(a)(i) State three differences between electrovalent compound and covalent compound. (ii) Name the type of chemical bonding involved in the formation of amm...
Question 1 Report
(a)(i) State three differences between electrovalent compound and covalent compound.
(ii) Name the type of chemical bonding involved in the formation of ammonium ion from ammonia.
(b)(i) Name the quantum numbers which define an electron within an atom.
(ii) State the orbital in which the fifth electron of an atom is most likely to be found. Sketch the shape of the orbital.
(iii) State the period and the group to which the element boron belongs in the Periodic Table.
(c)(i) What is meant by the entropy of a chemical system?
(ii) Calculate the free energy change for a given reaction at 300 K using the following data obtained for the reaction: \(\Delta\) = -710KJ mol\(^{-1}\); \(\Delta\)S = 0.15 KJ mol\(^{-1}\)K\(^{-1}\)
(iii) From your evaluation in (c)(i) above, state whether the reaction is spontaneous or not at the given temperature. Give reason for your answer.
Answer Details
(a)(i) Differences between electrovalent and covalent compounds
| Electrovalent (ionic) compounds | Covalent compounds |
|---|---|
| They consist of oppositely charged ions held by strong electrostatic forces. | They consist of discrete molecules formed by sharing electrons. |
| They conduct electricity when molten or when dissolved in water because their ions are mobile. | They generally do not conduct electricity because they contain no mobile ions. |
| They usually have high melting and boiling points and are commonly soluble in water. | They usually have relatively low melting and boiling points and are commonly soluble in organic solvents. |
(a)(ii) The bond formed when ammonia accepts a hydrogen ion to form ammonium ion is a coordinate (dative covalent) bond.
\[\mathrm{NH_3 + H^+ \longrightarrow NH_4^+}\]
The nitrogen atom donates its lone pair of electrons to \(\mathrm{H^+}\).
(b)(i) The four quantum numbers are:
- principal quantum number, \(n\);
- azimuthal or angular momentum quantum number, \(l\);
- magnetic quantum number, \(m_l\);
- spin quantum number, \(m_s\).
(b)(ii) The electronic arrangement of an atom with five electrons is \(1s^2\,2s^2\,2p^1\). Therefore, the fifth electron is in a 2p orbital. A 2p orbital is dumb-bell shaped.
(b)(iii) Boron, \(1s^2\,2s^2\,2p^1\), is in Period 2 and Group 13 (Group IIIA) of the Periodic Table.
(c)(i) Entropy is a measure of the degree of disorderliness or randomness of a chemical system.
(c)(ii)
\[\Delta G=\Delta H-T\Delta S\]
\[\Delta G=-710-\left(300\times0.15\right)\]
\[\Delta G=-710-45=-755\ \text{kJ mol}^{-1}\]
(c)(iii) The reaction is spontaneous at \(300\,\text{K}\), because \(\Delta G\) is negative.
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