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

Chlorine is more reactive than iodine because it has fewer electron shells. This means that its outer electrons are located closer to the nucleus, which increases the nucleus's attractive force on incoming electrons. As a result, chlorine can gain an electron more easily compared to iodine, which has more electron shells, resulting in lower nuclear attraction for its outer electrons.

Hydrogen chloride is a gas at room temperature because it is composed of simple molecules. These molecules are held together by weak intermolecular forces, which require very little energy to overcome. Therefore, hydrogen chloride can exist as a gas easily at room temperature.

To calculate the bond energy X for the C—H bond, we can use the given overall energy change and bond energies.

1. Calculate the total energy for bonds broken and formed:

   • Bonds broken: 4(C—H) + 1(Br—Br) = 4(412) + 193 = 1841 kJ/mol
   • Bonds formed: 3(C—H) + 1(H—Br) + X = 3(412) + 366 + X = 1602 + X kJ/mol

2. Set up the equation based on the overall energy change: $-51 = 1841 - (1602 + X)$

3. Solving for X: $-51 + 1602 + X = 1841$ $X = 1841 - 1602 + 51$ $X = 290 ext{ kJ/mol}$

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