Well, why is that? Well, this guy is simply the amount of free energy available to do useful work, while with this guy, the electrical work is the amount of energy transformed from chemical energy to electrical energy in the form of moving electrons. And this is also energy used to do useful work. So that's why the magnitude of these guys is the same, but the sign is different. So, why is it that we have a negative sign in front of the electrical work? Well, let's see why.