the difference between intercession and mediation

I could use some wisdom and theological expertise.

The terms intercession and mediation are very similar. In Christ's relation to as as our High Priest he is both and both require that he be between us and God. In Romans 8:34 he is our intercessor and in 1Timothy 2:5 he is our mediator in both he represents man to God. Here is my question, what is the difference in how he represents man?

The best I have been able to come with is that interecession is the process of Christ extending grace to us whereby he extends himself to God on our behalf through his attributes of goodnes, kindness and benevolence etc. in another word he intercedes of his own free will.
As a mediator he represents us to God from the attribute of justice having paid the penalty and thereby declaring us innocent to God the penalty having been paid.

What are your thoughts?

thjplgvp