Bond Enthalpies

Use your bond enthalpy sheet and a piece of paper to do the calculations.

What is the enthalpy change for the decomposition of hydrogen chloride?

2 HCl --> H₂ + Cl₂

• -184 kJ

• + 184 kJ

• - 247 kJ

• + 247 kJ

Calculate the enthalpy change for the reaction shown.

• -102kJ

• +102kJ

• +146kJ

• -248 kJ

Calculate the enthalpy change, in kJ/mol for the reaction

H_{2 (g)} + ½O_{2 (g)} → H₂O _(g)

Use your bond enthalpy sheet and a piece of paper to do the calculation.

• −243 kJ/mol

• −6 kJ/mol

• +6 kJ/mol

• +221 kJ/mol

The enthalpy change for the reaction between hydrochloric acid and sodium hydroxide is −56 kJ/mol. Therefore ...

• the reaction is exothermic and the temperature rises

• the reaction is exothermic and the temperature falls

• the reaction is endothermic and the temperature rises

• the reaction is endothermic and the temperature falls

Which of these diagram correctly represent an endothermic reaction?

• 
• 
• 
• 

Example of endothermic reaction is ...

• Combustion

• Photosynthesis

• Neutralization

• Respiration

What happens when chemical bonds are broken?

• Energy is released

• An explosion occurs

• An exothermic process take place

• An endothermic process take place

Which statements about exothermic reactions are correct?

I. They have negative ΔH values

II. The products have a lower energy than the reactants III. The products are more energetically stable than the reactants

• I and II only

• I and III only

• II and III only

• I, II, and III

The average bond enthalpies for O-O and O=O are 146 and 496 kJ/mol respectively. What is the enthalpy change, in kJ, for the reaction below?

H-O-O-H(g) → H-O-H(g) + ½O=O(g)

Use paper for your calculations.

• -102

• +102

• +350

• +394

When the solids Ba(OH)₂ and NH₄SCN are mixed, a solution is produced and the temperature drops. Which statement about the energetics of this reaction is correct?

• The reaction is endothermic and ΔH is negative

• The reaction is endothermic and ΔH is positive

• The reaction is exothermic and ΔH is negative

• The reaction is exothermic and ΔH is positive