Energy required for evaporation and energy released during condensation

Familiarize yourself with the concept of heat of vaporization. Compare the heat of vaporization of different amounts of water with the energy required to heat the liquids.

The amount of energy required to vaporize $1 k g$ of substance is called the heat of vaporization. Since the heat of vaporization depends on the temperature, the tables show the boiling heat of the substance, i.e., the heat of vaporization at the boiling temperature.

The amount of heat required for evaporation can be found using the formula

Q = L m

where $L$ is the heat of boiling and $m$ is the mass of the substance to be heated.

The amount of water to be tested and the initial and final temperature

Mass of water ( $k g$ )
Initial water temperature $^{\circ} C$
Final water temperature $^{\circ} C$

Calculator: Heat of Vaporization

The calculator calculates the amount of heat required for vaporization of substances or the amount of heat released during condensation. When using the calculator, enter the data in the table. The formula $Q = L m$ is used for calculation, where $L$ is the heat of vaporization of the substance and $m$ is the amount of water to be evaporated. The answer appears in the last row of the table.

Heat of vaporization of substance $L$	$\frac{k J}{k g}$
Mass $m$	$k g$
Evaporating/condensing the released amount of heat $Q = L m$	$J$

Boiling points and heats of vaporization of various substances at the boiling point (heat of boiling).

Calculator: amount of heat during heating and cooling of bodies

The calculator calculates the amount of heat required to heat bodies from a substance or the amount of heat released when they cool down, using the formula $Q = c m Δ t$ . When using the calculator, enter the data in the table. The answer appears in the last row of the table.

Specific heat $c$ of matter	$\frac{J}{^{\circ} C \cdot k g}$
Mass $m$	$k g$
Initial temperature $t_{1}^{\circ}$	$^{\circ} C$
Final temperature $t_{2}^{\circ}$	$^{\circ} C$
Temperature change $Δ t$	$^{\circ} C$
Internal energy change $Q = c m Δ t$	$J$ *

* A negative result indicates that the internal energy of the body decreased. A positive result indicates that the internal energy of the body increased.

The table shows the specific heats of several well-known substances.

The heat required to heat and evaporate the amount of water

Energy $J$ required to heat water
Energy $J$ required for water evaporation

Why do we calculate like this

The heat of vaporization is high, even higher than the heat of fusion. So it is also very large compared to the amount of heat we need to heat liquids. To arrive at this recognition, the preceding calculation is useful. We also need to understand that compared to the time it takes to boil water on the stove, it takes a very long time to boil the water.

What could be the reason that the formula for calculating the amount of heat contains the initial and final temperatures in addition to the mass, but the formula for calculating the heat of vaporization only contains the mass.

What do you think the energy given to the substance during evaporation is used for?

Heat of vaporization

Boiling points and heats of vaporization of some substances

Specific heats of some substances