In thermite reaction, a mixture of excess aluminum powder and iron(iii) oxide is ignited using magnesium ribbon. What chemical are found after the reaction is completed?

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?