Determine the enthalpy change, ΔH, for the Haber–Bosch process, in kJ. Use Section 11 of the data booklet.

Suggest why the values obtained in (d)(i) and (d)(ii) differ.

Determine the enthalpy change, ΔH, for the Haber–Bosch process, in kJ. Use Section 11 of the data booklet.

Outline why the value obtained in (b)(i) might differ from a value calculated using ΔH_f data.

Nitrogen dioxide and carbon monoxide react according to the following equation:

NO₂(g) + CO(g) $\rightleftharpoons$ NO(g) + CO₂(g)               ΔH = –226 kJ

Calculate the activation energy for the reverse reaction.

Draw and label an enthalpy level diagram for this reaction.

Explain, giving two reasons, the difference in the values for (c)(i) and (ii). If you did not obtain answers, use −475 kJ for (i) and −600 kJ for (ii).

The diagram shows the Maxwell–Boltzmann distribution and potential energy profile for the reaction without a catalyst.

Annotate both charts to show the activation energy for the catalysed reaction, using the label E_{a (cat)}.

Which is correct for the reaction?

2Al (s) + 6HCl (aq) → 2AlCl₃ (aq) + 3H₂ (g)         ΔH = −1049 kJ

A. Reactants are less stable than products and the reaction is endothermic.

B. Reactants are more stable than products and the reaction is endothermic.

C. Reactants are more stable than products and the reaction is exothermic.

D. Reactants are less stable than products and the reaction is exothermic.

Determine the enthalpy of combustion of this compound, in kJ mol⁻¹, using data from section 11 of the data booklet.

The diagram shows the Maxwell–Boltzmann distribution and potential energy profile for the reaction without a catalyst.

Annotate both charts to show the activation energy for the catalysed reaction, using the label E_{a (cat)}.

What is the enthalpy change, in kJ, of the following reaction?

3H₂ (g) + N₂ (g) $\rightleftharpoons$ 2NH₃ (g)

A. (6 × 391) − [(3 × 436) + 945]

B. (3 × 391) − (436 + 945)

C. −[(3 × 436) + 945] + (3 × 391)

D. −(6 × 391) + [(3 × 436) + 945]

Consider the following reaction:

N₂ (g) + 3H₂ (g) $\rightleftharpoons$ 2NH₃ (g)

Which calculation gives ΔH^Θ, in kJ, for the forward reaction?

A.   2z − y − 3x

B.   y + 3x − 2z

C.   y + 3x − 6z

D.   6z − y − 3x

Methane undergoes incomplete combustion.

2CH₄ (g) + 3O₂ (g) → 2CO (g) + 4H₂O (g)

What is the enthalpy change, in kJ, using the bond enthalpy data given below?

A. [2(1077) + 4(463)] − [2(414) + 3(498)]

B. [2(414) + 3(498)] − [2(1077) + 4(463)]

C. [8(414) + 3(498)] − [2(1077) + 8(463)]

D. [2(1077) + 8(463)] − [8(414) + 3(498)]

Which equation represents the N–H bond enthalpy in NH₃?

A.  NH₃ (g) → N (g) + 3H (g)

B.  $\frac{1}{3}$NH₃ (g) → $\frac{1}{3}$N (g) + H (g)

C.  NH₃ (g) → $\frac{1}{2}$N₂ (g) + $\frac{3}{2}$H₂ (g)

D.  NH₃ (g) → •NH₂ (g) + •H (g)

An allotrope of molecular oxygen is ozone. Compare, giving a reason, the bond enthalpies of the O to O bonds in O₂ and O₃.

Outline why bond enthalpy values are not valid in calculations such as that in (g)(i).

Outline why bond enthalpy values are not valid in calculations such as that in (c)(i).

Under certain conditions, ethyne can be converted to benzene.

Determine the standard enthalpy change, ΔH^Θ, for the reaction stated, using section 11 of the data booklet.

3C₂H₂(g) → C₆H₆(g)

The enthalpy change for the reaction to produce B is −213 kJ. Predict, giving a reason, which product is the most stable.

In which reaction do the reactants have a lower potential energy than the products? 

A. CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g)
B. HBr(g) → H(g) + Br(g) 
C. Na⁺(g) + Cl^-(g) → NaCl(s) 
D. NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)

Determine the enthalpy change for the reaction, in kJ, to produce A using section 11 of the data booklet.

Which statements about bond strength and activation energy are correct for this reaction?

