DP IB Chemistry: SL

Topic Questions

IBChemistry: SLDPTopic Questions5. Energetics / Thermochemistry5.3 Bond Enthalpy

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First teaching 2014

Last exams 2024

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5.3 Bond Enthalpy

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11 mark

The reaction pathway for a reversible reaction is shown below:q1_5-3_ib_sl_easy_mcq

Which statement is correct?

  • The activation energy of the reverse reaction is +90 kJ mol–1

  • The activation energy of the forward reaction is +20 kJ mol–1

  • The activation energy of the reverse reaction is +20 kJ mol–1

  • The enthalpy change of the forwards reaction is - 70 kJ mol–1

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21 mark

The reaction pathway for a reversible reaction is shown below.q2_5-3_ib_sl_easy_mcq

Which statements are correct? 

I.

The forward reaction is endothermic

II.

The enthalpy change for the backward reaction is –30 kJ mol–1

III.

The activation energy for the forward reaction is +90 kJ mol–1

  • I and II only 

  • I and III only  

  • II and III only 

  • I, II and III

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31 mark

Hydrogen atoms bond covalently to iodine atoms to form hydrogen iodide as shown in the equation below:

H2(g) + I2(g)  →  2HI(g) 

Which statement best describes what is meant by the average HI bond enthalpy?

  • The energy stored in a covalent bond.

  • The energy required to break one covalent bond in the gas phase. 

  • The energy required to break one mole of the HI bonds in the gas phase. 

  • The energy released when two atoms form a covalent bond.

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41 mark

The enthalpy of atomisation of a compound can be calculated using a range of different enthalpy changes. 

Which statement below correctly describes the enthalpy change of atomisation?

  • The energy stored in a covalent bond

  • The energy required to break one covalent bond in the gas phase

  • The energy required to break all bonds in an element  

  • The energy released when two atoms form a covalent bond

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51 mark

Which quantity gives the best indication of the relative strength of the hydrogen bonds between water molecules in the liquid state?

  • Enthalpy changes of vaporisation 

  • Bond dissociation energies 

  • Enthalpy of formation  

  • Activation energy

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61 mark

When a sample of calcium oxide, CaO, is added to dilute hydrochloric acid the temperature rises. Which of the following statements is correct?

  • More bonds are broken than are formed in the reaction

  • More bonds are formed than are broken in the reaction

  • The energy of the bonds broken is greater than of the bonds formed

  • The energy of the bonds broken is less than of the bonds formed

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71 mark

Which is the correct definition of mean bond enthalpy?

  • The amount of energy required to break a specific covalent bond in the gas phase

  • The energy required to break one mole of a specific covalent bond with all chemicals in their standard states

  • The amount of energy required to break a specific covalent bond with all chemicals in their standard states

  • The energy required to break one mole of a specific covalent bond in the gas phase, with all chemicals in their standard states

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81 mark

This energy profile diagram represents the reaction pathway for the following reaction:                                   

Y (g) + Z (g) → W (g) + X (g)

q8_5-3_ib_sl_easy_mcq

 Which statement is true about the reverse reaction, W(g) + X(g) → Y(g) + Z(g)?

  • It will have a negative ΔH 

  • It will have a positive ΔH 

  • It will have a smaller activation energy

  • The temperature of the surroundings increase

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91 mark

Which of the following statements about oxygen and ozone are correct? 

  1. Ozone contains delocalised π bonds
  2. The bond orders of oxygen and ozone are not the same
  3. The bond in oxygen requires radiation of higher energy and longer wavelength than the bond in ozone to break

  • I and II only  

  • I and III only  

  • II and III only 

  • I, II and III

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101 mark

The reaction of hydrogen with iodine to form hydrogen iodide is shown below: 

H2 + I2 → 2HI 

Use the bond energy data given to calculate the enthalpy of reaction, ΔHӨr.

