What is the difference between.acute & chronic renal failure?

Renal failure: Acute renal failure is a result of an injury, illness, or adverse drug reaction that injures your kidney (antibiotics, IV contrast, septic shock). Chronic renal failure is a progressive loss in renal function over a period of months or years and is the result of a disease process such as lupus, diabetes, polycystic kidney disease, etc.

The time duration: Chronic renal failure, or chronic kidney disease as it is now referred to, is kidney damage or reduction in kidney function that persists for 3 or more months. Anything less than that duration is "acute". These definitions apply regardless of the cause of kidney disease.