5.3 Enthalpy  (Page 12/25)

Calculate $\text{Δ}{H}_{298}^{°}$ for the process $\text{Zn}\left(s\right)+\text{S}\left(s\right)+2{\text{O}}_2(g)⟶{\text{ZnSO}}_4(s)$

from the following information:
$\begin{array}{l}\text{Zn}(s)+\text{S}(s)⟶\text{ZnS}(s)\text{Δ}{H}_{298}^{°}=\mathrm{-206.0}\text{kJ}\\ \text{ZnS}(s)+{\text{2O}}_2(g)⟶{\text{ZnSO}}_4(s)\text{Δ}{H}_{298}^{°}=\mathrm{-776.8}\text{kJ}\end{array}$

Calculate Δ H for the process ${\text{Hg}}_2{\text{Cl}}_2(s)⟶2\text{Hg}\left(l\right)+{\text{Cl}}_2(g)$

from the following information:
$\begin{array}{l}\text{Hg}(l)+{\text{Cl}}_2(g)⟶{\text{HgCl}}_2(s)\text{Δ}H=\mathrm{-224}\text{kJ}\\ \text{Hg}(l)+{\text{HgCl}}_2(s)⟶{\text{Hg}}_2{\text{Cl}}_2(s)\text{Δ}H=\mathrm{-41.2}\text{kJ}\end{array}$

Calculate $\text{Δ}{H}_{298}^{°}$ for the process ${\text{Co}}_3{\text{O}}_4(s)⟶3\text{Co}\left(s\right)+2{\text{O}}_2(g)$

from the following information:
$\begin{array}{}\\ \text{Co}(s)+\frac{1}{2}{\text{O}}_2(g)⟶\text{CoO}(s)\text{Δ}{H}_{298}^{°}=\mathrm{-237.9}\text{kJ}\\ \text{3Co}(s)+\frac{1}{2}{\text{O}}_2(g)⟶{\text{Co}}_3{\text{O}}_4(s)\text{Δ}{H}_{298}^{°}=\mathrm{-177.5}\text{kJ}\end{array}$

Calculate the standard molar enthalpy of formation of NO( g ) from the following data:
$\begin{array}{l}{\text{N}}_2(g)+2{\text{O}}_2⟶2{\text{NO}}_2(g)\text{Δ}{H}_{298}^{°}=66.4\text{kJ}\\ \text{2NO}(g)+{\text{O}}_2⟶2{\text{NO}}_2(g)\text{Δ}{H}_{298}^{°}=\mathrm{-114.1}\text{kJ}\end{array}$

Using the data in Appendix G , calculate the standard enthalpy change for each of the following reactions:

(a) ${\text{N}}_2(g)+{\text{O}}_2(g)⟶2\text{NO}\left(g\right)$

(b) $\text{Si}\left(s\right)+2{\text{Cl}}_2(g)⟶{\text{SiCl}}_4(g)$

(c) ${\text{Fe}}_2{\text{O}}_3\left(s\right)+3{\text{H}}_2(g)⟶2\text{Fe}\left(s\right)+3{\text{H}}_2\text{O}\left(l\right)$

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

Using the data in Appendix G , calculate the standard enthalpy change for each of the following reactions:

(a) $\text{Si}\left(s\right)+2{\text{F}}_2(g)⟶{\text{SiF}}_4(g)$

(b) $2\text{C}\left(s\right)+2{\text{H}}_2(g)+{\text{O}}_2(g)⟶{\text{CH}}_3{\text{CO}}_2\text{H}\left(l\right)$

(c) ${\text{CH}}_4(g)+{\text{N}}_2(g)⟶\text{HCN}\left(g\right)+{\text{NH}}_3(g)\text{;}$

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

The following reactions can be used to prepare samples of metals. Determine the enthalpy change under standard state conditions for each.

(a) $2{\text{Ag}}_2\text{O}\left(s\right)⟶4\text{Ag}\left(s\right)+{\text{O}}_2(g)$

(b) $\text{SnO}\left(s\right)+\text{CO}\left(g\right)⟶\text{Sn}\left(s\right)+{\text{CO}}_2(g)$

(c) ${\text{Cr}}_2{\text{O}}_3(s)+3{\text{H}}_2(g)⟶2\text{Cr}\left(s\right)+3{\text{H}}_2\text{O}\left(l\right)$

(d) $2\text{Al}\left(s\right)+{\text{Fe}}_2{\text{O}}_3(s)⟶{\text{Al}}_2{\text{O}}_3(s)+2\text{Fe}\left(s\right)$

The decomposition of hydrogen peroxide, H ₂ O ₂ , has been used to provide thrust in the control jets of various space vehicles. Using the data in Appendix G , determine how much heat is produced by the decomposition of exactly 1 mole of H ₂ O ₂ under standard conditions.
$2{\text{H}}_2{\text{O}}_2(l)⟶2{\text{H}}_2\text{O}\left(g\right)+{\text{O}}_2(g)$

Calculate the enthalpy of combustion of propane, C ₃ H ₈ ( g ), for the formation of H ₂ O( g ) and CO ₂ ( g ). The enthalpy of formation of propane is −104 kJ/mol.

Calculate the enthalpy of combustion of butane, C ₄ H ₁₀ ( g ) for the formation of H ₂ O( g ) and CO ₂ ( g ). The enthalpy of formation of butane is −126 kJ/mol.

Both propane and butane are used as gaseous fuels. Which compound produces more heat per gram when burned?

The white pigment TiO ₂ is prepared by the reaction of titanium tetrachloride, TiCl ₄ , with water vapor in the gas phase: ${\text{TiCl}}_4(g)+2{\text{H}}_2\text{O}\left(g\right)⟶{\text{TiO}}_2(s)+4\text{HCl}\left(g\right).$

How much heat is evolved in the production of exactly 1 mole of TiO ₂ ( s ) under standard state conditions?

Water gas, a mixture of H ₂ and CO, is an important industrial fuel produced by the reaction of steam with red hot coke, essentially pure carbon: $\text{C}\left(s\right)+{\text{H}}_2\text{O}\left(g\right)⟶\text{CO}\left(g\right)+{\text{H}}_2(g).$

(a) Assuming that coke has the same enthalpy of formation as graphite, calculate $\text{Δ}{H}_{298}^{°}$ for this reaction.

(b) Methanol, a liquid fuel that could possibly replace gasoline, can be prepared from water gas and additional hydrogen at high temperature and pressure in the presence of a suitable catalyst: $2{\text{H}}_2(g)+\text{CO}(g)⟶{\text{CH}}_3\text{OH}(g).$

Under the conditions of the reaction, methanol forms as a gas. Calculate $\text{Δ}{H}_{298}^{°}$ for this reaction and for the condensation of gaseous methanol to liquid methanol.

(c) Calculate the heat of combustion of 1 mole of liquid methanol to H ₂ O( g ) and CO ₂ ( g ).