91Ó°ÊÓ

Calculate${\mathbf{\text{Δ³Ò}}}^{\mathbf{\text{°}}}$ for each reaction using${\mathbf{\text{Δ³Ò}}}_{\mathbf{\text{f}}}^{\mathbf{\text{°}}}$ values:

(a)${\mathbf{\text{H}}}_{\mathbf{\text{2}}}{\mathbf{\text{(g)+I}}}_{\mathbf{\text{2}}}\mathbf{\text{(s)}}\mathbf{→}\mathbf{\text{2HI(g)}}$

(b)${\mathbf{\text{MnO}}}_{\mathbf{\text{2}}}\mathbf{\text{(s)+2CO(g)}}\mathbf{→}{\mathbf{\text{Mn(s)+2CO}}}_{\mathbf{\text{2}}}\mathbf{\text{(g)}}$

(c)${\mathbf{\text{NH}}}_{\mathbf{\text{4}}}\mathbf{\text{Cl(s)}}\mathbf{→}{\mathbf{\text{NH}}}_{\mathbf{\text{3}}}\mathbf{\text{(g)+HCl(g)}}$

Find ${\mathbf{Δ³Ò}}^{\mathbf{∘}}$ for the reactions in Problem 20.50 using ${\mathbf{Δ\pm á}}_{\mathbf{f}}^{\mathbf{∘}}$ and ${\mathbf{S}}^{\mathbf{∘}}$ values.

Find ${\mathbf{\text{Δ³Ò}}}^{\mathbf{\text{°}}}$for the reactions in Problem 20.51 using ${\mathbf{\text{Δ±á}}}_{\mathbf{\text{f}}}^{\mathbf{\text{°}}}$andSvalues.

Consider the oxidation of carbon monoxide:

$\mathbf{\text{CO(g)+}}\frac{\mathbf{\text{1}}}{\mathbf{\text{2}}}{\mathbf{\text{O}}}_{\mathbf{\text{2}}}\mathbf{\text{(g)}}\mathbf{→}{\mathbf{\text{CO}}}_{\mathbf{\text{2}}}\mathbf{\text{(g)}}$

(a) Predict the signs of${\mathbf{\text{Δ³§}}}^{\mathbf{\text{°}}}$ and${\mathbf{\text{Δ±á}}}^{\mathbf{\text{°}}}$ . Explain.

(b) Calculate${\text{Δ³Ò}}^{\text{°}}$ by two different methods

Consider the combustion of butane gas:

${\mathbf{\text{C}}}_{\mathbf{\text{4}}}{\mathbf{\text{H}}}_{\mathbf{\text{10}}}\mathbf{\text{(g)+}}\frac{\mathbf{\text{13}}}{\mathbf{\text{2}}}{\mathbf{\text{O}}}_{\mathbf{\text{2}}}\mathbf{\text{(g)}}\mathbf{→}{\mathbf{\text{4CO}}}_{\mathbf{\text{2}}}{\mathbf{\text{(g)+5H}}}_{\mathbf{\text{2}}}\mathbf{\text{O(g)}}$

(a) Predict the signs of ${\mathbf{\text{Δ³§}}}^{\mathbf{\text{°}}}{\mathbf{\text{andΔ±á}}}^{\mathbf{\text{°}}}$. Explain.

(b) Calculate${\mathbf{\text{Δ³Ò}}}^{\mathbf{\text{°}}}$ by two different methods.

For the gaseous reaction of xenon and fluorine to form xenon hexafluoride:

(a) Calculate${\mathbf{\text{Δ³§}}}^{\mathbf{\text{°}}}$ at $\mathbf{\text{298K}}\mathbf{(}{\mathbf{\text{Δ±á}}}^{\mathbf{\text{°}}}\mathbf{\text{=-402kJ/mol}}$and ${\mathbf{\text{Δ³Ò}}}^{\mathbf{\text{°}}}\mathbf{\text{=-280.kJ/mol}}$).