${\mathrm{CH}}_4 \left(\mathrm{g}\right)+2{\mathrm{O}}_2 \left(\mathrm{g}\right)\to {\mathrm{CO}}_2 \left(\mathrm{g}\right)+2{\mathrm{H}}_2\mathrm{O} \left(\mathrm{l}\right)$      $∆H^{⦵}=-891 \mathrm{kJ}$

Ethane-1,2-diol can be formed according to the following reaction.

2CO (g) + 3H₂ (g) $\rightleftharpoons$ HOCH₂CH₂OH (g)

(i) Deduce the equilibrium constant expression, K_c, for this reaction.

(ii) State how increasing the pressure of the reaction mixture at constant temperature will affect the position of equilibrium and the value of K_c.

Position of equilibrium:

K_c:

(iii) Calculate the enthalpy change, ΔH^θ, in kJ, for this reaction using section 11 of the data booklet. The bond enthalpy of the carbon–oxygen bond in CO (g) is 1077kJmol^-1.

(iv) The enthalpy change, ΔH^θ, for the following similar reaction is –233.8 kJ.

2CO(g) + 3H₂(g) $\rightleftharpoons$ HOCH₂CH₂OH (l)

Deduce why this value differs from your answer to (a)(iii).

Outline why ozone in the stratosphere is important.

(i) Suggest why incomplete combustion of plastic, such as polyvinyl chloride, is common in industrial and house fires.

(ii) Phthalate plasticizers such as DEHP, shown below, are frequently used in polyvinyl chloride.

With reference to bonding, suggest a reason why many adults have measurable levels of phthalates in their bodies.

Calculate the enthalpy change of the reaction, ΔH, using section 11 of the data booklet.

(i) Calculate ΔH^θ, in kJ, for this similar reaction below using $\mathrm{\Delta }{H}_{\mathrm{f}}^{\theta }$ data from section 12 of the data booklet. $\mathrm{\Delta }{H}_{\mathrm{f}}^{\theta }$ of HOCH₂CH₂OH(l) is –454.8kJmol^-1.

2CO (g) + 3H₂ (g) $\rightleftharpoons$ HOCH₂CH₂OH (l)

(ii) Deduce why the answers to (a)(iii) and (b)(i) differ.

(iii) ΔS^θ for the reaction in (b)(i) is –620.1JK^-1. Comment on the decrease in entropy.

(iv) Calculate the value of ΔG^θ, in kJ, for this reaction at 298 K using your answer to (b)(i). (If you did not obtain an answer to (b)(i), use –244.0 kJ, but this is not the correct value.)

(v) Comment on the statement that the reaction becomes less spontaneous as temperature is increased.

Sketch an energy profile for the decomposition of calcium carbonate based on your answer to b(i), labelling the axes and activation energy, E_a.

Explain, giving two reasons, the difference in the values for (b)(i) and (ii). If you did not obtain answers, use −475 kJ for (i) and −600 kJ for (ii).

Determine the enthalpy change, ΔH, in kJ. Use section 11 of the data booklet.

Bond enthalpy of CO = 1077 kJ mol⁻¹.

State one reason why you would expect the value of ΔH calculated from the $∆H_f^{\mathrm{⦵}}$ values, given in section 12 of data booklet, to differ from your answer to (d)(i).

Under certain conditions, ethyne can be converted to benzene.

Determine the standard enthalpy change, ΔH^ϴ, for the reaction stated, using section 11 of the data booklet.

                                        3C₂H₂(g) → C₆H₆(g)

Which statement is correct?

A.  ${\mathrm{O}}_3$ bond dissociation occurs at a longer wavelength of light than ${\mathrm{O}}_2$ bond dissociation.

B.  ${\mathrm{O}}_3$ bond dissociation occurs at a higher energy than ${\mathrm{O}}_2$ bond dissociation.

C.  ${\mathrm{O}}_3$ bond lengths are shorter than ${\mathrm{O}}_2$ bond lengths.

D.  ${\mathrm{O}}_3$ bond dissociation occurs at a higher frequency of light than ${\mathrm{O}}_2$ bond dissociation.

Determine the enthalpy change, ΔH, in kJ. Use section 11 of the data booklet.

Bond enthalpy of CO = 1077 kJ mol⁻¹.

Hydrogen gas can be formed industrially by the reaction of natural gas with steam.

