Given the balanced equation representing a reaction: 2h2 o2 = 2h2o, what is the total mass of water formed when 8 grams of hydrogen reacts completely with 64 grams of oxygen?

When the chemicals iron sulfide (fes) and hydrochloric acid (hcl) are combined, bubbles appear from the mixture. 1. does the appearance of bubbles indicate a physical or chemical change? 2. why do the bubbles indicate this change? 3. what property is this?