Final answer:
The capacity of air to hold water vapor decreases with temperature; therefore, air can hold more water vapor at 25°C than at 5°C. With a decrease in temperature from 25°C to 5°C, excess water vapor may condense, leading to the formation of dew or fog.
Step-by-step explanation:
The difference in the amount of water vapor that can be held in a kilogram of air at 25°C compared to 5°C is due to the change in air's capacity to hold moisture with temperature, which is explained by the concept of saturation vapor density. Warm air can hold more water vapor before it becomes saturated, hence at 25°C it can hold a significantly greater amount compared to 5°C. When the temperature drops, the air's capacity to hold water vapor reduces, leading to condensation and possible formation of dew or fog, as the water vapor content exceeds the saturation vapor density for the cooler temperature.
The quantitative details of how much water vapor air can hold at different temperatures can be found in tables or determined using formulas from thermodynamics which relate temperature, vapor pressure, and relative humidity. An understanding of the principles of relative humidity and dew point is pivotal in calculations involving atmospheric moisture and temperature changes.