You are high up in the mountains and boil water to make some tea. However, when you drink your tea, it is not as hot as it should be. You try again and again, but the water is just not hot enough to make a hot cup of tea. Which is the best explanation for this result? (a) High in the mountains, it is probably very dry, and so the water is rapidly evaporating from your cup and cooling it. (b) High in the mountains, it is probably very windy, and so the water is rapidly evaporating from your cup and cooling it. (c) High in the mountains, the air pressure is significantly less than 1 atm, so the boiling point of water is much lower than at sea level. (d) High in the mountains, the air pressure is significantly less than 1 atm, so the boiling point of water is much higher than at sea level.

Key Concepts

Boiling Point and Atmospheric Pressure

The boiling point of a liquid is the temperature at which its vapor pressure equals the surrounding atmospheric pressure. At higher altitudes, such as in the mountains, the atmospheric pressure is lower than at sea level, which decreases the boiling point of water. This means that water will boil at a lower temperature, resulting in less heat available for making hot tea.

Vapor Pressure

Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid or solid form. As temperature increases, the vapor pressure of a liquid also increases, leading to boiling. In high-altitude conditions, the lower atmospheric pressure allows water to reach its boiling point at a lower temperature, which can affect the temperature of the water used for brewing tea.

Heat Transfer and Evaporation

Heat transfer occurs when thermal energy moves from a hotter object to a cooler one. Evaporation is a cooling process where molecules at the surface of a liquid gain enough energy to escape into the vapor phase. In high-altitude environments, rapid evaporation can occur, which may further cool the remaining liquid, making it difficult to achieve the desired temperature for hot tea.