When a strip of zinc metal is added to a test tube of hydrochloric acid, the liquid forms bubbles, and the test tube feels hot. The bubbles are a result of the formation of hydrogen gas. What does the hot test tube indicate?

Exothermic Reaction

Explanation:

The test tube feels hot as a result of an increase in temperature of the surroundings. This means that due to the reaction between zinc metal and hydrochloric acid, heat was released. The hot test tube indicates that this is an exothermic reaction.

answer : one can design an experiment using a liquid and an additive that can be added to the liquid and observe the chemical changes in the reaction species.

one would need a beaker which is filled with a known amount of the liquid in which thermometer is placed to measure the temperature changes; after addition of the additive to the liquid solution one can note down the temperature change and find whether the reaction is endothermic or exothermic in nature. by subtracting the initial temperature value with the final temperature one can find the temperature changes.

various combinations of liquid and additive can be used. liquid in this case can be a known quantity of water and additives can be epsom salt or without epsom salt the experiment can be conducted to notice the changes. water and ice, hydrogen peroxide and dry yeast, vinegar and baking soda,etc.