Syllabus Edition

First teaching 2023

First exams 2025

|

Energy Cycles in Reactions (HL IB Chemistry)

Exam Questions

5 hours79 questions
1a1 mark

State Hess’s Law.

1b1 mark

State the type of system in which the total amount of matter present is always constant. 

1c1 mark

Using the image below, construct an equation that can be used to determine ΔHr from ΔH1 and  ΔH2.

5-2-ib-sl-sq-easy-q1c-hesss-law-cycle

1d3 marks

Complete the following Hess’s Law cycle for the decomposition of copper carbonate.

5-2-ib-sl-sq-easy-q1d-hesss-law-cycle-cuco3

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2a2 marks

Define standard enthalpy of formation, ΔHf

2b
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8 marks

Write an equation to show the enthalpy of formation of 1 mole of the following compounds. Include state symbols in your equations. 

Methanol, CH3OH ………………………………..

Carbon dioxide, CO………………………………..

Ethane, C2H………………………………..

2c3 marks

Using the equations given, construct a Hess’s Law cycle for the following reaction. Include the values for ΔHf  in your cycle.  

BaCl2 (s) + Zn (s) → Ba (s) + ZnCl(s)

Ba (s) + Cl2 (g) → BaCl(s)      ΔHf = -858.6 kJ mol-1

Zn (s) + Cl2 (g) → ZnCl2 (s)         ΔHf = -415.1 kJ mol-1

2d
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3 marks

Calculate the enthalpy of reaction, ΔHrfor the reaction given in part (c).

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3a4 marks

Aluminium oxide reacts with magnesium to form magnesium oxide and aluminium in a displacement reaction via the following reaction.Construct a Hess’s Law cycle for this reaction

Al2O3 (s) + 3Mg (s) → 3MgO (s) + 2Al (s)

 

Enthalpy of formation Enthalpy of formation (kJ mol-1)
ΔHf (Al2O3) -1675.7 
ΔHf (MgO) -601.7 
ΔHf (Mg)  
ΔHf (Al)  

3b1 mark

Outline why no values are listed for Al (s) and Mg (s) in the table given in part (a).

3c
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2 marks

Calculate the enthalpy change of reaction, ΔHr, for the reaction in part (a).

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4a3 marks

Determine the enthalpy change of reaction, ΔHr, for the following equations if they are reversed. 

2Na + Cl2 → 2NaCl           ΔHr = -790 kJ ……………………….

C2H+ H2 → C2H6               ΔHr = -65.6 kJ ………………………

2H2O → 2H+ O2             ΔH= +571 kJ ……………………….

4b
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1 mark

Using the information given in part (a), determine the enthalpy change for the following reaction.

2C2H4 + 2H2 → 2C2H6

4c
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1 mark

Using the information in the table, deduce which equation should be reversed to determine the enthalpy change for the following reaction. 

SiO2 + 3C → SiC + 2CO

Equation number  Equation Enthalpy change (kJ)
1 Si + O2 → SiO2 -911
2 2C + O2 → 2CO -211
3 Si + C → SiC -65.3

4d
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2 marks

Use the information in part (c) to produce an overall cancelled down equation which can be used to determine the overall enthalpy change for the following reaction. 

SiO2 + 3C → SiC + 2CO

4e
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2 marks

Deduce the overall enthalpy change, in kJ, using the information in part (c) for the reaction SiO2 + 3C → SiC + 2CO

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5a1 mark

State the equation required to calculate the enthalpy change of reaction, ΔHr, given enthalpy of formation, ΔHf, data. 

5b
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3 marks

Using section 13 in the data booklet and the data in the table calculate the enthalpy change of reaction, ΔHr, for the following reaction.

SO2 (g) + 2H2S (g) → 3S (s) + 2H2O (l) 

  SO2 (g) H2S (g)
ΔHf (kJ mol-1 -297 -20.2
5c2 marks

Show how the equations can be used to produce an alternative route for this reaction.

