▁system ▁and ▁why ▁s oda ▁l ime ▁is ▁faster ▁in ▁chemical ▁react ivity ▁than ▁calci um ▁hydro x ide ▁alone . ▁The ▁mo ist ▁Na OH ▁im pre gn ates ▁the ▁surface ▁and ▁the ▁por os ity ▁of ▁calci um ▁hydro x ide ▁gra ins ▁with ▁a ▁high ▁specific ▁surface ▁area . ▁It ▁react s ▁much ▁more ▁quickly ▁and ▁so ▁cont ributes ▁to ▁a ▁faster ▁elim ination ▁of ▁the ▁CO 2 ▁from ▁the ▁re bre ath ing ▁circuit . ▁The ▁formation ▁of ▁water ▁by ▁the ▁reaction ▁and ▁the ▁mo ist ure ▁from ▁the ▁resp iration ▁also ▁act ▁as ▁a ▁sol vent ▁for ▁the ▁reaction . ▁Re actions ▁in ▁a que ous ▁phase ▁are ▁generally ▁faster ▁than ▁between ▁a ▁dry ▁gas ▁and ▁a ▁dry ▁solid . ▁S oda ▁l ime ▁is ▁commonly ▁used ▁in ▁closed - circ uit ▁div ing ▁re bre athers ▁and ▁in ▁an est hes ia ▁systems . ▁ ▁The ▁same ▁catal yt ic ▁effect ▁by ▁the ▁alk ali ▁hydro x ides ▁( function ▁of ▁the ▁Na 2 O eq ▁content ▁of ▁c ement ) ▁also ▁cont ributes ▁to ▁the ▁carbon ation ▁of ▁port land ite ▁by ▁atmos pher ic ▁CO 2 ▁in ▁concrete ▁although ▁the ▁rate ▁of ▁propag ation ▁of ▁the ▁reaction ▁front ▁is ▁there ▁essentially ▁limited ▁by ▁the ▁CO 2 ▁diffusion ▁within ▁the ▁concrete ▁matrix ▁less ▁por ous . ▁ ▁Anal ogy ▁with ▁the ▁alk ali - sil ica ▁reaction ▁ ▁A ▁similar ▁reaction ▁to ▁above , ▁also ▁catal ys ed ▁by ▁sod ium ▁hydro x ide , ▁is