Bond

Energy, kJ mol-1

H-H

432

I-I

149

H-I

295

  • ΔHӨr = 432 + 149 + 295

  • ΔHӨr = 432 + 149 + (2 x 295)

  • ΔHӨr = 432 + 149 - (2 x 295)

  • ΔHӨr = 432 + 149 - 295

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11 mark

In the gas phase, phosphorus pentachloride can be thermally decomposed into gaseous phosphorus trichloride and chlorine.

PCl5  → PCl3 + Cl2

The table below gives the relevant bond energies found in these compounds.

bond

bond energy / kJ mol–1

P–Cl (in both chlorides)

Cl–Cl

x

y

What is the enthalpy change in the decomposition of the reaction?

  • y minus 2 x

  • 2 x minus y

  • 8 x plus y

  • x plus y

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21 mark

Which equation correctly shows how the bond energy for the covalent bond Y–Z can be calculated by dividing ΔH by n?

  • nYZ(g) → nY(g) +begin mathsize 16px style n over 2 end style Z2(g)

  • Z(g) + YZn-1(g) → YZn(g)

  • 2YZn (g) → 2YZn-1(g) + Y2(g)

  • YZn(g) → Y(g) + nZ(g)

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31 mark

The diagram shows the skeletal formula of cyclobutane.
 q3_5-3_mcq_hard_ib-chemistry-sl

The enthalpy change of formation of cyclobutane is +75.1 kJ mol–1, and the enthalpy change of atomisation of graphite is +712 kJ mol–1.

The bond enthalpy of C–H is 414 kJ mol–1 and of H–H is 436 kJ mol–1.

What is the average bond enthalpy of the C–C bond in cyclobutane?

  • 712 blank minus 436 plus 2 left parenthesis 414 right parenthesis plus fraction numerator 75.1 over denominator 4 end fraction

  • 712 blank plus 436 minus 414 minus fraction numerator 75.1 over denominator 4 end fraction

  • 712 blank plus 436 minus 2 left parenthesis 414 right parenthesis minus fraction numerator 75.1 over denominator 4 end fraction

  • 712 blank plus 436 minus 2 left parenthesis 414 right parenthesis minus 75.1

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41 mark

Butane can be produced by the hydrogenation of buta-1,3-diene.

C4H6 (g) + 2H2 (g) → C4H10 (g)                 ΔH = -248 kJ mol-1

Bond

C-C

C-H

H-H

Mean bond enthalpy / kJ mol-1

346

414

436

Using the information, which calculation shows the bond enthalpy for the C=C bond in buta-1,3-diene?

  • -248 - ( 2 x 436) + (2 x 346) + (4 x 414)

  • -124 - 436 + 346 + (2 x 414)

  • (2 x 346) + (4 x 414) + 248 - (2 x 436)

  • 346 + (2 x 414) + 124 - 436

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51 mark

The equations to form methane and propane from their gaseous atoms are:

C (g) + 4H (g) → CH4 (g)              ΔHr = -1656 kJ mol-1

3C (g) + 8H (g) → C3H8 (g)           ΔHr = -4004 kJ mol-1

What is the bond enthalpy of a C-C bond?

  • begin mathsize 16px style fraction numerator negative 4004 blank plus blank 2 blank cross times blank left parenthesis 1656 right parenthesis over denominator 3 end fraction end style

  • 2002 - 1656

  • 1656 - 2002

  • begin mathsize 16px style fraction numerator negative 4004 blank minus blank 2 blank cross times blank left parenthesis 1656 right parenthesis over denominator 3 end fraction end style

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61 mark

Ultraviolet radiation is split into three regions:

  • UV A (wavelength 400 - 320 nm)
  • UV B (wavelength 320 - 280 nm)
  • UV C (wavelength < 280 nm)

High energy photons are present in the solar spectrum at high altitude. The maximum wavelength of a photon that has enough energy to break the O=O bond in oxygen is 240 nm, which is in the UV C region of ultraviolet radiation..