C2H4 + H2 → C2H6

  ΔH (kJ mol-1)
C2H4 + 3O2 → 2CO2 + 2H2O -1411
C2H6 + 3½O2 2CO(g) + 3H2O -1560
H2 + ½O2 → H2O -285.8

5d
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1 mark

Calculate ΔH

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6a1 mark

State the formula for calculating the standard enthalpy change of reaction, ΔHr, using bond energies.

6b
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4 marks

Use section 12 of the data booklet to calculate the enthalpy change, in kJ mol-1, for the following reaction.    

Cl2 + H2 → 2HCl 

6c1 mark

State whether the energy change for the reaction in part (b) is endothermic or exothermic.

6d
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4 marks

Using section 12 of the data booklet, calculate the enthalpy change of reaction, ΔHr, in kJ mol-1 for the following reaction.

CH4 + Cl2 → CH3Cl + HCl 

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7a2 marks

Using molecular formulae, write the equation for the reaction of ethene with water to form ethanol.

7b
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4 marks

Using section 12 in the data booklet calculate the enthalpy change of reaction, ΔHr, for the reaction of ethene with water. 

7c1 mark

Define bond dissociation energy.

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8a3 marks

Write one equation to represent each the following changes:


Atomisation of sodium ………………………………………………………………….


First ionisation energy of magnesium ………………………………………………………………….


First electron affinity of chlorine ………………………………………………………………….

8b2 marks

Give the definition of the term enthalpy of lattice formation.



8c3 marks

Study the following Born-Haber cycle.

img-2510

State the enthalpy changes for the following steps: 

Step 1 ………………………………………………………………………………………………..

Step 3 ………………………………………………………………………………………………..

Step 4 ………………………………………………………………………………………………..

8d3 marks

The enthalpy of lattice formation of potassium fluoride and caesium fluoride is -829 kJ mol-1 and -759 kJ mol-1 respectively.

With reference to the ions in the structure, explain why the enthalpy of lattice formation i
s more exothermic for potassium fluoride.

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9a3 marks

State the definition of electron affinity, ΔHea.

9b2 marks

Electron affinities can be represented using equations.

i)
State the equation which represents the first electron affinity of oxygen.
[1]
ii)
State the equation which represents the second electron affinity of oxygen.

[1]

9c2 marks

The first and second electron affinities of oxygen are shown in the table below.

First electron affinity of O -141 kJ mol-1 Exothermic
Second electron affinity of O +753kJ mol-1 Endothermic

State why the second electron affinity of oxygen is an endothermic process.

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10a2 marks

The incomplete Born-Haber cycle for silver fluoride, AgF, is shown below.

4f157c5f-edcc-4420-a0a6-eb114baa5c79

Complete the Born Haber cycle. 

10b
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2 marks

Use the Born-Haber cycle in part a) and sections 8 and 11 in the data booklet to determine the enthalpy changes, in kJ mol-1, of the following.

The enthalpy of atomisation of silver, ΔHat(Ag) , is +289 kJ mol-1

The enthalpy of atomisation of fluorine, ΔHat(F) , is +79 kJ mol-1

ΔHat(Ag) + ΔHie(Ag) ................................................................

ΔHat(F) + ΔHea(F) ................................................................

10c
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3 marks

Use your answer to part b) and the lattice enthalpy of silver fluoride, ΔHlatt(AgF) , in section 18 in the data booklet to determine the enthalpy of formation of silver fluoride, ΔHf(AgF), in kJ mol-1

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1a3 marks

Nitrogen oxides produced by combustion are largely nitrogen monoxide or nitrogen dioxide.

Draw Lewis diagrams for nitrogen monoxide and nitrogen dioxide and use the diagrams to explain the meaning of the term free radical.

1b2 marks

Platinum and rhodium are found in catalytic converters and facilitate the conversion of Carbon monoxide and nitrogen monoxides to nitrogen and carbon dioxide.

