Difference between W/Q and E/Q in Electricity

In the Electricity section of the AQA A Level Physics data sheet (link given bellow) it includes these 3 equations:
http://store.aqa.org.uk/qual/gce/pdf...5-W-A2-DFB.PDF

V=W/Q
Emf = E/Q
Emf = I(R+r)

I understand that Emf and Voltage both have the unit Volts, and Work Done and Energy both have the unit Joules, so V=W/Q and Emf = E/Q are basically the same equation.

And I also understand that it is convention to call the voltage across a battery V, and the voltage it would theoretically have across it if it had no internal resistance emf. That is why Emf = I(R+r). IR would be the voltage across the battery, (or whole circuit) and Ir would be the voltage across the internal resistance of the battery.

But why is V=W/Q and Emf = E/Q?

Thanks