[一方「いっぽう」]だ => Change A continues, A does not stop N2
Miscellaneous
[代「か」]わり => Not A, but B, B in place of A, Instead of A, B; In exchange for A, B N3
Comparison, Exchange
[一方「いっぽう」] => On one hand A, on the other, B; Although A, at the same time, B N2
Contrast,Surprise