(b) Assuming that${\mathbf{\text{Δ³§}}}^{\mathbf{\text{°}}}$ and ${\mathbf{\text{Δ±á}}}^{\mathbf{\text{°}}}$change little with temperature, calculate ${\mathbf{\text{Δ³Ò}}}^{\mathbf{\text{°}}}$at 500. K.

For the gaseous reaction of carbon monoxide and chlorine to form phosgene $\mathbf{\left(}{\mathbf{\text{COCl}}}_{\mathbf{\text{2}}}\mathbf{\right)}$:

(a) Calculate${\mathbf{\text{Δ³§}}}^{\mathbf{\text{°}}}$ at $\mathbf{\text{298K}}\mathbf{(}{\mathbf{\text{Δ±á}}}^{\mathbf{\text{°}}}\mathbf{\text{=-220.kJ/mol}}$and ${\mathbf{\text{Δ³Ò}}}^{\mathbf{\text{°}}}\mathbf{\text{=-206kJ/mol)}}$.

(b) Assuming that${\mathbf{\text{Δ³§}}}^{\mathbf{\text{°}}}$ and${\mathbf{\text{Δ±á}}}^{\mathbf{\text{°}}}$ change little with temperature, calculate${\mathbf{\text{Δ³Ò}}}^{\mathbf{\text{°}}}$ at $\text{450.K}$.

One reaction used to produce small quantities of pure${\mathbf{\text{H}}}_{\mathbf{\text{2}}}$ is

${\mathbf{\text{CH}}}_{\mathbf{\text{3}}}\mathbf{\text{OH(g)}}\mathbf{⇌}{\mathbf{\text{CO(g)+2H}}}_{\mathbf{\text{2}}}\mathbf{\text{(g)}}$

(a) Determine${\mathbf{\text{Δ±á}}}^{\mathbf{\text{°}}}$ and${\mathbf{\text{Δ³§}}}^{\mathbf{\text{°}}}$ for the reaction at$\mathbf{\text{298K}}$ .

(b) Assuming that these values are relatively independent of temperature, calculate ${\mathbf{\text{Δ³Ò}}}^{\mathbf{\text{°}}}$at${\mathbf{\text{28}}}^{\mathbf{\text{°}}}{\mathbf{\text{C,128}}}^{\mathbf{\text{°}}}\mathbf{\text{C}}$ , and${\mathbf{\text{228}}}^{\mathbf{\text{°}}}\mathbf{\text{C}}$.

(c) What is the significance of the different values of ${\mathbf{\text{Δ³Ò}}}^{\mathbf{\text{°}}}$?

A reaction that occurs in the internal combustion engine is

${\mathbf{\text{N}}}_{\mathbf{\text{2}}}{\mathbf{\text{(g)+O}}}_{\mathbf{\text{2}}}\mathbf{\text{(g)}}\mathbf{⇌}\mathbf{\text{2NO(g)}}$

(a) Determine${\mathbf{\text{Δ±á}}}^{\mathbf{\text{°}}}$ and${\mathbf{\text{Δ³§}}}^{\mathbf{\text{°}}}$ for the reaction at $\mathbf{\text{298K}}$.

(b) Assuming that these values are relatively independent of temperature, calculate ${\mathbf{\text{Δ³Ò}}}^{\mathbf{\text{°}}}$at ${\mathbf{\text{100.}}}^{\mathbf{\text{°}}}{\mathbf{\text{C,2560.}}}^{\mathbf{\text{°}}}\mathbf{\text{C}}$, and ${\mathbf{\text{3540.}}}^{\mathbf{\text{°}}}\mathbf{\text{C}}$.

(c) What is the significance of the different values of${\mathbf{\text{Δ³Ò}}}^{\mathbf{\text{°}}}$ ?

Why is$∆{\text{S}}_{\text{vap}}$of a substance always larger than $∆{\text{S}}_{\text{fus}}$.