Chapter 10, Problem 143CP

Interpretation Introduction

Interpretation:

• The change in enthalpy of sublimation has to be calculated.

• The portion of intermolecular forces in ice that account for the formation of hydrogen bonding has to be estimated.

Concept Introduction:

Enthalpy is heat content of the system. The value of enthalpy does not depend on the path of a reaction but depend on state of the system. It has a unique value for each state of the system. Thus, enthalpy is a state function.

Enthalpy change, denoted by $\text{ΔH}$, refers to heat evolved or absorbed during a reaction. If heat is evolved in the reaction that is exothermic reaction $\text{ΔH}$ has negative value. For an endothermic reaction, $\text{ΔH}$ has positive value. $\text{ΔH}$ can be represented as,

                                              $\text{ΔH}\text{=}\text{ΔE}\text{+}\text{PΔV}$

                                    $\begin{array}{l}\text{where,}\text{ΔH}\text{=}\text{Change}\text{in}\text{enthalpy}\\ \text{ΔE}\text{=}\text{Change}\text{in}\text{Internal}\text{energy}\\ \text{ΔV}\text{=}\text{Change}\text{in}\text{volume}\\ \text{P}\text{=}\text{Pressure}\\ \\ \end{array}$

Enthalpy of sublimation is denoted by ${\text{ΔH}}_{\text{sub}}$. It is the enthalpy involved in sublimation process.

Internal energy of a system is total energy present in the system. In simple words, it is the sum of kinetic and potential energy of the particles in the system. According to First law of Thermodynamics, Energy of a system is conserved. It is only transferred from one state to another that is from system to surroundings and vice versa. So $\text{ΔE}$ can be represented as,

                                             ${\text{ΔE}}_{\text{universe}}\text{=}{\text{ΔE}}_{\text{sys}}\text{+}{\text{ΔE}}_{\text{surroundings}}$

Further, $\text{ΔE}$ is also equivalent to sum of either heat gained or lost and either work done on the system or by the system.

                                            $\text{ΔE}\text{=}\text{q}\text{+}\text{w}$

                                   $\begin{array}{l}\text{where}\text{ΔE}\text{=}\text{change}\text{in}\text{internal}\text{energy}\\ \text{q}\text{=}\text{quantity}\text{of}\text{heat}\text{gained}\text{or}\text{heat}\text{lost}\\ \text{w}\text{=}\text{work}\text{done}\end{array}$