What is the mass of the missing reactant in the following reactions, given that the reaction goes to completion? do not include units. - 2.7 g water + g carbon dioxide --> 9.3 g carbonic acid - 32.0 g sodium hydroxide + 16.0 g hydrofluoric acid --> g water + 33.6 g sodium fluoride - 0.60 g calcium carbonate + 0.48 g sodium hydroxide --> g sodium carbonate + 0.45 g calcium hydroxide - 0.53 g sodium hydroxide + 0.37 g carbon dioxide --> g sodium hydrogen carbonate

1)  2.7 g water + 6,6 g carbon dioxide → 9.3 g carbonic acid.
According to principle of mass conservation mass of reactants and products are the same after chemical reactio. 2,7 g + 6,6 g = 9,3 g.
2) 32.0 g sodium hydroxide + 16.0 g hydrofluoric acid --> 14,4 g water + 33.6 g sodium fluoride.
m(water) = 32 g + 16 g - 33,6 g.
3) 0.60 g calcium carbonate + 0.48 g sodium hydroxide --> 0,63 g sodium carbonate + 0.45 g calcium.
m(sodium carbonate) = 0,6 g + 0,48 g - 0,45 g.
4) 0.53 g sodium hydroxide + 0.37 g carbon dioxide --> 0,9 g sodium hydrogen carbonate.
m(sodium hydrogen carbonate) = 0,53 g + 0,37 g = 0,9 g.

Yes, endothermic means it turns cold. and some chemical changes include change of tempature.