# Worksheet: Hess Cycles Using Standard Entropies

Q1:

The standard entropies of nitric oxide and other materials are shown below:

 Material Standard Molar Entropy π β¦΅ 2 9 8 ( J / K Β· m o l ) N O ( ) 2 g N O ( ) g N O ( ) 2 g O ( ) g O ( ) 2 g N ( ) g N ( ) 2 g 240.1 210.8 220.0 161.1 205.2 153.3 191.6

Calculate, to 1 decimal place, the standard entropy change, , for the formation of nitric oxide from the constituent elements in their standard states, expressed per mole of nitric oxide produced.

Q2:

The standard molar entropy changes for four reactions are given below:

 Reaction Standard Molar Entropy Change Ξ π β¦΅ 2 9 8 (J/Kβ mol) 2 H O ( ) + O ( ) 2 H O ( ) 2 2 2 2 g g g 2 H ( ) + O ( ) 2 H O ( ) 2 2 2 g g g H ( ) 2 H ( ) 2 g g O ( ) 2 O ( ) 2 g g β 3 6 3 . 6 β 8 9 . 0 98.7 117.0

Calculate, to 3 significant figures, for the reaction .

Q3:

The standard entropies of methanol and other materials are shown in the table:

 Material Standard Molar Entropy, π β¦΅ 2 9 8 ( J / K Β· m o l ) C H O H ( ) 3 l C H O H ( ) 3 g O ( ) g O ( ) 2 g C ( π π π π β π π‘ π ) C O ( ) g C O ( ) 2 g H O ( ) 2 g 126.8 239.9 161.1 205.2 5.7 197.7 213.8 188.8

Calculate the standard entropy change, , for the complete combustion of methanol in the gas phase, expressed per mole of methanol reacted.

Q4:

The standard entropies of calcium hydroxide and other materials are shown in the table:

 Material Standard Molar Entropy, π β¦΅ 2 9 8 ( J / K Β· m o l ) C a ( O H ) ( ) 2 s C a ( ) s C a O ( ) s O ( ) 2 g H O ( ) 2 g H ( ) 2 g 83.4 41.6 38.1 205.2 188.8 130.7

Calculate the standard entropy change, , for the conversion of solid calcium hydroxide to solid calcium oxide and gaseous by-products, expressed per mole of reactant.

Q5:

In the Haber-Bosch process, gaseous ammonia is produced from nitrogen and hydrogen gases. The standard entropies of these and other materials are shown below:

 Material Standard Molar Entropy π β¦΅ 2 9 8 (J/Kβ mol) H ( ) 2 g H ( ) + a q H ( ) g N ( ) 2 g N ( ) g N H ( ) 3 g N H ( ) 2 4 g 130.7 0.0 114.7 191.6 153.3 192.8 238.5

Calculate, to 3 significant figures, the standard entropy change for this reaction, expressed per mole of nitrogen reacted.

Calculate, to 3 significant figures, the maximum value of , the standard enthalpy change per mole of nitrogen, at which this reaction would occur spontaneously at 298 K.

Q6:

Lead reacts with hydrogen chloride gas to form lead(II) chloride and hydrogen. The standard entropies of these and other materials are shown in the table.

 Material Standard Molar Entropy π β¦΅ 2 9 8 (J/Kβ mol) P b ( ) s P b ( ) g P b C l ( ) 2 s H C l ( ) g H ( ) g H ( ) 2 g 64.8 175.4 136.0 186.9 114.7 130.7

Calculate, to 3 significant figures, the standard entropy change for this reaction, , expressed per mole of lead consumed.

Calculate, to 3 significant figures, the maximum value of , the standard molar enthalpy change per mole of lead, at which this reaction would occur spontaneously at 298 K.

Q7:

Ethane gas can be produced by the hydrogenation of gaseous ethene. The standard molar entropy, , for ethane is 229.2 J/Kβmol, the value for ethene is 219.3 J/Kβmol, and the value for hydrogen is 130.7 J/Kβmol.

Give a balanced chemical equation for this process including state symbols.

• A
• B
• C
• D
• E

Calculate the standard molar entropy change for this process, .

Q8:

The complete combustion of propane produces carbon dioxide and steam. The standard entropies of these and other materials are shown in the table.

 Material Standard Molar Entropy π β¦΅ 2 9 8 (J/Kβ mol) C H O H ( ) 2 5 g C H ( ) 3 8 g C O ( ) g C O ( ) 2 g O ( ) 2 g O ( ) g H O ( ) 2 l H O ( ) 2 g 281.6 270.3 197.7 213.8 205.2 161.1 70.0 188.8

Calculate, to 3 significant figures, the standard entropy change for this reaction, , expressed per mole of propane combusted.

