A3.2 - Hexane and Bromine Hexane and Bromine are mixed together in three tubes and each tube is then exposed to a different light level.

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A3.2 - Hexane and Bromine Hexane and Bromine are mixed together in three tubes and each tube is then exposed to a different light level.

Sides covered with foil Tube completely covered with foil Uncovered

Hexane and Bromine Start At different times the foil is removed and a photograph is taken 10mins 20mins 30mins

Now watch a video clip to see what happens when a glass rod is used to dispense ammonia gas to tubes 1 and 3. Click on photo to start.

Questions What evidence is there that bromine undergoes photodissociation? Look up the values for Br-Br and C-H bond enthalpies. Remember that bond enthalpies are given per mole of bonds. Calculate the enthalpy change when (i) one Br-Br bond is broken, (ii) one C-H bond is broken. Use E=hv and calculate the frequencies of photons of radiation corresponding to each of these energies. Which bond is most likely to be broken by absorption of sunlight? What has the bromine reacted with? What is the gaseous product that is formed? Write an equation, with state symbols, for the reaction of this gas with ammonia.