Eggshell is mainly composed of calcium carbonate. When calcium carbonate comes into contact with acetic acid, a chemical reaction will occur to produce carbon dioxide. The bubbles from eggshells soaked in vinegar are carbon dioxide bubbles produced by dissolution reaction. When calcium carbonate is dissolved in vinegar, the eggshell will become thinner and thinner, and even completely react.
As for the volume of the egg, it will increase to 1 times, which is caused by osmotic pressure. When the concentrations of substances (such as protein) on both sides of the membrane are not equal, osmotic pressure will be generated, and the water in the substances with lower concentration will permeate through the membrane to the other side, thus making the concentrations of substances on both sides of the membrane equal. The concentration of protein in eggs is relatively high. After the eggshell is thinned, under the action of osmotic pressure, the water in the vinegar penetrates through the translucent film formed after the eggshell is dissolved, and enters the egg to expand it.