Final answer:
When a liquid is heated, bubbles appear due to reaching the boiling point where vapor pressure equals atmospheric pressure, causing the bubbles to rise and burst.
Explanation:
Bubbles appear when a liquid is heated because the liquid reaches its boiling point where the vapor pressure inside the bubble equals the external atmospheric pressure, causing the bubbles to rise to the surface and burst. As the temperature rises, the liquid molecules gain enough energy to break free from the forces holding them together, transitioning from a liquid to a gas state. Additionally, when a liquid is superheated, it can cause 'bumping' where bubbles erupt due to the temperature being above the boiling point without gas formation.
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