Question 1: Bond energy is the amount of energy required to break one mole of a specific type of bond in a gaseous molecule. It is measured in kilojoules per mole (kJ/mol). When bonds are formed, energy is released, making the process exothermic. Conversely, breaking bonds absorbs energy, making the process endothermic.

Answer: Bond energy is the energy needed to break a bond in a molecule; bond formation releases energy, bond breaking absorbs energy.

Question 1: Define an exothermic reaction.

Answer: An exothermic reaction releases energy to the surroundings, usually in the form of heat.

Question 2: Explain why breaking bonds requires energy while forming bonds releases energy.

Answer: Breaking bonds requires energy because it involves overcoming the attractive forces between atoms. Forming bonds releases energy as atoms come together and establish stable attractive forces, resulting in a net energy change.

Question 1: Calculate the overall energy change for the reaction: H₂ + Cl₂ → 2HCl, given the following bond energies: H–H = 432 kJ/mol, Cl–Cl = 243 kJ/mol, H–Cl = 431 kJ/mol.

Answer: ΔH = (Bond energies of bonds broken) – (Bond energies of bonds formed) = [(H–H) + (Cl–Cl)] – [2 × (H–Cl)] = (432 + 243) – (862) = 675 – 862 = -187 kJ/mol

Question 2: Determine whether the reaction in question 4 is exothermic or endothermic based on your calculation.

Answer: The reaction is exothermic because the overall energy change is negative, indicating energy is released.

Question 1: Describe a simple experimental setup to measure bond energies using a calorimeter. Include variables to control and safety precautions.

Answer: A calorimeter can be used by placing reactants in a sealed container to measure temperature change during a reaction. Variables to control include mass of reactants, initial temperature, and pressure. Safety precautions involve wearing protective gloves and goggles, handling chemicals carefully, and ensuring proper ventilation.

Question 1: A reaction releases 1500 kJ of energy when 3 moles of bonds are broken and formed. What is the average bond energy per bond involved? Assume an equal number of bonds are broken and formed.

Answer: Average bond energy per bond = Total energy released / Number of bonds involved = 1500 kJ / 3 = 500 kJ/mol

Question 2: Explain how industries might use bond energy calculations to develop more efficient fuels or explosives.

Answer: Industries analyse bond energies to identify reactions that release maximum energy with minimal input. For fuels, choosing molecules with bonds that release more energy upon breaking improves efficiency. For explosives, understanding bond energies helps in designing compounds that decompose rapidly and release large amounts of energy safely and reliably.