                                          CH₄(g) + H₂O(g) → 3H₂(g) + CO(g)

Determine the enthalpy change, ΔH, for the reaction, in kJ, using section 11 of the data booklet.

Bond enthalpy for C≡O: 1077 kJ mol⁻¹

Outline why the value of enthalpy of reaction calculated from bond enthalpies is less accurate.

Calculate the standard enthalpy change, $∆H^{⦵}$, for this reaction using section 12 of the data booklet.

What is the $\mathrm{H}-\mathrm{H}$ bond enthalpy, in $\mathrm{kJ} {\mathrm{mol}}^{-1}$, in the ${\mathrm{H}}_2$ molecule?

$2{\mathrm{H}}_2\left(\mathrm{g}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to 2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right)$

$∆H_{\mathrm{f}}\left({\mathrm{H}}_2\mathrm{O}\right)=x \mathrm{kJ} {\mathrm{mol}}^{-1}$

A.  $x-y+4z$

B.  $\frac{1}{2}\left(x-y+4z\right)$

C.  $x-y+2z$

D.  $\frac{1}{2}\left(x-y+2z\right)$

Hydrogen gas can be formed industrially by the reaction of natural gas with steam.

                                          CH₄(g) + H₂O(g) → 3H₂(g) + CO(g)

Determine the enthalpy change, ΔH, for the reaction, in kJ, using section 11 of the data booklet.

Bond enthalpy for C≡O: 1077 kJ mol⁻¹

Determine the change in enthalpy, ΔH, for the combustion of but-2-ene, using section 11 of the data booklet. 

CH₃CH=CHCH₃(g) + 6O₂ (g) → 4CO₂(g) + 4H₂O (g)

The IR spectrum and low resolution ¹H NMR spectrum of the actual product formed are shown.

Deduce whether the product is A or B, using evidence from these spectra together with sections 26 and 27 of the  data booklet.

Identity of product:

One piece of evidence from IR:

One piece of evidence from ¹H NMR:

Determine the change in enthalpy, ΔH, for the combustion of but-2-ene, using section 11 of the data booklet. 

CH₃CH=CHCH₃(g) + 6O₂ (g) → 4CO₂(g) + 4H₂O (g)

Determine the enthalpy of combustion of the organic product in (b), in kJ mol⁻¹, using data from section 11 of the data booklet.

Determine the standard enthalpy change, $∆H^{⦵}$, for this reaction, using section 11 of the data booklet.

Calculate the enthalpy change of the reaction, ΔH, using section 11 of the data booklet.

Calculate the standard enthalpy change, $∆H^{⦵}$, for this reaction using section 12 of the data booklet.

Determine the standard enthalpy change, $∆H^{⦵}$, for this reaction, using section 11 of the data booklet.

Outline why ozone in the stratosphere is important.

Which equation represents the bond enthalpy for H–Br in hydrogen bromide?

A.  HBr (g) → H⁺ (g) + Br⁻ (g)

B.  HBr (g) → H (g) + Br (g)

C.  HBr (g) → $\frac{1}{2}$H₂ (g) + $\frac{1}{2}$Br₂ (l)

D.  HBr (g) → $\frac{1}{2}$H₂ (g) + $\frac{1}{2}$Br₂ (g)

Explain, using equations, how the presence of ${\text{CCl}}_{\text{2}}{\text{F}}_{\text{2}}$ results in a chain reaction that decreases the concentration of ozone in the stratosphere.

Which combustion reaction releases the least energy per mole of C₃H₈?

Approximate bond enthalpy / kJ mol⁻¹
O=O    500
C=O    800
 C≡O   1000

A.  C₃H₈(g) + 5O₂(g) → 3CO₂(g) + 4H₂O (g)

B.  C₃H₈(g) + $\frac{9}{2}$O₂(g) → 2CO₂(g) + CO (g) + 4H₂O (g)

C.  C₃H₈(g) + 4O₂(g) → CO₂(g) + 2CO (g) + 4H₂O (g)

D.  C₃H₈(g) + $\frac{7}{2}$O₂(g) → 3CO (g) + 4H₂O (g)

Chemistry: Atoms First 2e, https://openstax.org/books/chemistry-atoms-first-2e/pages/9-4-strengths-of-ionic-andcovalent-bonds © 1999–2021, Rice University. Except where otherwise noted, textbooks on this site are licensed under a Creative Commons Attribution 4.0 International License.
(CC BY 4.0) https://creativecommons.org/licenses/ by/4.0/.