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Lesson: Energy Changes in Reactions

Worksheet • 18 Questions

Q1:

Polytetrafluoroethylene (PTFE), a polymer widely used in lubricants and nonstick coatings, is produced from tetrafluoroethene:

C F F C F F

Tetrafluoroethene is synthesized via two reaction steps. In the first step, chloroform ( C H C l ) 3 reacts with hydrogen fluoride gas to form chlorodifluoromethane ( C H C l F ) 2 . In the second step, chlorodifluoromethane is converted to tetrafluoroethene. Both reactions generate hydrogen chloride gas as the only other product. The energies of selected bonds are shown in the table.

Bond H F H C l C H C F C C l C C C C C H
Bond Energy (kJ/mol) 565 428 411 485 327 346 602 411

Calculate the total change in bond energy when one mole of chloroform is converted to chlorodifluoromethane.

Calculate the total change in bond energy when one mole of chloroform is converted to tetrafluoroethene.

Q2:

Acrylonitrile ( C H N ) 3 3 is used in the production of synthetic rubbers and other polymeric materials. The main method for synthesizing acrylonitrile is to react propene gas ( C H ) 3 6 with ammonia and oxygen at high temperature. The bonds in these molecules have different energies, as indicated in the diagram. All labeled bond energies are in units of kilojoules per mole.

+ 6 02 4 11 3 46 6 4 59 2 + 4 94 3 + 3 86 2 6 02 4 11 2 8 87 O H H C C C H H H H H H O O H N H H C C C H N H H

Calculate the total change in bond energy for this reaction per mole of acrylonitrile produced.

Q3:

Ozone is a pungent pale blue gas involved in many important reactions in the atmosphere. It is generated reversibly from oxygen gas and reacts with nitric oxide ( N O ) to produce nitrogen dioxide ( N O ) 2 and nitrogen trioxide ( N O ) 3 . The bonds in these molecules have different energies, some of which are shown in the diagram. All bond energies are in units of kilojoules per mole.

3 79 6 26 4 66 4 94 N O N O O N O O O O O

For the reaction the total change in bond energy per mole of ozone reacted is 2 0 2 kJ/mol.

Calculate the total change in bond energy when one mole of nitrogen trioxide is produced from ozone and nitrogen dioxide.

Calculate the total change in bond energy when one mole of ozone is produced from oxygen gas.

Q4:

Hydrogen gas for industrial processes is usually produced by the steam reforming of methane ( C H ) 4 . In this reversible process, methane reacts with steam to produce hydrogen and carbon monoxide ( C O ) . The energies of selected bonds are listed in the table.

Bond H H C H O H C O
Bond Energy (kJ/mol) 432 411 459 1 0 7 2

Give a balanced chemical equation for this reaction.

  • A C H + H O C O + 3 H 4 2 2
  • B 2 C H + 2 H O 2 C O + 5 H 4 2 2
  • C C H + H O C O + 2 H 4 2 2
  • D 3 C H + 3 H O 3 C O + 5 H 4 2 2
  • E 2 C H + 2 H O 2 C O + 3 H 4 2 2

Calculate the total change in bond energy for this reaction, per mole of hydrogen gas produced.

Q5:

Acetic anhydride, an industrially useful reactive compound, can be synthesized in a number of steps from methyl acetate and carbon monoxide.

+ C H H H C O O C C O H H H C H C H H O O C H H H C O

The reactions are performed in a solution containing catalytic salts. The average energies of selected bonds are listed in the table.

Bond C H C C C C C C C O C O C O
Bond Energy (kJ/mol) 411 346 602 835 358 799 1 0 7 2

Calculate the total change in bond energy for this process, per mole of acetic anhydride produced.

The calculated change in bond energy for this process is likely to differ from the measured enthalpy change. Which of the following factors does not contribute to this discrepancy?

  • AThe enthalpy change is affected by the presence of a catalyst.
  • BHeat losses cause the measured enthalpy change to be larger than the true value.
  • CThe enthalpy change is affected by interactions with the solvent.
  • DBond energies vary with the reaction temperature.
  • EBond energies are affected by the other bonds in a molecule.

Q6:

The water-gas shift reaction is a major source of hydrogen gas for industrial processes. In this reaction, carbon monoxide is reacted with steam to produce hydrogen and carbon dioxide:

The energies of selected bonds are listed in the table. Calculate the total change in bond energy for this reaction, per mole of hydrogen gas produced.

Bond H H C H O H C O C O C O
Bond Energy (kJ/mol) 432 411 459 358 799 1 0 7 2

Q7:

In the Andrussow oxidation, methane, ammonia, and oxygen react to produce hydrogen cyanide ( H C N ) and water. The energies of selected bonds are listed in the table.

Bond C H N H O H O O O O C N C N C N
Bond Energy (kJ/mol) 411 386 459 142 494 305 615 887

Give a balanced chemical equation for this reaction.

  • A 2 C H + 2 N H + 3 O 2 H C N + 6 H O 4 3 2 2
  • B 2 C H + 4 N H + 9 O 4 H C N + 1 8 H O 4 3 2 2
  • C C H + N H + 2 O H C N + 4 H O 4 3 2 2
  • D 4 C H + 2 N H + 7 O 2 H C N + 1 4 H O 4 3 2 2
  • E 2 C H + 2 N H + 5 O 2 H C N + 1 0 H O 4 3 2 2

Calculate the total change in bond energy for this reaction per mole of hydrogen cyanide produced.

