From these meanings (which actually apply in specific conditions, e.g. constant pressure, temperature, etc.), for positive changes (e.g., Δ U > 0), we can say that Δ U is the energy added to the system, Δ F is the total work done on it, Δ G is the non-mechanical work done on it, and Δ H is the sum of non-mechanical work done on the system and the heat given to it.