Water Evaporates at 100 Degrees Celsius Calculate Delta E

When water evaporates at 100°C, it absorbs energy to transition from liquid to vapor. This energy change (ΔE) is crucial in thermodynamics, meteorology, and industrial processes. This guide explains how to calculate ΔE for water evaporation at 100°C using the latent heat of vaporization.

What is ΔE in water evaporation?

ΔE (delta E) represents the energy change associated with a phase transition. For water evaporating at 100°C, ΔE is the energy required to convert liquid water into water vapor at the boiling point.

This energy is absorbed from the surroundings, causing the temperature to remain constant during the phase change (at 100°C under standard conditions). The latent heat of vaporization (L) is a key property in this calculation.

The formula for ΔE

Energy required for evaporation

ΔE = m × L

Where:

ΔE = energy required (Joules, J)
m = mass of water (kilograms, kg)
L = latent heat of vaporization for water at 100°C (2,260,000 J/kg)

The latent heat of vaporization (L) is the energy required to vaporize 1 kg of water at 100°C. This value is constant at standard pressure (1 atm).

How to calculate ΔE

Determine the mass of water (m) in kilograms.
Use the latent heat of vaporization (L) for water at 100°C (2,260,000 J/kg).
Multiply the mass by the latent heat to get ΔE.

For example, if you have 0.5 kg of water, the energy required for evaporation would be:

Example calculation

ΔE = 0.5 kg × 2,260,000 J/kg = 1,130,000 J

Worked example

Let's calculate ΔE for 1 kg of water evaporating at 100°C:

Mass (m) = 1 kg
Latent heat (L) = 2,260,000 J/kg
ΔE = 1 × 2,260,000 = 2,260,000 J

This means 2,260,000 Joules of energy are required to evaporate 1 kg of water at 100°C.

Energy units

1 Joule (J) is the standard unit of energy in the International System of Units (SI). For larger quantities, you might convert to kilojoules (kJ) where 1 kJ = 1,000 J.

FAQ

Why does water evaporate at 100°C?: Water boils at 100°C under standard atmospheric pressure (1 atm) because this is the temperature at which the vapor pressure of water equals the external pressure.
What happens to the temperature during evaporation?: The temperature remains constant at 100°C during evaporation because all added energy goes into changing the phase, not increasing the temperature.
Can ΔE be negative?: No, ΔE is always positive for evaporation because energy is absorbed from the surroundings to break intermolecular bonds during vaporization.
Does altitude affect the latent heat of vaporization?: Yes, at higher altitudes where atmospheric pressure is lower, water boils at lower temperatures, and the latent heat of vaporization decreases slightly.
How is ΔE used in real-world applications?: ΔE calculations are used in meteorology to study cloud formation, in industrial processes like distillation, and in energy efficiency assessments for HVAC systems.