$2SO_2+O_2\rightarrow 2SO_3$
Ban đầu: $a a 0$Phản ứng: $x 0,5x $
Kết thúc: $(a-x) (a-0,5x) x$
$\Rightarrow h=\frac{100x}{2a}\% (x\leq a)$
$\frac{P'}{P}=\frac{2a-0,5x}{2a}\Rightarrow \frac{2a-0,5a}{2a}\leq \frac{P'}{P}\leq \frac{2a}{2a}\Rightarrow 0,75P\leq P'\leq P$