Work done by a system is positive or negative?

The internal energy has the symbol U. Q is positive if heat is added to the system, and negative if heat is removed;

"W is positive if work is done by the system"

and negative if work is done on the system.

So, work done by a system is positive.

Hno3(aq) → h+(aq) + no3−(aq). picture ii best represents the strong acid hno3. strong acids are strong electrolytes