Sound waves generated in a classroom must through an open doorway in order to propagate into the hallway.

diffract through an open doorway in order to propagate into the hallway.

Diffract

Explanation:

The diffraction of sound waves is the description of how sound waves bend, change direction, as they travel around the edges of obstacles. The diffraction occurs as a result of the bending of sound waves as they find the path of least resistance to the travel path. The amount and magnitude of the diffraction occurs in proportion to the opening in the obstacle pathway. The diffraction is a property of sound that helps it bend around the corners and obstacles.

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.