Write an equation for the reaction and state the changes in oxidation state for each carbon and nitrogen.

1c4 marks

Use your answer to part (c) and the bond enthalpy data given in Table 1 to determine the enthalpy change for the reaction between carbon monoxide and nitrogen monoxide.

Table 1

C≡O

N=O

N≡N

C=O

1077 kJ mol-1

587 kJ mol-1

945 kJ mol-1

804 kJ mol-1

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2a3 marks

Define the term standard enthalpy of formation, ΔHϴf.

2b2 marks

State Hess’s Law.

2c2 marks

The following equation represents the second step in the extraction of titanium, using the Kroll process:

TiCl4 (g) + 4Na (l) → 4NaCl (s) + Ti (s)

Use the standard formation data shown in Table 1 to calculate the enthalpy change for the reaction, ΔHϴr.

Table 1 

 

TiCl4 (g)

Na (l)

NaCl (s)

Ti (s)

ΔHϴf (kJ mol-1)

-720

+3

-411

0

 

2d3 marks

Construct a Hess’s Law cycle for the reaction of calcium fluoride, CaF2 (s) , and sulfuric acid, H2SO4 (aq).

CaF2 (s) + H2SO4 (aq) → 2HF (g) + CaSO4 (s)

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3a3 marks

Define the term standard enthalpy of combustion, ΔHϴc.

3b2 marks

Write an equation for the complete combustion of propanol, CH3CH2CH2OH (l).

3c3 marks

Construct a Hess’s Law cycle for the complete combustion of propanol.

Table 1

 

CH3CH2CH2OH (l)

O2 (g)

CO(g)

H2O (l)

ΔHϴf (kJ mol-1)

-303

0

-394

-286

 

3d3 marks

Use the data given in Table 1 in part (d) to calculate the enthalpy change of the reaction, ΔHϴr.

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4a2 marks

Urea can be used as a fertiliser and is manufactured by the reaction of ammonia and carbon dioxide via the following equation. 

2NH3 (g) + CO2 (g) → NH2CONH2 (s) + H2O (l)

Using the data in Table 1 calculate the enthalpy change for the formation of urea, ΔHrө.

Table 1

 

NH3 (g)

NH2CONH2 (s)

CO2  (g)

H2O (l)

ΔHϴf (kJ mol-1)

-46.2

-333.2

-393.5

-285.8

4b3 marks

Ammonia reacts with oxygen to produce steam and nitrogen(II) oxide. Draw a Hess’s Law cycle which could be used to calculate the enthalpy change of the reaction using formation data.

4c3 marks

Use Hess’s Law and the information below to calculate the enthalpy change, ΔHϴr, for the conversion of one mole of ethene and one mole of hydrogen to one mole of ethane. 

C2H4 (g) + 3O2 (g) → 2CO2 (g) + 2H2O (l)                  ΔHϴr = -1411 kJ mol-1

C2H6 (g) + 3.5O2 (g) → 2CO2 (g) + 3H2O (l)               ΔHϴr = -1560 kJ mol-1

H2 (g) + 0.5O2 (g) → H2O (l)                                       ΔHϴr = –286 kJ mol-1

4d3 marks

Use Hess’s Law and the information below to calculate the enthalpy change for the conversion of one mole of solid carbon into carbon monoxide.

C (s) + O2 (g) → CO(g)                    ΔHϴr = - 393.5 kJ mol-1

CO (g) + ½O2 (g)  → CO(g)            ΔHϴr = - 283.5 kJ mol-1

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5a2 marks

Define the term standard enthalpy of reaction, ΔHϴr.

5b4 marks

Use Hess’s Law and the information below to calculate the enthalpy change, ΔHϴr, for the conversion of methane and ammonia to form hydrogen cyanide and hydrogen.

