Reps vs. Soreness.

Okay, it seems to me everytime i go into the gym and go for more reps i am much more sore the next few days then when i go in and lift for less reps. I.E.

chest workout one week:
14 x 8-10 about 65% max
More SORE This Week

chest workout next week:
14 x 5-7/8 80%
Less SORE but feel stronger next week?

Can anyone explain to me why this happens?

im not sure if lower reps make you more sore than high reps but im always more sore when doing high reps especially if ive been on a low rep 4-7 workout as opposed to high reps i think chest responds best with reps 5-8 for maximum growth peace