Energy And Energy Changes

(a) i. According to the Lewis concept, an acid is defined as a substance that can accept a pair of electrons (an electron pair acceptor) during a chemical reaction. In other words, acids are substances that can form coordinate covalent bonds by accepting electron pairs from other molecules or ions. ii. An example of a Lewis acid is boron trifluoride (BF3). BF3 has an incomplete octet and can accept an electron pair from a Lewis base to form a coordinate covalent bond. (b) Salting out in soap preparation refers to the process of adding salt (such as sodium chloride) to a soap mixture to separate the soap from the aqueous solution. When salt is added, it reduces the solubility of soap in water, causing the soap to precipitate or separate out. This occurs because the salt ions compete with the soap molecules for the water molecules, disrupting the soap-water interactions and promoting the formation of soap aggregates or micelles. (c) The reagent and condition necessary for the conversion of H-C≡C-H to Ag-C≡C-Ag is silver nitrate (AgNO3) and ammonia (NH3) as a complexing agent. The reaction takes place in the presence of sunlight or UV light. (d) The percentage abundance of an isotope refers to the relative abundance or proportion of a specific isotope in a naturally occurring sample of an element. It is expressed as a percentage and represents the fraction of the total number of atoms of the element that is composed of the specific isotope. (e) i. The element with atomic number 18 is argon (Ar), which belongs to the noble gas group. Noble gases are known for their stable electronic configurations and inert nature. Since argon already has a complete octet in its outer electron shell, it does not readily form compounds, including oxides. ii. Chlorine(I) oxide (Cl2O) has a low melting point due to its weak intermolecular forces. It exists as discrete Cl2O molecules held together by relatively weak van der Waals forces. These forces are easily overcome, resulting in a low melting point for the compound. (f) A test to distinguish between concentrated HNO3 (nitric acid) and concentrated H2SO4 (sulfuric acid) is to add a small piece of copper metal to each acid. Nitric acid is a strong oxidizing agent and will react with the copper, producing brown nitrogen dioxide gas (NO2) and dissolving the copper. Sulfuric acid, on the other hand, is not a strong oxidizing agent and will not react with copper under normal conditions. (g) Two differences between an electrochemical cell and an electrolytic cell are: 1. In an electrochemical cell (such as a voltaic cell or a galvanic cell), the chemical reactions are spontaneous and produce electrical energy. In contrast, an electrolytic cell requires an external source of electrical energy to drive non-spontaneous reactions. 2. In an electrochemical cell, electrons flow spontaneously from the anode (where oxidation occurs) to the cathode (where reduction occurs). In an electrolytic cell, the direction of electron flow is reversed by the external power source to drive the non-spontaneous reactions. (h) The trend in ionization energy, which refers to the energy required to remove an electron from an atom or ion, affects the reactivity of group 1 elements (alkali metals). As we move down the group from top to bottom, the ionization energy decreases. This means that the outermost electron in alkali metals is increasingly farther from the nucleus and more loosely held. As a result, the reactivity of alkali metals increases down the group because it becomes easier for