What is the biggest different between reversible and irrevis

What is the biggest different between reversible and irrevisible reaction on its entropy? I am quite new to the subject.

Solution

We can not measure the exact entropy at a point. We can only calculate the change in entropy between two points.

For a reversible reaction, the initial and final points are same. Hence the change in entropy is zero.

where as for an irreversible reaction , the change in entropy always increases and is positive.