N2 (g) + 3H2 (g) → 2NH3 (g)                           ΔHϴr = -91.8 kJ

C (s) + 2H2 (g) → CH4 (g)                                        ΔHϴr = -74.9 kJ

H2 (g) + 2C (g) + N2 (g) → 2HCN (g)              ΔHϴr = 270.3 kJ

5c3 marks

Using your answer to part (b) draw a reaction profile diagram for the reaction outlined.

5d1 mark

Draw the Lewis structure for hydrogen cyanide, HCN.

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6a1 mark

Butane, C4H10,  is typically used as fuel for cigarette lighters and portable stoves, a propellant in aerosols, a heating fuel, a refrigerant, and in the manufacture of a wide range of products.

Write an equation for the complete combustion of butane.

6b4 marks

Determine the enthalpy of formation of butane, C4H10 , using the enthalpy of combustion data below.

C (s) + O2 (g) → CO2 (g)                                            ΔHϴf = -394 kJ           

H2 (g) + 0.5O2 (g) → H2O (l)                                       ΔHϴf = -286 kJ

C4H10 (g) + 6.5O2 (g) → 4CO2 (g) + 5H2O (l)             ΔHϴf = -2878 kJ

6c3 marks

Butane can be formed from the hydrogenation of butene. Using the data in Table 1, determine a value for the enthalpy of formation.

Table 1

Bond

Mean Bond Enthalpy ΔHϴ (kJ mol-1)

C-C

346

C-H

414

H-H

436

C=C

614

 

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7a3 marks

Enthalpy changes can be found using bond enthalpy data. Some bond enthalpy values are shown below in Table 1.

Table 1

Bond

Mean Bond Enthalpy ΔHϴ (kJ mol-1)

C-C

346

C-H

414

H-H

436

 

 The balanced equation for the reaction between methane and propane is

CH4 (g) +  CH3CH2CH3 (g) → CH3CH2CH2CH3 (g) + H2 (g)

Use the equation and bond enthalpy data to calculate the enthalpy change for the above reaction.                                  

7b1 mark

Define the term average bond enthalpy.

7c3 marks

Enthalpy changes can be found using bond enthalpy data. Some bond enthalpy values are shown below in Table 2. 

Table 2

Bond

Mean Bond Enthalpy ΔHϴ (kJ mol-1)

C=C

614

C-H

414

O-H

463

C=O

804

O=O

498

 

The balanced equation for the combustion of ethene is

C2H4 (g) + 3O2 (g) → 2CO2 (g) + 2H2O (l)

Use the equation and bond enthalpy data to calculate the enthalpy of combustion of ethene.

7d1 mark

Bond enthalpies can be found using Hess’s Law or from experimental data.

Outline the difference between the two ways of finding bond enthalpy.

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8a1 mark

Use the energy level diagram to determine the activation energy, Ea, for the given reaction in Figure 1.

Figure 1

5-3-ib-chemistry-sq-q4a-medium

8b3 marks

Ethene can be hydrated via the following reaction:

C2H4 (g) + H2O (g) → C2H5OH (g)

Table 1

Bond

C-C

C=C

C-H

C-O

O-H

Mean bond enthalpy (kJ mol-1)

346

614

414

358

463

 

Use the data in Table 1 to calculate the enthalpy change for the hydration of ethene.

8c2 marks

Explain why the value to your answer to part (b) is different from the data book value for the hydration of ethene.

C2H4 (g) + H2O (g) → C2H5OH (g)

8d3 marks

Table 2 below has some enthalpy data for a different chemical reaction. Hydrazine, N2H4 can react with hydrogen peroxide in an exothermic reaction, as shown below.

N2H4(g) + 2H2O2 → N2(g) + 4H2O(g)                          ΔHϴr = -789 kJ mol-1

The structure of hydrazine is shown in Figure 1.

