Question 1: Define bond energy and explain its significance in chemical reactions.

Answer: Bond energy is the amount of energy required to break one mole of a specific type of bond in a gaseous molecule. It is significant because it helps predict whether a reaction will be exothermic or endothermic based on bond-breaking and forming processes.

Question 2: Briefly describe how nanotechnology can utilise exothermic and endothermic reactions.

Answer: Nanotechnology uses exothermic reactions to generate heat for applications like drug delivery or material synthesis, and endothermic reactions to absorb heat in processes such as energy storage or temperature control at the nanoscale.

Question 3: Fill in the blank: Bond energy calculations are essential for understanding the energy changes during chemical __________.

Answer: reactions

Question 1: Calculate the overall energy change when 1 mole of aluminium reacts with sulphur to form aluminium sulphide, given the following bond energies: Al–Al = 133 kJ/mol, S=S = 226 kJ/mol, Al–S = 204 kJ/mol. Show your working.

Answer: Energy change = (Bond energies of bonds broken) – (Bond energies of bonds formed) = [Al–Al + S=S] – [Al–S x 2] = (133 + 226) – (204 x 2) = 359 – 408 = -49 kJ/mol. The reaction is exothermic.

Question 2: A nanotech device relies on an endothermic reaction involving bond breaking. If 50 kJ of energy is required to break bonds in 1 mole of molecules, and 30 kJ is released when new bonds form, what is the overall energy change?

Answer: Overall energy change = Energy absorbed to break bonds – Energy released in forming bonds = 50 – 30 = 20 kJ. The process is endothermic.

Question 1: Describe a basic experimental approach to measure bond energies in nanoscale materials. Include key variables and safety precautions (theory only).

Answer: An experimental approach involves using spectroscopy methods like Raman or IR spectroscopy to identify bond vibrations in nanoscale materials. Variables include temperature, pressure, and sample purity. Safety precautions include handling chemicals with proper PPE, working in well-ventilated areas, and following waste disposal regulations.

Question 2: Identify at least two variables that could affect the accuracy of bond energy calculations in nanoscale systems and explain how.

Answer: Variables include temperature, which affects bond vibration energies, and sample purity, as impurities can alter bond strengths and lead to inaccurate measurements.

Question 1: A nanomaterial synthesis process releases 150 kJ of energy per mole of bonds formed. If the average bond energy of the bonds formed is 250 kJ/mol, estimate the number of bonds formed in this process.

Answer: Number of bonds = Total energy released / Bond energy per bond = 150 / 250 = 0.6 mol of bonds.

Question 2: Explain how understanding bond energies can help improve the efficiency of nanotechnological devices used for drug delivery.

Answer: Knowing bond energies allows scientists to optimise reactions for minimal energy input or maximum energy release, improving efficiency. Accurate bond energy data helps design nanostructures that respond predictably to stimuli, ensuring controlled drug release and reducing energy costs.