Question

How much heat is required to vaporize $ 80.6{\text{g}} $ of water at $ {100^0}C $ ? The heat of vaporization of water at $ {100^0}C $ is $ 40.7{\text{kJ/mol}}? $

Answer 1

Hint: This could be simply solved by applying the concepts of mole calculations. Also, we know that the heat being added to a substance during a phase change does not raise the temperature instead, it's being used to break the bonds in the solution. We shall just calculate the moles of water present.

Formula used: Here, we will use the number of moles formula:
 $ {\text{no of moles = }}\dfrac{{{\text{given mass}}}}{{{\text{molecular mass}}}} $

Complete step by step answer
We are given that $ 80.6{\text{g}} $ of water at $ {100^0}C $ .
At $ {100^0}C $ temperature change has already occurred. Now phase change will happen.
We are going to identify the moles of respective reactants.
Moles of water = $ \dfrac{{80.6}}{{18}} = 4.477 $
Now, multiply moles by the heat of vaporization, $ 40.7\;{\text{kJ/mole}}\; $ and you should get your answer.
 $ = 4.477{\text{mol}} \times 40.7{\text{kJ/mol}} = 182.213{\text{kJ}} $
Thus, the amount of heat applied to water to completely break the bonds between water molecules so it can completely vaporise= $ 182.213{\text{ kJ}} $ .
Dioxygen gas is the limiting reagent.
Thus, energy released can be based on the molar quantity of dioxygen gas = $ 1.3 \times {10^3}{\text{kJ}} $ .

Note
It should be always kept in mind that limiting reagent is defined as the reactant in a chemical reaction that limits the amount of product that can be formed. The reaction will stop when all of the limiting reactant is consumed. Excess Reactant - The reactant in a chemical reaction that remains when a reaction stops when the limiting reactant is completely consumed. In much the same way, a reactant in a chemical reaction can limit the amounts of products formed by the reaction. When this happens, we refer to the reactant as the limiting reactant (or limiting reagent).
And latent heat is defined as the heat or energy that is absorbed or released during a phase change of a substance. It could either be from a gas to a liquid or liquid to solid and vice versa. Latent heat is related to a heat property called enthalpy.