This question is about Group 7 elements - AQA - GCSE Chemistry - Question 7 - 2018 - Paper 1

Chlorine is more reactive than iodine due to several factors:

1. Electron Shell Structure: Chlorine has fewer electron shells than iodine, which means its outer electrons are located closer to the nucleus. This proximity allows the nucleus to exert a stronger attractive force on the outer electrons.

2. Effective Nuclear Charge: Chlorine's nucleus has a greater effective nuclear charge due to its higher atomic number. This charge helps chlorine to gain an electron more easily compared to iodine, which has more electron shielding from its additional shells.

3. Electron Affinity: Chlorine can attract electrons more readily because it has a higher electron affinity than iodine, making it more favorable for chlorine to participate in reactions.

Hydrogen chloride is a gas at room temperature because it is composed of simple molecular structures. These molecules are held together by weak intermolecular forces, which require relatively little energy to overcome. As a result, at room temperature, the energy provided is sufficient for these bonds to break, allowing hydrogen chloride to remain in its gaseous state.

To calculate the bond energy X for the C–H bond, we use the formula for overall energy change in the reaction:

1. Calculate the total energy of the bonds broken:

   • Bonds broken: 4(C–H) + 1(Br–Br) = 4(412) + 193 = 1841 kJ/mol

2. Next, calculate the total energy of the bonds formed:

   • Bonds formed: 3(C–H) + 1(C–Br) + 1(H–Br) + X = 3(412) + 366 + X = 1602 + X

3. The overall energy change is given as -51 kJ/mol, thus we can set up the equation: $-51 = 1841 - (1602 + X)$

4. Rearranging this gives: $X = 1841 - 1602 + 51 = 290 ext{ kJ/mol}$

Therefore, the bond energy X for the C–H bond is 290 kJ/mol.