Do H2O Temperatures Affect the Boiling Time of Water?

Water boils when its vapor pressure equals atmospheric pressure.

Kinetic energy is the energy of motion. Temperature measures the average kinetic energy of molecules in a substance. Increasing the temperature of water in a pot means increasing the kinetic energy of the water molecules. This process requires energy in the form of heat.

Heat Capacity

The heat capacity of water (i.e., the amount of thermal energy it takes to increase the temperature of water by 1 degree) is 4.184 joules per grams degrees Kelvin. This means that it takes 4.184 joules of heat energy to boost the temperature of the water in the pot by 1 degree. Your stovetop can only supply heat at a limited rate, so the colder the water is, the longer it will take to bring the water to boiling temperature.

Considerations

All else being equal, the colder the water is, the longer it will take to come to a boil. The rate at which the water absorbs heat, however, will decrease as it heats up, since the rate of heat flow through conduction decreases as the temperature of the water approaches the temperature of the stove. Regardless, since the cold water starts out at a lower temperature, it will take longer to boil.

Altitude

When the pressure exerted by the surrounding atmosphere increases, it takes more energy for water molecules to escape the water and form a vapor. Consequently, the temperature at which water boils depends on pressure. At higher altitudes the atmospheric pressure is lower, so the boiling point of water is lower. Assuming you supply heat at the same rate, it will take less time for hot or cold water to boil at higher altitude.

References

• "Physics for Scientists and Engineers"; Richard Wolfson and Jay Pasachoff; 1999
• University of Waterloo: The Clasius-Clapeyron Equation
• University of Illinois Department of Physics: Ask the Van: Boiling Times