The energy per mole required to break an O=O bond can be calculated using the following equation:

 begin mathsize 16px style fraction numerator B o n d blank e n e r g y blank p e r blank m o l e over denominator A v o g a d r o apostrophe s blank c o n s t a n t end fraction end style= Energy per bond

Using the supplementary equations c = νλ and E = hν, which is the correct calculation to determine the bond energy of an O=O in kJ mol-1?

Avogadro’s constant = 6.02 x 1023

Planck’s constant = 6.63 x 10-34 J s

Speed of light = 3.00 x 108 m s-1

  • begin mathsize 16px style fraction numerator 6.63 blank cross times blank 3.00 blank cross times blank 6.02 blank cross times blank 10 over denominator 2.4 end fraction end style

  • fraction numerator 6.63 blank cross times blank 3.00 blank cross times blank 6.02 blank cross times blank 10 to the power of 4 over denominator 2.4 end fraction

  • begin mathsize 16px style fraction numerator 6.63 blank cross times blank 3.00 blank cross times blank 6.02 blank cross times blank 10 to the power of negative 3 end exponent over denominator 2.4 end fraction end style

  • begin mathsize 16px style fraction numerator 6.02 blank cross times blank 2.4 blank cross times blank 10 to the power of 42 over denominator 6.63 blank cross times blank 3.00 blank end fraction end style

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71 mark

Which of the following statements about the average bond enthalpy of the halogens are correct?

  1. Fluorine has the highest average bond enthalpy
  2. Average bond enthalpy generally decreases as the size of the atoms increases
  3. In general, increased shielding results in a lower bond enthalpy

  • I and II only  

  • I and III only  

  • II and III only 

  • I, II and III

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81 mark

What is the correct order to show the decreasing strength of the F-H, N-H and O-H bonds?

  • N-H > O-H > F-H 

  • O-H > N-H > F-H

  • F-H > N-H > O-H 

  • F-H > O-H > N-H 

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91 mark

Water has two different bond enthalpies for the two O-H bonds that it contains:

H2O (g) → H (g) + OH (g)             ΔH = +502 kJ mol-1

OH (g) → H (g) + O (g)                 ΔH = +427 kJ mol-1

The average O-H bond enthalpy from an accepted data table is 463 kJ mol-1.

Which calculation correctly shows the percentage difference between the average O-H bond enthalpy of water and the data table average bond enthalpy value?

  • 100 divided by open parentheses fraction numerator 502 blank plus blank 427 over denominator 2 blank cross times blank 463 end fraction minus 1 close parentheses

  • 100 cross times open parentheses fraction numerator 502 blank plus blank 427 over denominator 2 blank cross times blank 463 end fraction minus 1 close parentheses

  • 100 cross times open parentheses fraction numerator 2 blank cross times blank 463 over denominator 502 blank plus blank 427 end fraction minus 1 close parentheses

  • 100 cross times open parentheses fraction numerator 502 blank plus blank 427 over denominator 2 blank cross times blank 436 end fraction minus 1 close parentheses

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101 mark

Some of the reactions involved in the formation and depletion of ozone are:

  1. O2 → 2O●
  2. O2 + O● → O3
  3. O3 + O● → 2O2

Which reactions are exothermic?

  • I and II only  

  • I and III only  

  • II and III only 

  • I, II and III

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11 mark

The standard enthalpy change, ΔHӨ, for the following reaction is -246 kJ. 

N2(g)  +  3F2(g)  →  2NF3(g)     

The bond energy of  N≡N is 945 kJ mol-1 and F–F is 159 kJ mol-1 

What is the bond energy of the N–F bond?

  • begin mathsize 14px style fraction numerator 246 space minus space left parenthesis 945 space plus space left parenthesis 3 space cross times space 159 right parenthesis right parenthesis space over denominator 6 end fraction end style

  • begin mathsize 14px style fraction numerator negative 246 space plus space left parenthesis 945 space plus space left parenthesis 3 space cross times space 159 right parenthesis right parenthesis over denominator 6 end fraction end style

  • begin mathsize 14px style fraction numerator 246 space plus space left parenthesis 945 space plus space left parenthesis 3 space cross times space 159 right parenthesis right parenthesis over denominator 6 end fraction end style

  • begin mathsize 14px style 246 space plus space left parenthesis 945 space plus space left parenthesis 3 space cross times space 159 right parenthesis right parenthesis space end style

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21 mark

The complete combustion of ethyne, C2H2, is shown in the equation below. 

