Graham-W and factor30 are correct, but I don't know if zinc nitride can be made readily in this way. Lithium metal reacts with nitrogen gas at room temperature and pressure, to give lithium nitride, so in principle I suppose it is possible.
A brief survey suggests to me that it's usually made by heating zinc in ammonia gas, the other product then being hydrogen. There's a short Wikipedia article http://en.wikipedia.org/wiki/Zinc_nitride
Can't see that it makes any difference how the reaction takes place. The equation simply represents a summary of the results.
The states of the various materials is often (normally?) omitted. I think it is put in here just because he mentioned it specifically. I wonder if you specify these states whether you also need to include energy as part of the equation?
Well, Merlin3189, the reaction used generally to make the material is different from the reaction that MJFan101 asked about - the reaction equation would be different. Some people may be interested in this. And how reactions take place is of key importance in understanding and controlling them. The delta G/delta H/delta S values are probably out there, but I didn't look that up as MJFan101 didn't ask about the energetics. The equation is correct without mention of the energy changes involved.