Final answer:
Vinegar and glass expand when heated, but vinegar expands more due to its higher coefficient of thermal expansion. A pocket of air above the vinegar in the jar can prevent the bottle from breaking by absorbing the expansion.
Step-by-step explanation:
When a glass bottle full of vinegar warms up, both the vinegar and the glass expand, but vinegar expands significantly more with temperature than glass. This is because substances expand when they are heated, and the degree of expansion depends on their coefficient of thermal expansion. Since vinegar has a higher coefficient of thermal expansion than glass, it expands more and can cause the bottle to break if it is tightly capped.
A pocket of air above the vinegar in the jar can prevent the break because air also expands when heated. This means that as the vinegar expands, the air in the pocket above it expands as well, relieving some of the pressure on the glass bottle. The air acts as a cushion, absorbing the expansion and preventing the bottle from breaking.