Question

3(a) In an equilibrium reaction of gases Q2 and R2 to form QR, the energy content of the reactants is 100 kJ and that of the activated complex is 210 kJ. (i) Draw an energy profile diagram for the reaction. (ii) Determine the: I. activation energy of the reaction; II. enthalpy change (Delta)H of the reaction. (iii) Write a balanced equation for the reaction. (iv) State whether the reaction is exothermic or endothermic. (v) Give a reason for the answer given in 3(a)(iv). (b) Consider the following table: Element E, F, G, H | Atomic number 7, 9, 12, 13. (i) Write the electron configuration for each of the elements. (ii) State: I. two elements that are metals; II. element(s) most likely to form ion with a charge of +3; III. the element(s) which belong(s) to group (VII) on the periodic table; IV. the formula of the compound formed between F and G. (c) Define the term Isotope. (d) Name the three building blocks of matter.

Accepted Answer

(a)(i) [Energy profile diagram: y-axis Energy(kJ), x-axis Reaction progress. Reactants (Q2+R2) drawn at 100kJ, rising to a peak (activated complex) at 210kJ, then descending to products (2QR) at a lower energy level than the activated complex, illustrating an exothermic reaction profile.]
(ii) I. Activation energy = 210kJ - 100kJ = 110kJ. II. Q2+R2 -> 2QR (the reaction), with the enthalpy change (Delta)H being negative, since the energy involved in bond formation is greater than that involved in bond breaking.
(iii) Q2(g) + R2(g) -> 2QR(g).
(iv) The reaction is exothermic.
(v) This is because the energy involved in bond formation is greater than the energy involved in bond breaking.
(b)(i) Electron configuration: 7E = 1s2 2s2 2p3; 9F = 1s2 2s2 2p5; 12G = 1s2 2s2 2p6 3s2; 13H = 1s2 2s2 2p6 3s2 3p1.
(ii) I. 12G and 13H are metals. II. The element that will most likely form an ion with a charge of +3 is 13H. III. The element that belongs to group (VII) on the periodic table is 9F. IV. The formula of the compound formed between F and G is GF2.
(c) Isotopy is the occurrence of atoms of the same element with the same atomic number but different mass numbers.
(d) The building blocks of matter are: atoms, molecules and ions.

WAEC Chemistry 2020 Theory — Question 3

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