Sergey Bylikin, Gary Horner and, Brian Murphy Solutions for Chapter: Energetics and Thermochemistry (AHL), Exercise 5: Questions

The lattice enthalpy values for lithium fluoride and calcium fluoride are shown below.

$$\begin{gathered} \mathrm{LiF}\left(\mathrm{s}\right) △{\mathrm{H}}_{}^{⊝} = +1022 \mathrm{kJ} {\mathrm{mol}}^{-1} \\ {\mathrm{CaF}}_2\left(\mathrm{s}\right) △{\mathrm{H}}_{}^{⊝} = +2602 \mathrm{kJ} {\mathrm{mol}}^{-1} \end{gathered}$$

Which of the following statements help(s) to explain why the value for lithium fluoride is less than that for calcium fluoride?

I) The ionic radius of lithium is less than that of calcium.

II) The ionic charge of lithium is less than that of calcium.

Which reaction occurs with the largest increase in entropy?

The $\mathrm{\Delta H}$ and $\mathrm{\Delta S}$ values for a certain reaction are both positive. Which statement is correct about the spontaneity of this reaction at different temperatures?

The following reaction is spontaneous only at temperatures above $850°\mathrm{C}$.

${\mathrm{CaCO}}_3\left(\mathrm{s}\right) \to \mathrm{CaO}\left(\mathrm{s}\right) + {\mathrm{CO}}_2\left(\mathrm{g}\right)$

Which combination is correct for this reaction at $1000°\mathrm{C}$?

Explain in terms of $∆\mathrm{G}$, why a reaction for which both $∆\mathrm{H}$ and $∆\mathrm{S}$ values are positive can sometimes be spontaneous and sometimes not.

Define the term standard enthalpy change of formation and illustrate your answer with an equation, including state symbols, for the formation of nitric acid.

Propyne undergoes complete combustion as follows:

${\mathrm{C}}_3{\mathrm{H}}_4\left(\mathrm{g}\right) +4{\mathrm{O}}_2\left(\mathrm{g}\right) \to 3{\mathrm{CO}}_2\left(\mathrm{g}\right) + 2{\mathrm{H}}_2\mathrm{O} \left(\mathrm{l}\right)$

Calculate the enthalpy change of this reaction, given the following additional values:

$∆{\mathrm{H}}_{\mathrm{f}}^{⊝}$ of ${\mathrm{CO}}_2\left(\mathrm{g}\right)=-394 \mathrm{kJ} {\mathrm{mol}}^{-1}$
$∆{\mathrm{H}}_{\mathrm{f}}^{⊝}$ of ${\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) = -286 \mathrm{kJ} {\mathrm{mol}}^{-1}$
$∆{\mathrm{H}}_{\mathrm{f}}^{⊝}$ of ${\mathrm{C}}_3{\mathrm{H}}_4\left(\mathrm{g}\right) = 185.4 \mathrm{kJ} {\mathrm{mol}}^{-1}$

Propyne undergoes complete combustion as follows:

${\mathrm{C}}_3{\mathrm{H}}_4\left(\mathrm{g}\right) +4{\mathrm{O}}_2\left(\mathrm{g}\right) \to 3{\mathrm{CO}}_2\left(\mathrm{g}\right) + 2{\mathrm{H}}_2\mathrm{O} \left(\mathrm{l}\right)$

Predict and explain whether the value of $∆{\mathrm{S}}_{}^{⊝}$ for the reaction would be negative, close to zero, or positive.