Suggest a reason for only ‘roughly’ twice as much hydrogen gas being produced at the cathode as oxygen gas at the anode in the electrolysis of water.

Spontaneity tell us the direction of the reaction, but not how fast it goes. gibbs free energy brings together enthalpy, entropy and temperature in one easy formula. g = h - ts. and, finally the sign of delta g is always negative for a spontaneous reaction.

It is 4.92 e-4 sorry if i am wrong