(a) In an equilibrium reaction between gases Q and R, to form QR, the energy content of the reactants is 100 KJ and that of the product is 54 kJ. The energy content 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 il. enthalpy change ΔH of the reaction. (iii) Write a balanced equation for the reaction. (iv) Give a reason for the answer given in 3(C)(iv). (iv) State whether the reaction is exothermic or endothermic.
(i) Write the electron configuration for each of the elements. Element E, F, G, H 12 13 (ii) State: I. two elements that are metals; II. the elements(s) most likely to form an 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. Atomic
(c) Define the term isotopy (d) Name the three building blocks of matter.
(a) Energy of reactants \(= 100\,\text{kJ}\); energy of product \(= 54\,\text{kJ}\); energy of activated complex \(= 210\,\text{kJ}\).
(i) Energy profile diagram. On axes of energy (vertical) against reaction pathway (horizontal), mark the reactants \((Q + R)\) at \(100\,\text{kJ}\). Draw the curve rising to a peak, the activated complex, at \(210\,\text{kJ}\), then falling to the product \((QR)\) at \(54\,\text{kJ}\). Label the rise from reactants to the peak as the activation energy \((E_a)\) and the fall from the reactant level to the product level as the enthalpy change \((\Delta H)\).
| Stage | Energy / kJ |
|---|
| Reactants \((Q + R)\) | 100 |
| Activated complex (peak) | 210 |
| Product \((QR)\) | 54 |
(ii) I. Activation energy \(= E_{\text{complex}} - E_{\text{reactants}} = 210 - 100 = 110\,\text{kJ}\).
II. Enthalpy change \(\Delta H = H_{\text{product}} - H_{\text{reactant}} = 54 - 100 = -46\,\text{kJ}\).
(iii) \[ Q_2 + R_2 \rightleftharpoons 2QR \]
(iv) The reaction is exothermic.
(v) It is exothermic because \(\Delta H\) is negative: the energy of the product is lower than that of the reactants, so energy is given out to the surroundings.
(b) Elements E (7), F (9), G (12), H (13).
(i) Electron configurations
| Element | Atomic number | Configuration |
|---|
| E | 7 | \(1s^2\,2s^2\,2p^3\) |
| F | 9 | \(1s^2\,2s^2\,2p^5\) |
| G | 12 | \(1s^2\,2s^2\,2p^6\,3s^2\) |
| H | 13 | \(1s^2\,2s^2\,2p^6\,3s^2\,3p^1\) |
(ii) I. The two metals are G and H.
II. The element most likely to form an ion of charge \(+3\) is H \((H^{3+})\).
III. The element belonging to Group VII is F.
IV. F forms \(F^-\) and G forms \(G^{2+}\), so the compound is \(GF_2\).
(c) Isotopy is the phenomenon whereby atoms of the same element (same atomic number) exist in different forms having the same chemical properties but different atomic masses, because they contain different numbers of neutrons.
(d) The three building blocks of matter are atoms, ions and molecules.
