A liquid begins to boil when
A liquid begins to boil when
- A) its volume is slightly decreased
- B) its vapour pressure is lower than the external pressure
- C) its vapour pressure equals the external pressure
- D) its molecules start escaping from the surface
Correct Answer: C) its vapour pressure equals the external pressure
Explanation
A liquid begins to boil when its vapour pressure equals the external pressure.Boiling is the process by which a liquid turns into a gas as it is heated. This occurs when the temperature of the liquid is high enough for its molecules to have enough energy to overcome the attractive forces holding them together. In simpler terms, the molecules in the liquid move more rapidly, and some of them gain enough energy to escape as gas.
The vapour pressure of a liquid is the pressure exerted by its vapour when it is in equilibrium with the liquid. As the temperature of a liquid increases, its vapour pressure also increases. When the vapour pressure of the liquid becomes equal to the external pressure (usually atmospheric pressure), the liquid starts to boil.
This means that boiling points can vary depending on the external pressure. For example, at high altitudes, where the atmospheric pressure is lower, liquids boil at lower temperatures than they do at sea level.