Figure 1

5-3-ib-chemistry-sq-q4d-medium 

Table 2

Bond

Mean Bond Enthalpy ΔHϴ (kJ mol-1)

N-N

+158

N≡N

+945

O-H

+463

O-O

+144

 

Using the reaction equation and the data in the table above, calculate the value of the N-H bond in hydrazine.

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9a4 marks

Pure crystals of lithium fluoride are used in X-ray monochromator.

q1a_15-1_sq_medium_ib_hl

i)
Define the term enthalpy of atomisation.
[1]
ii)
Explain why the enthalpy of atomisation of fluorine is positive.
[1]
iii)
Complete the Born–Haber cycle for lithium fluoride by adding the missing species on the lines.
[2]
9b5 marks

Use the data in the following table and your completed Born–Haber cycle from part (a) to answer the questions below.


Name of enthalpy change

Energy change / kJ mol-1

Li (s) → Li (g)

+216

Li (g) → Li+ (g) + e-

+520

F2 (g) → 2F (g)

+158

F (g) + e- → F- (g)

-348

Li (s) + ½F2 (g) → LiF (s)

-594

i)
Calculate the enthalpy of lattice formation of lithium fluoride.
[2]
ii)
Explain and justify how the enthalpy of lattice formation of LiBr compares with that of LiF. You must refer to the size of the ions in your answer.
[3]

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10a5 marks

Calcium chloride has many uses including as an agent to lower the freezing point of water. It is very effective for preventing ice formation on road surfaces and as a deicer.

i)
Define the term ionisation energy.
[2]
ii)
Explain why the second ionisation energy of calcium is greater than the first ionisation energy.
[3]
10b2 marks

Describe the structure and bonding in calcium chloride.

10c2 marks

The Born-Haber cycle for CaCl2 is shown:

q2c_15-1_sq_medium_ib_hl

Using Section 9 in the Data Booklet and the following information, calculate the enthalpy change for the following conversions. 

  • ΔHθIE2 Ca = 1145 kJ mol-1                       
  • ΔHθat Ca = 178 kJ mol-1
  • ΔHθBE Cl2 = 242 kJ mol-1
i)
Ca (s) → Ca2+ (g) + 2e-
[1]
ii)
Cl2 (g) + 2e- → 2Cl- (g)
[1]
10d2 marks

Using Section 16 of the Data Booklet, calculate the value for the enthalpy of formation for calcium chloride, ΔHθf CaCl2

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11a5 marks

This question is about fluorine and the associated energy changes when it reacts with magnesium to form magnesium fluoride.

i)
Define the term electron affinity.
[2]
ii)
Using Sections 9 and 12 in the Data Booklet and showing your working, determine the electron affinity of a fluorine atom, ΔHθEA 
[3]
 

Name of enthalpy change

Energy change (kJ mol-1)

Enthalpy of atomisation of magnesium

+150

Second ionisation energy of magnesium

+1450

Enthalpy of formation of magnesium fluoride

-642

Lattice enthalpy of formation of magnesium fluoride

-2493

11b2 marks

Suggest why the first electron affinity of fluorine is an exothermic change.

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1a2 marks

Vanadium is commonly found in different ores such as magnetite, vanadinite and patronite. The vanadium is commonly extracted from these ores by reduction and displacement.

Vanadium can be extracted by the reduction of vanadium pentoxide, V2O5, with calcium at high temperatures, according to the following equation.

V2O5 (s) + 5Ca (s) → 2V (s) + 5CaO (s)

The enthalpy of formation of vanadium pentoxide is -1560 kJ mol-1 and the standard enthalpy change for the reaction is -1615 kJ mol-1


Construct a Hess’s Law cycle for this reaction.

1b
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3 marks

Use the data in part a) to calculate the enthalpy of formation, ΔHf, of calcium oxide in kJ mol-1

1c2 marks
Define standard enthalpy of neutralisation, ΔHneut

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2a3 marks

The compound diborane, B2H6, is used as a rocket fuel. The equation for the combustion of diborane is shown below.


