Because if you plot the second derivative, (that is, (Δ(ΔpH/ΔV)/ΔV) versus Volume), you'll see that the equivalence point corresponds to the volume where the graph crosses the x-axis (or at (Δ(ΔpH/ΔV)/ΔV) = 0).
From there you can easily read the volume at equivalence point, unlike in the first derivative (ΔpH/ΔV versus Volume), where the volume at equivalence point is the top of the "spike" in the graph or when ΔpH/ΔV is at the maximum/highest point.
hope this helps~ `u`
Why is the second derivative of a titration curve more accurate method to determine endpoints and equivalence points than the first derivative?
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