If an 18 wheeler and a sports car collide head on which vehicle will experience the greater force of impacr? The greater impulse? The greater change in momentum? The greater acceleration?

You mean the greater deceleration. I would assume they would experience the same force of impact, if they were traveling at the same speed. However the sports car only weighs what, 1/2 ton if that, while the 18 wheeler is multiple tons, so you have to assume the 18 wheeler won't come to a dead stop, the sports car will, the 18 wheeler with continue to coast to a stop. The drivers would feel different forces acting on them, because going from 60 to 0 in a second is a lot worst then going from 60 to 0 in a matter of 15 seconds.