B2H6 (g) + 3O2 (g) → B2O3 (s) + 3H2O (l)

Calculate the standard enthalpy change of this reaction using the following data

  1. 2B (s) + 3H2 (g) → B2H6 (g)          ΔH = 36 kJ mol-1
  2. H2 (g) + ½O2 (g) → H2O (l)          ΔH = -286 kJ mol-1
  3. 2B (s) + 1½O2 (g) → B2O3 (s)       ΔH = -1274 kJ mol-1
2b1 mark

Ethyne, C2H2, is a useful gas as it gives a high temperature flame when burnt with oxygen. State the equation for the combustion of ethyne gas.

2c3 marks

Use your answer to part b) to construct a Hess's Law cycle for the combustion of ethyne gas.

2d
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3 marks

Use section 13 in the data booklet to determine the enthalpy of combustion, ΔHc, of ethyne gas. 

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3a3 marks

Coal gasification converts coal into a combustible mixture of carbon monoxide and hydrogen known as coal gas, in a gasifier. 

H2O (l) + C (s) → CO (g) + H2 (g) 

Using the following equations, calculate the enthalpy change of reaction, ΔHr, in kJ for cola gasification. 

I. 2C (s) + O2 (g) → 2CO (g)            ΔH = -222 kJ

II. 2H(g) + O2 (g) → 2H2O (g)        ΔH = -484 kJ

III. H2O (l) → H2O (g)                       ΔH = +44 kJ

[3]
3b
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3 marks

This coal gas can be used as a fuel as the following equation shows.

CO (g) + H2 (g) + O2 (g) → CO2 (g) + H2O (g) 

Calculation the enthalpy change of reaction, ΔHr, in kJ for this combustion reaction from the following equations.

I. 2C (s) + O2 (g) → 2CO (g)       Δ= -222 kJ

II. C (s) + O2 (g) → CO2 (g)         Δ= -394 kJ

III. 2H2 (g) + O2 (g) → 2H2O (g) Δ= -484 kJ

3c2 marks

Blending amounts of alternative fuel with conventional fuel is one way to replace petroleum. A fuel blend of 51% to 83% ethanol and the remaining being gasoline is known as E85.

If the fuel blend is vaporised before combustion, predict whether the amount of energy released would be greater, less or the same. Explain your answer.

3d
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3 marks

Use sections 7 and 14 of the Data booklet to calculate the following.

i)
The amount, in moles, of ethanol in 1 kg of E85 containing 60% ethanol.

[2]

ii)
The energy released, in kJ, by ethanol if 1 kg of E85 is burnt.

[1]

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4a3 marks

Strontium salts have a number of applications such as fireworks, flares, glow in the dark paint and toothpaste for sensitive teeth. The strontium required for these salts can be extracted from the ore strontia, SrO, by displacement with powdered aluminium in a vacuum.

i)
Write a balanced symbol equation, including state symbols, for the reaction of strontia with aluminium.
[2]

ii)
State the role of the aluminium in this reaction.
[1]
4b
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3 marks

The standard enthalpy change for this extraction of strontium is 99.3 kJ mol-1 and the standard enthalpy of formation of aluminium oxide is -1676.7 kJ mol-1

Use this information to calculate the standard enthalpy of formation, ΔHf, in kJ mol-1 of strontia.

4c
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3 marks

Manganese is too brittle for use as a pure metal, so it is often alloyed with other metals. Manganese is used in steel to increase the strength and resistance to wear. Manganese steel (13% Mn) is extremely strong and used for railway tracks, safes and prison bars. Alloys of 1.5% manganese with aluminium are used to make drinks cans due to the improved corrosion resistance of the alloy.

Manganese is extracted from different ores by reduction with carbon monoxide.