Q9:

The standard entropies of copper(I) sulfide and other materials are shown in the table.

 Material Standard Molar Entropy π β¦΅ 2 9 8 (J/Kβ mol) C u S ( ) s C u S ( ) 2 s C u ( ) g C u ( ) s S ( ) 8 s S ( ) g 66.5 120.9 166.4 33.2 256.8 167.8

Calculate the standard entropy change for the formation of copper(I) sulfide from the constituent elements in their standard states, expressed per mole of copper(I) sulfide produced.

Q10:

The standard entropies of water and other materials are shown in the table.

 Material Standard Molar Entropy π β¦΅ 2 9 8 (J/Kβ mol) H O ( ) 2 g H O ( ) 2 l H O ( ) 2 2 l H ( ) 2 g H ( ) g O ( ) 2 g O ( ) g 188.8 70.0 109.6 130.7 114.7 205.2 161.1

Calculate, to 3 significant figures, the standard entropy change for the formation of liquid water from its constituent elements in their standard states, expressed per mole of water.

Calculate, to 3 significant figures, the maximum value of , the standard molar enthalpy change per mole of water, at which this reaction would occur spontaneously at 298 K.

Q11:

The standard entropies of graphite and other materials are shown below:

 Material Standard Molar Entropy π β¦΅ 2 9 8 ( J / K Β· m o l ) C ( ) d i a m o n d C ( ) g r a p h i t e C ( ) g O ( ) g O ( ) 2 g C O ( ) g C O ( ) 2 g 2.4 5.7 158.1 161.1 205.2 197.7 213.8

Calculate, to 1 decimal place, the standard entropy change, , for the complete combustion of graphite, expressed per mole of carbon dioxide produced.

Q12:

Dinitrogen pentoxide can be produced from nitrogen and oxygen gases. The standard entropies of these and other materials are shown in the given table.

 Material Standard Molar Entropy π β¦΅ 2 9 8 (J/Kβ mol) O ( ) 2 g O ( ) g O ( ) 3 g N ( ) 2 g N ( ) g N O ( ) 2 3 g N O ( ) 2 4 g N O ( ) 2 5 g 205.2 161.1 238.9 191.6 153.3 312.2 304.4 355.7

Calculate, to 3 significant figures, the standard entropy change for this reaction, expressed per mole of nitrogen reacted.

Calculate, to 3 significant figures, the maximum value of , the standard enthalpy change per mole of nitrogen, at which this reaction would occur spontaneously at 298 K.

Q13:

The standard entropies of iron(III) oxide and other materials are shown in the table.

 Material Standard Molar Entropy π β¦΅ 2 9 8 (J/Kβ mol) F e O ( ) s F e O ( ) 2 3 s F e O ( ) 3 4 s F e ( ) s C ( π π π π β π π‘ π ) C O ( ) g C O ( ) 2 g 60.8 87.4 146.4 27.3 5.7 197.7 213.8

Calculate the standard entropy change for the reduction of iron(III) oxide to iron by carbon monoxide, expressed per mole of iron(III) oxide reacted.

Q14:

The standard entropies for a range of fuels and their decomposition products are shown in the table.

 Material Standard Molar Entropy π β¦΅ 2 9 8 (J/Kβ mol) N H ( ) 3 g B H ( ) 2 6 g N H ( ) 2 4 l N H ( ) 2 4 g H O ( ) 2 2 l H O ( ) 2 2 g K C l O ( ) 3 s N ( ) 2 g H ( ) 2 g O ( ) 2 g B ( ) g H O ( ) 2 g K C l ( ) s 192.8 232.1 121.2 238.5 109.6 232.7 143.0 191.6 130.7 205.2 153.4 188.8 83.0

Which of the following reactions produces the smallest increase in entropy per mole of reactant under standard conditions?

• A
• B
• C
• D
• E

Q15:

In the thermite reaction, solid iron(III) oxide reacts with aluminum to produce aluminum oxide and iron. The standard entropies of these and other materials are shown in the following table:

 Material Standard Molar Entropy π β¦΅ 2 9 8 (J/Kβ mol) F e ( ) s F e ( ) g F e O ( ) 3 4 s F e O ( ) s F e O ( ) 2 3 s A l ( ) s A l ( ) g A l O ( ) 2 3 s 27.3 180.5 197.7 213.8 205.2 28.3 164.5 50.9

Calculate, to 3 significant figures, the standard entropy change for this reaction, expressed per mole of iron(III) oxide reacted.

Calculate, to 3 significant figures, the maximum value of , the standard enthalpy change per mole of iron(III) oxide, at which this reaction would occur spontaneously at 298 K.