) are met, the cell displays what is called standard potential, whose symbol is `E_("cell")^(@)`. Since the `E_("cell")^(@)` of a galvanic cell is termperature dependent, we shall assume that all mea-surements are made at `298 K`, unless otherwide states. When one or more of these conditions is not satisfied, we must adjust our calculating for nonstandard conditions.