Mn2O3 (s) + 3CO (g) → 2Mn (s) + 3CO2 (g)

 

The enthalpy of formation, ΔHf, of Mn2O(s) is −971 kJ mol-1. Use this information and section 13 of the data booklet to calculate the enthalpy change of reaction, ΔHr, in kJ mol-1

4d3 marks

The reaction in part c) reaches equilibrium at high temperatures.

Use your answer to part c) to explain how temperature can be altered to increase the yield of
the reaction and explain the effect that this would have on the rate of reaction.

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5a2 marks

Define the term average bond enthalpy.

5b
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3 marks

Determine the bond dissociation energy, in kJ mol-1, for one mole of O−F bonds using the following equation and section 12 of the data booklet. Give your answer to 3 significant figures. 

F(g) + ½O(g) → OF2 (g)    ΔHr = +28 kJ mol-1

5c2 marks

The reaction of ethanoyl chloride, CH3COCl , and ethanol form an ester. State the equation for this reaction.

5d
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2 marks

Use section 12 in the data booklet to deduce the energy required, in kJ mol-1, to break the bonds.

5e
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3 marks

Deduce the energy released, in kJ mol-1, when the bonds are formed and therefore the enthalpy change for the reaction.

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6a
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2 marks

Methane reacts violently with fluorine to form carbon tetrafluoride and hydrogen fluoride

Formulate the equation for this reaction. 

6b
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4 marks

Use your answer to part a) and section 12 of the data booklet to calculate the following:

i)
The energy required, in kJ, to break the bonds for the reaction between methane and fluorine.
[1]
ii)
The energy released, in kJ, to form the bonds for the reaction between methane and fluorine.
[1]
iii)
The enthalpy change, ΔHr, in kJ mol-1 for this reaction. 
[2]

6c3 marks

Sketch a labelled energy diagram for the reaction of methane and fluorine.

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7a2 marks

Hydrazine has the formula N2H4 and is used as a rocket fuel (e.g. for the Apollo moon rockets). It burns in the following reaction for which the enthalpy change is -583 kJ mol-1.

N2H4 (g) + O2 (g) → N2 (g) + 2H2O (g)


Sketch the Lewis structure of hydrazine, N2H4.

7b
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3 marks

Use section 12 of the Data booklet and the information in part a) to deduce the bond enthalpy, in kJ mol-1, for the N-N bond.

7c1 mark

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

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8a2 marks

Lattice enthalpies can be determined experimentally using a Born–Haber cycle and theoretically using calculations based on electrostatic principles.

The experimental lattice enthalpies of magnesium chloride, MgCl, calcium chloride, CaCl2 , strontium chloride, SrCl2 , and barium chloride, BaCl2 are given in section 16 of the data booklet. Explain the trend in the values. 

8b2 marks

Explain why strontium chloride, SrCl2 , has a much greater lattice enthalpy than rubidium chloride, RbCl.

8c
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3 marks

Strontium is used as a red colouring agent in fireworks as it provides a very intense red colour. Use sections 9 and 16 to calculate the enthalpy of atomisation for chlorine in strontium chloride.

Enthalpy change Enthalpy change (kJ mol-1)
Sr (s) → Sr (g) 164.0
Sr (s) + Cl2 (g) → SrCl2 (s) -828.9
Sr+ (g) → Sr2+ (g) + e- 1064.3

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9a3 marks

The incomplete Born-Haber cycle for sodium selenide is shown below. 

State the equations for processes 1, 2 and 3. 

239d5e33-5fba-4b56-8a32-4882bf910f8f

9b3 marks

If sulfur is used as opposed to selenium in the lattice, what would you expect to happen to the value of the enthalpy of lattice dissociation. Explain your answer.

9c
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Use section 9 in the data booklet and the information in the table to calculate the lattice enthalpy of aluminium oxide.

Enthalpy change Energy change (kJ mol-1)
Atomisation of aluminium +326
Atomisation of oxygen +249
Second ionisation energy of aluminium +1817
Third ionisation energy of aluminium +2745
Formation of aluminium oxide -1670

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