H−C≡C−H + 2½ O═O  →  H−O−H + 2O═C═O 

Using the average bond enthalpies given in the table, what is the enthalpy change of combustion of ethyne?

 

bond

average bond

enthalpy / kJ mol-1

C−H

a

C≡C

b

O═O

c

C═O

d

O−H

e

  • begin mathsize 14px style left parenthesis 2 straight e plus 4 straight d right parenthesis minus left parenthesis 2 straight a plus straight b plus 2 ½ straight c space right parenthesis end style

  • begin mathsize 14px style left parenthesis 2 straight a plus straight b plus 2 ½ straight c space right parenthesis minus left parenthesis negative 2 straight e minus 4 straight d right parenthesis end style

  • begin mathsize 14px style left parenthesis 2 straight a plus straight b plus 2 ½ straight c space right parenthesis minus left parenthesis 2 straight e plus 4 straight d right parenthesis end style

  • begin mathsize 14px style negative straight e minus straight d plus left parenthesis 2 straight a plus straight b plus 2 ½ straight c space right parenthesis end style

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31 mark

Compound R into compound T, it was found that the reaction proceeded by way of compound S, which could be isolated. The following steps were involved. 

R → S;  ΔH is positive

S → T; ΔH is negative

Which reaction profile fits these data?q3_5-3_ib_sl_easy_mcq

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41 mark

The reaction pathway for an endothermic reaction is shown.q4_5-3-ib_sl_medium_mcq

 Which arrow represents the activation energy for the reverse reaction?

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51 mark

The reaction pathway shows the energies of the reactants, the products and the transition state of a reaction.q5_5-3_ib_sl_medium_mcq

Which expression correctly represents how to calculate the activation energy of the forward reaction?

  • E3 – E2

  • E2 – E1

  • E2 – E3

  • E1 – E2

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61 mark

The incomplete combustion of methanol can produce carbon monoxide and water: 

 q6_5-3_ib-sl_medium_mcq

Some enthalpy data is given in the table.

 

C-H

C-O

O-H

O=O

C=O
Mean bond dissociation enthalpy / kJ mol−1

414

358

463

498

804

 

What is the enthalpy change for this incomplete combustion of methanol?

  • (414 + 358 + 463 + 498) - (463 + 804)

  • (4 x 463 + 804) - (3 x 414 + 358 + 463 + 498)

  • (4 x 414 + 358 + 498) - (4 x 463 + 804)

  • (3 x 414 + 358 + 463 + 498) - (4 x 463 + 804)

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71 mark

Which of the following statements about bond enthalpy are true? 

  1. A bond enthalpy may be inaccurate when compared to data tables because it is not an average value
  2. Average bond enthalpies are valid for all states of matter
  3. Bond enthalpies may be inaccurate as they do not account for intermolecular forces

  • I and II only  

  • I and III only  

  • II and III only 

  • I, II and III

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81 mark

Four possible reactions (A, B, C and D) of the following equation are measured at the same temperature. 

                                                X (g) + Y (g) → Z (g) 

Which reaction pathway diagram shows the reaction occurring rapidly with an overall negative enthalpy value?q8_5-3_ib_sl_medium_mcq

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91 mark

Which combination about bond breaking and bond formation energy changes is correct?

 

Bond breaking

Bond formation

A

endothermic

endothermic

B

endothermic

exothermic

C

exothermic

endothermic

D

exothermic

exothermic

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101 mark

Which reactions are involved in maintaining the concentration of ozone in the upper atmosphere? 

  1. O3 → O2 + O●
  2. O2 → 2O●
  3. O2 + O● → O3

  • I and II only  

  • I and III only  

  • II and III only 

  • I, II and III

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