Questions: Select all that apply Which of the following statements correctly describe the procedure used to calculate ΔH° for a reaction using bond enthalpies? Select all that apply. ΔH° is obtained by adding together the absolute values of the bond energies for all bonds broken and formed. ΔHbonds formed is always endothermic. The sum ΔHbonds broken is given a positive value. ΔH for the reaction is given by ΣBE(reactants) - ΣBE(products)

Solution Steps

Bond enthalpy, or bond energy, is the energy required to break a bond in a molecule. To calculate the standard enthalpy change (\(\Delta H^{\circ}\)) for a reaction using bond enthalpies, we consider the energy required to break bonds in the reactants and the energy released when new bonds are formed in the products.

• Statement 1: "ΔH° is obtained by adding together the absolute values of the bond energies for all bonds broken and formed."

  • This statement is incorrect. The correct procedure involves subtracting the total bond energies of the products from the total bond energies of the reactants: \(\Delta H = \Sigma BE(\text{bonds broken}) - \Sigma BE(\text{bonds formed})\).

• Statement 2: "ΔH_{\text{bonds formed}} is always endothermic."

  • This statement is incorrect. The formation of bonds is an exothermic process, meaning it releases energy.

• Statement 3: "The sum ΔH_{\text{bonds broken}} is given a positive value."

  • This statement is correct. Breaking bonds requires energy, so the enthalpy change for bonds broken is positive.

• Statement 4: "ΔH for the reaction is given by \(\Sigma BE(\text{reactants}) - \Sigma BE(\text{products})\)."

  • This statement is correct. The enthalpy change for the reaction is calculated by subtracting the total bond energies of the products from the total bond energies of the reactants.

Final Answer