Worksheet: Hess Cycles Using Bond Energies

In this worksheet, we will practice calculating reaction enthalpies by comparing the standard bond enthalpies of the reactants and the products.

Q1:

What is the approximate enthalpy change for the reaction shown?

H()+Br()2HBr()22ggg

Use the bond enthalpies from the table.

BondBrBrHBrHH
Bond Enthalpy (kJ/mol)190370436

Q2:

What is the approximate enthalpy change for the reaction shown? CH()+3O()2CO()+2HO()24222gggg Use the bond enthalpies from the table.

BondCHCCCOHOOO
Bond Enthalpy (kJ/mol)415611741464498

Q3:

What is the approximate enthalpy change for the reaction shown? CH()+I()CHI()+HI()423gggg Use the bond enthalpies from the table.

BondCHCIHIII
Bond Enthalpy (kJ/mol)415240295150

Q4:

When a molecule can form two different structures, the structure with the stronger bonds is usually the more stable form. Using the bond energy values listed in the table, identify the correct structure of the hydroxylamine molecule.

BondHNHONO
Bond Enthalpy (kJ/mol)390464200
  • A
    NOHHH
  • B
    NOHHH

Q5:

Given that the energy of a CHH3 bond is 104 kcal/mol and that of an HOH bond is 119 kcal/mol, what is the reaction enthalpy for the following reaction? HOCHHOCH++423

Q6:

The energies of selected bonds are shown in the table.

BondCHCClHClClCl
Bond Energy (kcal/mol)1048510358

The chlorination of methane is described by the equation shown. CH+ClCHCl+HCl423 Using the values in the table, calculate the energy change in this reaction per mole of methane reacted.

Q7:

Hydrogen fluoride gas is formed by the reaction of hydrogen with fluorine, as shown. H()+F()2HF()22ggg

The standard enthalpy change for this reaction is 535 kJ/mol. The molar bond energies of H2 and F2 are 436 kJ/mol and 159 kJ/mol respectively. Calculate the energy of one HF bond.

  • A1.38×10 J
  • B6.74×10 J
  • C8.06×10 J
  • D9.38×10 J
  • E1.43×10 J

Q8:

Gaseous sulfuric acid decomposes at high temperature to form sulfur dioxide, oxygen, and steam. The bonds in these molecules have different energies, as indicated in the diagram. All labeled bond energies are in units of kilojoules per mole.

Calculate the enthalpy change for this reaction per mole of oxygen gas produced.

Nagwa uses cookies to ensure you get the best experience on our website. Learn more about our Privacy Policy.