Describe how changing the air pressure affects the temperature at which water boils.

The boiling point of a liquid is the temperature at which it starts to change from a liquid to a gas. The boiling point of water is influenced by air pressure, which is the force that the air exerts on the liquid. At higher air pressures, it takes more energy (or higher temperatures) for the water molecules to escape the liquid and become a gas. Conversely, at lower air pressures, it takes less energy (or lower temperatures) for the water molecules to undergo the same phase transition.

The normal boiling point of water (100°C or 212°F) is the temperature at which water boils under standard atmospheric pressure (1 atmosphere or 101.3 kPa). When the air pressure deviates from this standard value, the boiling point of water changes accordingly.

When air pressure is higher than 1 atmosphere, such as in a pressure cooker, the boiling point of water increases. This is because the water molecules need more energy to overcome the stronger air pressure and change phase. For instance, inside a pressure cooker, the air pressure can reach up to 2 atmospheres, which raises the boiling point of water to approximately 121°C (250°F). This higher boiling point causes water to cook food quicker, as heat is transferred more efficiently.

Conversely, when air pressure is lower than 1 atmosphere, such as at high elevations like mountaintops, the boiling point of water decreases. The air pressure is lower due to there being less air pushing down on the liquid. For example, at an elevation of 3,048 meters (10,000 feet) above sea level, the air pressure is approximately 0.7 atmospheres, which lowers the boiling point of water to about 90°C (194°F). When cooking at high elevations, it takes longer to cook food because the water boils at a lower temperature and heat transfer is less efficient. In conclusion, the boiling point of water is highly dependent on air pressure. As air pressure increases, the boiling point of water goes up and vice versa. This relationship between air pressure and boiling point has significant implications for daily life, such as in cooking and refrigeration processes.