▁a ▁fan ▁is ▁used ▁to ▁maintain ▁the ▁flow ▁of ▁gas ▁through ▁the ▁scr ub bing ▁can ister . ▁ ▁Chem ical ▁reaction ▁ ▁The ▁overall ▁reaction ▁is : ▁ ▁CO 2 ▁+ ▁Ca ( OH ) 2 ▁→ ▁Ca CO 3 ▁+ ▁H 2 O ▁+ ▁heat ▁( in ▁the ▁presence ▁of ▁water ) ▁ ▁Each ▁mole ▁of ▁CO 2 ▁( 4 4 ▁g ) ▁react ing ▁with ▁calci um ▁hydro x ide ▁produces ▁one ▁mole ▁of ▁water ▁( 1 8 ▁g ). ▁ ▁The ▁reaction ▁can ▁be ▁considered ▁as ▁a ▁strong - base - catal ys ed , ▁water - fac il itated ▁reaction . ▁ ▁The ▁reaction ▁mechanism ▁of ▁carbon ▁dio x ide ▁with ▁s oda ▁l ime ▁can ▁be ▁decom posed ▁in ▁three ▁elementary ▁steps : ▁▁ 1 ) ▁CO 2 ( g ) ▁→ ▁CO 2 ( a q ) ▁▁▁▁▁▁▁▁▁▁▁▁ ▁( CO 2 ▁dissol ves ▁in ▁water ▁– ▁slow ▁and ▁rate - det erm ining ) ▁▁ 2 ) ▁CO 2 ( a q ) ▁+ ▁Na OH ▁→ ▁Na H CO 3 ▁▁▁▁▁▁▁▁▁▁▁▁ ▁( b ic ar bon ate ▁formation ▁at ▁high ▁p H ) ▁▁ 3 ) ▁Na H CO 3 ▁+ ▁Ca ( OH ) 2 ▁→ ▁Ca CO 3 ▁+ ▁H 2 O ▁+ ▁Na OH ▁ ▁( Na OH ▁rec yc led ▁to ▁step ▁ 2 ▁– ▁hence ▁a ▁catal yst ) ▁ ▁This ▁sequence ▁of ▁re actions ▁explains ▁the ▁catal yt ic ▁role ▁played ▁by ▁sod ium ▁hydro x ide ▁in ▁the