why does it take extra energy to turn a liquid to gas

Question

Why does it take extra energy to turn a liquid into a gas?

Answer 1

In the process of vaporization, for example in changing water to steam, you must add heat energy to the water in order to increase its temperature to the boiling point. The amount of heat energy added can be calculated by the equation: Q = mcΔT, where Q is the heat added, m is the mass of water, c is the specific heat constant of water and ΔT is the change in temperature of the water. Once all of the water reaches the boiling temperature, the heat energy added after this point does not cause the water to change temperature. Instead the heat energy is absorbed by the water molecules and it is used to change the molecules from the liquid phase to the gaseous phase. To calculate the heat of vaporization of water use the equation: H_vap = (n H_water), where H_vap is the heat energy of vaporization, n = the number of moles of water, H_water is the vaporization constant for water.

Once all of the liquid water is changed to gaseous water, then the temperature of the water in the gaseous state will increase if heat is being added.

Gaseous water contains more energy than liquid water due to the energy needed to change its state of matter because you first have to boil the water and then change it to steam. 

Steam burns are more severe than liquid water burns!

Answer 2

When a liquid turns into a gas, we call this process evaporation.  The liquid experiences an exposure to heat, which turns the liquid into a gas.  For example, water exposed to heat becomes steam.  Energy is what gives off heat.  So in order to have heat, you need to emit a lot of energy.