What impact will splitting runs into 2 have?

The effort you’re spending thinking of these benign effects you could be training. Just run. When it hurts, don’t run. Run faster sometimes. Run slow when you’re tired.

You are unlikely to see much difference by breaking up mileage if you are reasonably well conditioned at those paces and distances. It’s no different from taking brief walk breaks if you feel like it; they won’t negate the training effect of the run portions. You might subconsciously run somewhat faster knowing that it’s only 3.5k compared to 7k, so that’s something that can alter your training intensity. If you weren’t doing long runs at all or were a beginner that rarely runs 7k or longer, there will be a difference between aerobic capacity training obtained by a 7k run compared to twice the number of 3.5K runs at the same pace.

*two haves

althoygh you could just say you are splitting your run in haf, to avoid repetition and redundancy