16.4 Free energy  (Page 6/12)

What is the difference between Δ G , Δ G °, and $\text{Δ}{G}_{298}^{°}$ for a chemical change?

A reactions has $\text{Δ}{H}_{298}^{°}$ = 100 kJ/mol and $\text{Δ}{S}_{298}^{°}=\text{250 J/mol·K.}$ Is the reaction spontaneous at room temperature? If not, under what temperature conditions will it become spontaneous?

Explain what happens as a reaction starts with Δ G <0 (negative) and reaches the point where Δ G = 0.

Use the standard free energy of formation data in Appendix G to determine the free energy change for each of the following reactions, which are run under standard state conditions and 25 °C. Identify each as either spontaneous or nonspontaneous at these conditions.

(a) ${\text{MnO}}_2(s)⟶\text{Mn}(s)+{\text{O}}_2(g)$

(b) ${\text{H}}_2(g)+{\text{Br}}_2(l)⟶\text{2HBr}(g)$

(c) $\text{Cu}(s)+\text{S}(g)⟶\text{CuS}(s)$

(d) $\text{2LiOH}(s)+{\text{CO}}_2(g)⟶{\text{Li}}_2{\text{CO}}_3(s)+{\text{H}}_2\text{O}(g)$

(e) ${\text{CH}}_4(g)+{\text{O}}_2(g)⟶\text{C}(s,\text{graphite})+{\text{2H}}_2\text{O}(g)$

(f) ${\text{CS}}_2(g)+{\text{3Cl}}_2(g)⟶{\text{CCl}}_4(g)+{\text{S}}_2{\text{Cl}}_2(g)$

Use the standard free energy data in Appendix G to determine the free energy change for each of the following reactions, which are run under standard state conditions and 25 °C. Identify each as either spontaneous or nonspontaneous at these conditions.

(a) $\text{C}(s\text{, graphite})+{\text{O}}_2(g)⟶{\text{CO}}_2(g)$

(b) ${\text{O}}_2(g)+{\text{N}}_2(g)⟶\text{2NO}(g)$

(c) $\text{2Cu}(s)+\text{S}(g)⟶{\text{Cu}}_2\text{S}(s)$

(d) $\text{CaO}(s)+{\text{H}}_2\text{O}(l)⟶\text{Ca}{(\text{OH})}_2(s)$

(e) ${\text{Fe}}_2{\text{O}}_3(s)+\text{3CO}(g)⟶\text{2Fe}(s)+{\text{3CO}}_2(g)$

(f) ${\text{CaSO}}_4\text{·}{\text{2H}}_2\text{O}(s)⟶{\text{CaSO}}_4(s)+{\text{2H}}_2\text{O}(g)$

Given:
${\text{P}}_4(s)+{\text{5O}}_2(g)⟶{\text{P}}_4{\text{O}}_{10}(s)\text{Δ}{G}_{298}^{°}=\text{−2697.0 kJ/mol}$
${\text{2H}}_2(g)+{\text{O}}_2(g)⟶{\text{2H}}_2\text{O}(g)\text{Δ}{G}_{298}^{°}=\text{−457.18 kJ/mol}$
${\text{6H}}_2\text{O}(g)+{\text{P}}_4{\text{O}}_{10}(g)⟶{\text{4H}}_3{\text{PO}}_4(l)\text{Δ}{G}_{298}^{°}=\text{−428.66 kJ/mol}$

(a) Determine the standard free energy of formation, $\text{Δ}{G}_{\text{f}}^{°},$ for phosphoric acid.

(b) How does your calculated result compare to the value in Appendix G ? Explain.

Is the formation of ozone (O ₃ ( g )) from oxygen (O ₂ ( g )) spontaneous at room temperature under standard state conditions?

Consider the decomposition of red mercury(II) oxide under standard state conditions.
$\text{2HgO}(s,\text{red})⟶\text{2Hg}(l)+{\text{O}}_2(g)$

(a) Is the decomposition spontaneous under standard state conditions?

(b) Above what temperature does the reaction become spontaneous?