I've been given a table with the following information:
Br-Br bonding energy (298 K): 192.807 kJ/mol
Br2 vaporization energy: 30.91 kJ/mol
boiling point of bromine: 332 K
The question reads, "A chemist heats liquid bromine to 335K, and a gas forms. Is the change that occurs a physical change, a chemical change, or both? Support your answer using the data and a discussion of intramolecular and intermolecular forces."
I want to say that this is a physical change because the chemist heated the bromine past its boiling point, so doesn't that mean it was vaporized? The bond energy is so much higher than that vaporization energy that I don't see how the heating would have added enough energy to break the covalent bonds, except for the little 298 K they put by the bond energy. Would that, then, indicate that bonds were broken and this is thus a chemical change? Is it even possible for it to be both?
Thanks for any assistance!
To determine whether the change is a physical change, a chemical change, or both, we need to examine the data and consider the concepts of intramolecular and intermolecular forces.
Intramolecular forces refer to the bonds that hold atoms together within a molecule, while intermolecular forces are the forces of attraction between different molecules.
Looking at the given data, the boiling point of bromine is 332 K. This is the temperature at which the intermolecular forces holding the liquid bromine together are overcome, and the substance changes from a liquid to a gas (vaporization).
The question states that the chemist heated the liquid bromine to 335 K, slightly above its boiling point.
Based on this information, we can infer that the change that occurs is the vaporization of bromine, which is a physical change. By heating the bromine above its boiling point, the intermolecular forces holding the liquid bromine together are broken, and it is converted into a gas.
It is important to note that the high bond energy of Br-Br, which is the energy required to break the covalent bonds within a bromine molecule, indicates that it would require much more energy to break these bonds compared to the energy required for vaporization. This suggests that under normal conditions, heating alone would not be sufficient to break the covalent bonds, supporting the notion that the change is primarily a physical change.
In conclusion, based on the given data and the discussion of intramolecular and intermolecular forces, the change that occurs when the chemist heats liquid bromine to 335 K is a physical change.