2022 RSS Chem Prelims SectB

13 Riverside Secondary School 6092/02/4E/PRELIM/2022 [Turn over NAME: NO: CLASS: RIVERSIDE SECONDARY SCHOOL PRELIMINARY EXAMINATION 2022 SUBJECT : Chemistry CODE/PAPER : 6092/02 LEVEL/STREAM : 4 Express DURATION : 1 hour 45 minutes

14 Riverside Secondary School 6092/02/4E/PRELIM/2022 [Turn over Section B Answer all three questions in this section. The last question is in the form of an either/or and only one of the alternatives should be attempted. B8 The formation of a covalent bond involves the sharing of electrons between two atoms to form a balance between attractive and repulsive forces between the two atoms being bonded. In a hydrogen molecule, the hydrogen atoms share a valence electron each via covalent bonding. The bond energy is the amount of energy required to break one mole of bonds. The bond energy of a H — H bond is 432 kJ/mol. Figure 8.1 shows how the bond energy between two hydrogen atoms varies with the distance between their nuclei. Fig. 8.1 A positive energy value means that repulsive forces between atoms are dominant, while a negative energy value means that attractive forces between atoms are dominant. atoms too close; repulsive force between atoms ideal distance; attractive force is at a maximum atoms too far apart; attractive force is weak energy (kJ/mol) + 0 ‒ ‒432 74 distance between atoms (pm)

15 Riverside Secondary School 6092/02/4E/PRELIM/2022 [Turn over The bond length is the average distance between the nuclei of two bonded atoms in a molecule where the attractive force is greatest. For a hydrogen molecule, this distance is 74 picometres. Table 8.2 shows how the H—H bond compares with the number of bonds, average bond energy and bond length of some elements in Period 2. Table 8.2 type of bond number of bonds average bond energy (kJ/mol) bond length (pm) H – H 1 432 74 O – O 1 142 148 O = O 2 494 121 N – N 1 167 145 N = N 2 418 N ≡ N 3 942 110 F – F 1 155 142 (a) Describe how the bond energy of H—H changes with the distance between the two hydrogen atoms. …………………………………………………………………………………………….….………. …………………………………………………………………………………………….….………. …………………………………………………………………………………………….….………. …………………………………………………………………………………………….….………. …………………………………………………………………………………………….……..…[3] (b) In terms of the forces between the subatomic particles present in the hydrogen atoms, explain the trend of the bond energy as the distance between the hydrogen atoms increases from 74 pm. …………………………………………………………………………….……………….…………. ……………………………………………………………………………….…………….…………. …………………………………