I need help pls

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?

The density of the solid phase of a substance is 0.90 g/cm3 and the density of the liquid phase is 1.0 g/cm3. a large increase in pressure will a. lower the freezing point b. raise the freezing point c. lower the boiling point d. raise the triple point e. lower the triple point

Ahelium balloon contains 16.9 l of helium at stp. how many atoms of helium are in the balloon