Q8:

The complete combustion of heptene ( C H ) 7 1 4 produces water and carbon dioxide gases as the only products. Using the bond energies listed in the table, calculate the total change in bond energy for this reaction, per mole of heptene combusted.

Bond C H C C C C C O C O C O O H O O O O
Bond Energy (kJ/mol) 411 346 602 358 799 1 0 7 2 459 142 494

Q9:

The complete combustion of methane produces water and carbon dioxide gases as the only products. Using the bond energies listed in the table, calculate the total change in bond energy for this reaction, per mole of methane combusted. Note that it may not be necessary to use all of the energy values shown.

Bond C H C O C O C O O H O O O O
Bond Energy (kJ/mol) 411 358 799 1 0 7 2 459 142 494

Q10:

Atmospheric nitrogen dioxide ( N O ) 2 reacts with methanol ( C H O H ) 3 generated from organic pollutants. This reaction produces nitric acid ( H N O ) 3 and methyl nitrite, a highly oxidizing species. The bonds in these molecules have different energies, as illustrated in the diagram. All labeled bond energies are in units of kilojoules per mole.

2 05 4 66 4 23 5 00 3 77 4 11 4 37 3 45 3 98 1 77 6 07 O H C H H H N O O N O O O H O C N H H H O

Calculate the total change in bond energy for this reaction, per mole of nitric acid produced.

Q11:

Acetylene ( C H ) 2 4 can react with a wide variety of compounds to produce useful organic compounds containing carbon-carbon double bonds. The average energies of selected bonds are listed in the table.

Bond H H H C l H B r C C C C C C C C l C B r C H
Bond Energy (kJ/mol) 432 428 362 346 602 835 327 285 411

By calculating the total changes in bond energy per mole of acetylene reacted, place the following reactions in order from the most exothermic to the least.

+ + + 2 . 1 . 3 . C H C H C C H H Cl H H Cl C H C H C H H C H H H H C C H H C H C H H Br H Br
  • A2, 3, 1
  • B3, 2, 1
  • C1, 2, 3
  • D1, 3, 2
  • E2, 1, 3

Q12:

Dinitrogen tetroxide ( N O ) 2 4 is a reactive molecule used in chemical synthesis and used as a rocket propellant. Each molecule of dinitrogen tetroxide is formed reversibly by the reaction of two molecules of nitrogen dioxide ( N O ) 2 . The bonds in these molecules have different energies, as indicated in the diagram. All labeled bond energies are in units of kilojoules per mole.

1 67 4 66 2 4 38 N O N O O O O N O

Calculate the total change in bond energy for this reaction, per mole of dinitrogen tetroxide produced.

Q13:

Under UV light, hydrogen and chlorine gases react reversibly to form hydrogen chloride: Using the bond energies listed in the table, calculate the total change in bond energy for this reaction, per mole of hydrogen gas reacted.

Bond H H H C l C l C l
Bond Energy (kJ/mol) 432 428 240

Q14:

Nitric oxide ( N O ) is a colorless gas produced industrially by the reaction of ammonia ( N H ) 3 with oxygen at high temperature. Reaction with further oxygen may generate nitrogen dioxide ( N O ) 2 , a toxic brown gas that is a strong contributor to air pollution. The bonds in these molecules have different energies, as indicated in the diagram. All labeled bond energies are in units of kilojoules per mole.

4 94 4 59 3 86 6 26 4 66 N O N O O O H H N H H H O O

Calculate the total change in bond energy when one mole of nitric oxide is produced from ammonia and oxygen.

Calculate the total change in bond energy when one mole of nitrogen dioxide is produced from ammonia and oxygen.

Q15:

Phosgene ( C O C l ) 2 is a highly toxic gas with the structure shown.

C Cl Cl O

The reaction of phosgene with water generates carbon dioxide and hydrochloric acid as the only products. Using the bond energies listed in the table, calculate the total change in bond energy for this reaction, per mole of phosgene reacted.

Bond C H O H C l H C O C O C O C C l
Bond Energy (kJ/mol) 411 459 428 358 799 1 0 7 2 327

Q16:

Alkanes from the fractional distillation of crude oil can be converted to more reactive alkenes by catalytic cracking. In the cracking of pentane ( C H ) 5 1 2 , one alkene and one alkane are produced. The energies of selected bonds are listed in the table.

Bond C H C C C C C C
Bond Energy (kJ/mol) 411 346 602 835

Calculate the total change in bond energy for this reaction per mole of pentane reacted.

Q17:

The complete combustion of ethene ( C H ) 2 4 produces water and carbon dioxide gases as the only products. Using the bond energies listed in the table, calculate the total change in bond energy for this reaction, per mole of ethene combusted.

Bond C H C C C C C O C O C O O H O O O O
Bond Energy (kJ/mol) 411 346 602 358 799 1 0 7 2 459 142 494

Q18:

In the Haber process, nitrogen and hydrogen gases react reversibly to produce gaseous ammonia ( N H ) 3 . There are no other products. The energies of selected bonds are listed in the table.

Bond N N N N N N H H N H
Bond Energy (kJ/mol) 167 418 942 432 386

Give a balanced chemical equation for this reaction.

  • A N + 3 H 2 N H 2 2 3
  • B N + 6 H 4 N H 2 2 3
  • C 2 N + 3 H 4 N H 2 2 3
  • D 2 N + 4 H 3 N H 2 2 3
  • E N + 6 H 2 N H 2 2 3

Calculate the total change in bond energy for this reaction, per mole of ammonia produced.

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