Using the activity series (Table 4.5), write balanced chemical equations for the following reactions. If no reaction occurs, write \(\mathrm{NR}\) . (a) Nickel metal is added to a solution of copper(II) nitrate, (b) a solution of zinc nitrate is added to a solution of magnesium sulfate, (c) hydrochloric acid is added to gold metal, (d) chromium metal is immersed in an aqueous solution of cobalt(II) chloride, (e) hydrogen gas is bubbled through a solution of silver nitrate.

Chemical reactivity is a property that describes how readily a substance undergoes a chemical change. This property is determined by a variety of factors including the arrangement of electrons within atoms and the structure of the elements involved. In the context of the activity series, chemical reactivity refers to a metal’s ability to displace another metal from a compound. For example, in the exercise, Nickel is able to displace Copper from copper(II) nitrate due to its higher reactivity.

Understanding reactivity trends among metals, such as those shown in an activity series table, is crucial for predicting the outcomes of chemical reactions. The activity series is a chart of metals listed in order of decreasing reactivity. Highly reactive metals, such as alkali metals, are placed at the top, indicating that they can replace other metals beneath them in compounds, while less reactive metals are found towards the bottom.

Balancing chemical equations is a fundamental skill in chemistry that involves making sure the number of atoms for each element is the same on both sides of the equation. This conservation of mass ensures that the reaction is physically possible. In the provided exercise solutions, balancing entails adding coefficients to the reactants and products to achieve this balance.

For example, in reaction (e), the reaction between hydrogen gas and silver nitrate is balanced by placing a coefficient of 2 in front of the reactants and products to ensure 2 atoms of hydrogen and 2 silver atoms are present on each side of the equation. A balanced chemical equation is essential for quantitatively describing the stoichiometry of a reaction, which is the relationship between the quantities of reactants and products.

Redox reactions, short for reduction-oxidation reactions, involve the transfer of electrons between substances. In these reactions, one substance is oxidized (loses electrons) while another is reduced (gains electrons). The activity series helps predict which metal will be oxidized and which will be reduced in a metal displacement reaction.

Oxidation states of the elements involved in the reactions change. For instance, in the case of Nickel displacing Copper, Nickel undergoes oxidation by losing electrons to form Ni²⁺, while Copper is reduced upon gaining these electrons. The concept of redox is highlighted in these reactions where a more reactive metal, such as Nickel or Chromium, will tend to lose electrons and be oxidized compared to a less reactive metal.

The reactivity of metals significantly influences the course of a chemical reaction. Metals with high reactivity readily lose electrons and form positive ions or cations, making them more likely to participate in chemical reactions, such as those involving metal displacement. In our exercise, the activity series serves as the guide to recognize the relative reactivity of metals.

A key application of understanding metal reactivity is in predicting product formation in reactions, like in part (d) of the exercise, where Chromium, being more reactive, displaces Cobalt from cobalt(II) chloride, resulting in the formation of Chromium chloride. These reactions are critical in various industrial processes, such as the extraction of metals and the manufacturing of electronic components.