Chapter 5: ThermochemistryContent check — Chemistry 2e, Chapter 5: Thermochemistry

(a) C₂H₅OC₂H₅(l)

(b) Na₂CO₃(s)

from the following information:

(i) $2\text{Al}(s)+$ $3{\text{Cl}}_2(g)⟶$ $2{\text{AlCl}}_3(s)$ $\text{Δ}H\text{°}=$ $?$

Use the reactions here to determine the ΔH° for reaction (i):

(ii) $\text{HCl}(g)⟶$ $\text{HCl}(aq)$ $\text{Δ}{H}_{(ii)}^{°}=$ $\mathrm{-74.8}\text{kJ}$

(iii) ${\text{H}}_2(g)+$ ${\text{Cl}}_2(g)⟶$ $2\text{HCl}(g)$ $\text{Δ}{H}_{(iii)}^{°}=$ $\mathrm{-185}\text{kJ}$

(iv) ${\text{AlCl}}_3(aq)⟶$ ${\text{AlCl}}_3(s)$ $\text{Δ}{H}_{(iv)}^{°}=$ $\mathrm{+323}\text{kJ/mol}$

(v) $\text{2Al}(s)+$ $6\text{HCl}(aq)⟶$ $2{\text{AlCl}}_3(aq)+$ $3{\text{H}}_2(g)$ $\text{Δ}{H}_{(v)}^{°}=$ $\mathrm{-1049}\text{kJ}$

Calculate the heat capacity, in joules and in calories per degree, of the following:

(a) 45.8 g of nitrogen gas

(b) 1.00 pound of aluminum metal

A piece of unknown solid substance weighs 437.2 g, and requires 8460 J to increase its temperature from 19.3 °C to 68.9 °C.

(a) What is the specific heat of the substance?

(b) If it is one of the substances found in Table 5.1, what is its likely identity?

The addition of 3.15 g of Ba(OH)₂·8H₂O to a solution of 1.52 g of NH₄SCN in 100 g of water in a calorimeter caused the temperature to fall by 3.1 °C. Assuming the specific heat of the solution and products is 4.20 J/g °C, calculate the approximate amount of heat absorbed by the reaction, which can be represented by the following equation:

Ba(OH)₂·8H₂O(s) + 2NH₄SCN(aq) ⟶ Ba(SCN)₂(aq) + 2NH₃(aq) + 10H₂O(l)

The following sequence of reactions occurs in the commercial production of aqueous nitric acid:
$4{\text{NH}}_3(g)+$ $5{\text{O}}_2(g)⟶$ $4\text{NO}\left(g\right)+$ $6{\text{H}}_2\text{O}\left(l\right)$ $\text{Δ}\text{H}=$ $\mathrm{-907}\text{kJ}$
$2\text{NO}\left(g\right)+$ ${\text{O}}_2(g)⟶$ $2{\text{NO}}_2(g)$ $\text{Δ}\text{H}=$ $\mathrm{-113}\text{kJ}$
$3{\text{NO}}_2+$ ${\text{H}}_2\text{O}\left(l\right)⟶$ $2{\text{HNO}}_3(aq)+$ $\text{NO}(g)$ $\text{Δ}\text{H}=$ $\mathrm{-139}\text{kJ}$

Determine the total enthalpy change for the production of one mole of aqueous nitric acid by this process. Coproducts of the net reaction include water and nitrogen monoxide.

Calculate $\text{Δ}H\text{°}$ for the process
$\text{Sb}\left(s\right)+$ $\frac{5}{2}{\text{Cl}}_2(g)⟶$ ${\text{SbCl}}_5(s)$

from the following information:
$$\begin{array}{l}\\ \text{Sb}\left(s\right)+\frac{3}{2}{\text{Cl}}_2(g)⟶{\text{SbCl}}_3(s)\text{Δ}H\text{°}=\mathrm{-314}\text{kJ}\\ {\text{SbCl}}_3(s)+{\text{Cl}}_2(g)⟶{\text{SbCl}}_5(s)\text{Δ}H\text{°}=\mathrm{-80}\text{kJ}\end{array}$$

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

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

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 white pigment TiO₂ is prepared by the reaction of titanium tetrachloride, TiCl₄, 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 TiO₂(s) under standard state conditions?

Ethylene, C₂H₄, a byproduct from the fractional distillation of petroleum, is fourth among the 50 chemical compounds produced commercially in the largest quantities. About 80% of synthetic ethanol is manufactured from ethylene by its reaction with water in the presence of a suitable catalyst. ${\text{C}}_2{\text{H}}_4(g)+$ ${\text{H}}_2\text{O}\left(g\right)⟶$ ${\text{C}}_2{\text{H}}_5\text{OH}\left(l\right)$

Using the data in the table in Appendix G, calculate ΔH° for the reaction.

Propane, C₃H₈, is a hydrocarbon that is commonly used as a fuel.

(a) Write a balanced equation for the complete combustion of propane gas.

(b) Calculate the volume of air at 25 °C and 1.00 atmosphere that is needed to completely combust 25.0 grams of propane. Assume that air is 21.0 percent O₂ by volume. (Hint: We will see how to do this calculation in a later chapter on gases—for now use the information that 1.00 L of air at 25 °C and 1.00 atm contains 0.275 g of O₂.)

(c) The heat of combustion of propane is −2,219.2 kJ/mol. Calculate the heat of formation, $\text{Δ}{H}_{\text{f}}^{°}$ of propane given that $\text{Δ}{H}_{\text{f}}^{°}$ of H₂O(l) = −285.8 kJ/mol and $\text{Δ}{H}_{\text{f}}^{°}$ of CO₂(g) = −393.5 kJ/mol.

(d) Assuming that all of the heat released in burning 25.0 grams of propane is transferred to 4.00 kilograms of water, calculate the increase in temperature of the water.