Question

Write equations for the following processes, noting appropriate conditions: (a) electrolysis of water; (b) electrolysis of molten LiH; (c) \(\mathrm{CaH}_{2}\) reacting with water; (d) \(\mathrm{Mg}\) treated with dilute nitric acid; (e) combustion of \(\mathrm{H}_{2}\) (f) reaction of \(\mathrm{H}_{2}\) with \(\mathrm{CuO}\).

Short answer

Electrolysis of water produces H2 and O2, LiH yields Li and H2, CaH2 with water forms Ca(OH)2 and H2, Mg with HNO3 produces Mg(NO3)2 and H2, H2 combustion creates water, and H2 with CuO forms Cu and water.

Step-by-step solution

Electrolysis of Water

In the electrolysis of water, electricity is used to split water into hydrogen and oxygen gases. The equation for this process is: \[ 2\text{H}_2\text{O}_{(l)} \rightarrow 2\text{H}_2_{(g)} + \text{O}_2_{(g)} \] This reaction occurs under the influence of an electrical current.

Electrolysis of Molten LiH

When molten lithium hydride (LiH) undergoes electrolysis, it decomposes into lithium metal and hydrogen gas: \[ \text{LiH}_{(l)} \rightarrow \text{Li}_{(l)} + \text{H}_{2(g)} \] This process requires that the LiH be in a molten state to conduct electricity.

Reaction of CaH2 with Water

Calcium hydride reacts with water to produce calcium hydroxide and hydrogen gas. The chemical equation is: \[ \text{CaH}_2 + 2\text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 + 2\text{H}_2 \] This reaction occurs readily at room temperature.

Reaction of Mg with Dilute Nitric Acid

When magnesium reacts with dilute nitric acid, magnesium nitrate, water, and hydrogen gas are formed: \[ \text{Mg} + 2\text{HNO}_3 \rightarrow \text{Mg(NO}_3)_2 + \text{H}_2O + \text{H}_2 \] This is assuming the acid concentration is not sufficient to produce nitrogen oxides.

Combustion of Hydrogen

Hydrogen combusts in the presence of oxygen to form water vapor. The balanced equation is: \[ 2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O} \] This reaction requires a spark or flame to ignite.

Reaction of H2 with CuO

Hydrogen gas reacts with copper(II) oxide to produce copper metal and water: \[ \text{H}_2 + \text{CuO} \rightarrow \text{Cu} + \text{H}_2\text{O} \] This reaction is carried out with heating to allow the reduction of CuO by hydrogen.

Key concepts

Electrolysis

Electrolysis is a chemical process where an electric current is used to drive a non-spontaneous reaction. This is seen manifestly in the electrolysis of water, which splits water molecules into hydrogen and oxygen gases. The chemical equation \[ 2\text{H}_2\text{O}_{(l)} \rightarrow 2\text{H}_2_{(g)} + \text{O}_2_{(g)} \] shows the transformation of liquid water into its gaseous components under the influence of electricity. Similarly, electrolysis of molten lithium hydride \(\text{LiH}\) allows the decomposition into lithium metal and hydrogen gas via the equation: \[ \text{LiH}_{(l)} \rightarrow \text{Li}_{(l)} + \text{H}_{2(g)} \].

• This process is key in industries like metal refining and production of nonmetals.
• The molten state is necessary for ionic compounds like \(\text{LiH}\) to allow electrical conduction.

The process exemplifies the versatility of electrolysis in separating elements under controlled conditions.

Combustion Reaction

A combustion reaction is a type of chemical reaction where a substance reacts with oxygen, releasing energy in the form of light or heat. For example, the combustion of hydrogen involves hydrogen gas reacting with oxygen to form water, represented by the equation: \[ 2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O} \]. This exothermic reaction requires an initial input of energy, such as a spark, to initiate the process. Combustion is vital in various applications:

• Used as a fuel source due to the release of heat and energy.
• Involves complete combustion when sufficient oxygen is present, producing water and carbon dioxide.

Hydrogen as a clean fuel showcases how combustion reactions can be harnessed for energy without emitting harmful byproducts.

Reaction with Water

Reactions with water commonly involve a chemical transformation that results in the generation of new compounds. An example is the reaction of calcium hydride \(\text{CaH}_2\) with water, which produces calcium hydroxide \(\text{Ca(OH)}_2\) and hydrogen gas. This reaction can be depicted as: \[ \text{CaH}_2 + 2\text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 + 2\text{H}_2 \]. Such reactions are fascinating because:

• Hydrogen gas produced can have significant uses as an industrial gas.
• This reaction proceeds easily at room temperature, indicating it is thermodynamically favorable.

Reactions with water are crucial to understand, as they can impact chemical processes from simple lab experiments to large-scale industrial applications.

Redox Reaction

Redox reactions, short for reduction-oxidation reactions, involve the transfer of electrons between substances. A quintessential example is the reaction between hydrogen gas \(\text{H}_2\) and copper(II) oxide \(\text{CuO}\), which results in the production of copper metal and water. The equation for this reaction is: \[ \text{H}_2 + \text{CuO} \rightarrow \text{Cu} + \text{H}_2\text{O} \]. This reaction is significant because:

• Hydrogen serves as a reducing agent, donating electrons to \(\text{CuO}\), reducing it to \(\text{Cu}\).
• These reactions often require heating to proceed, facilitating the movement of electrons.

Redox reactions are foundational in fields like electrochemistry and are essential in energy transfer in biological systems.

Acid-Base Reaction

Acid-base reactions are fundamental chemical processes-driven by the transfer of protons. When magnesium \(\text{Mg}\) reacts with dilute nitric acid \(\text{HNO}_3\), a salt \(\text{Mg(NO}_3)_2\), water, and hydrogen gas are produced. The chemical equation is: \[ \text{Mg} + 2\text{HNO}_3 \rightarrow \text{Mg(NO}_3)_2 + \text{H}_2\text{O} + \text{H}_2 \]. These reactions highlight several important attributes:

• This showcases how metals react with acids to produce hydrogen gas.
• The formation of salts is common as acids neutralize bases.

Acid-base reactions form the core of many chemical interactions, from industrial processes to biological functions, demonstrating their widespread importance.