Question

Write chemical equations for the reactions you would expect to occur when (a) \(\operatorname{Mg}\left(\mathrm{HCO}_{3}\right)_{2}(\mathrm{s})\) is heated to a high temperature (b) \(\mathrm{BaCl}_{2}(1)\) is electrolyzed (c) \(\operatorname{Sr}(\text { s) is added to cold dilute } \operatorname{HBr}( \text { aq) }\) (d) \(\mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{aq})\) is added to \(\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq})\) (e) \(\mathrm{CaSO}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O}(\mathrm{s})\) is heated

Short answer

The exercise involves writing equations for several types of chemical reactions: (a) thermal decomposition, (b) electrolysis, (c) displacement, (d) neutralization and (e) dehydration.

Step-by-step solution

(a) Heating \(\operatorname{Mg}\left(\mathrm{HCO}_{3}\right)_{2}(\mathrm{s})\)

When \(\operatorname{Mg}\left(\mathrm{HCO}_{3}\right)_{2}(\mathrm{s})\) is heated, it decomposes into magnesium oxide (MgO), water (H2O), and carbon dioxide (CO2). It is a type of thermal decomposition reaction. The equation is:\[\operatorname{Mg}\left(\mathrm{HCO}_{3}\right)_{2}(\mathrm{s})\rightarrow \operatorname{MgO}\left(\mathrm{s}\right)+\mathrm{H}_{2}\mathrm{O}(\mathrm{g})+2 \mathrm{CO}_{2}(\mathrm{g})\]

(b) Electrolysis of \(\mathrm{BaCl}_{2}(l)\)

Electrolysis involves breaking down a compound into its elements using an electric current. \(\mathrm{BaCl}_{2}\) will break down into barium (Ba) and chlorine (Cl2) gas. The equation is:\[\mathrm{BaCl}_{2}(l) \rightarrow \mathrm{Ba}(s)+\mathrm{Cl}_{2}(g)\]

(c) Adding $\operatorname{Sr}\left(\mathrm{s}\right)$ to cold dilute $\operatorname{HBr}\left(\mathrm{aq}\right)$

When strontium (Sr) is added to cold dilute hydrobromic acid (HBr), a displacement reaction occurs, creating strontium bromide (SrBr2) and hydrogen gas (H2). The equation is:\[\mathrm{Sr}\left(\mathrm{s}\right)+2 \mathrm{HBr}\left(\mathrm{aq}\right) \rightarrow \mathrm{SrBr}_{2}\left(\mathrm{aq}\right)+\mathrm{H}_{2}\left(\mathrm{g}\right)\]

(d) Adding \(\mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{aq})\) to \(\mathrm{H}_{2}\mathrm{SO}_{4}(\mathrm{aq})\)

A neutralization reaction takes place when calcium hydroxide (Ca(OH)2) is added to sulphuric acid (H2SO4), forming calcium sulphate (CaSO4) and water (H2O). The equation is:\[\mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq}) \rightarrow \mathrm{CaSO}_{4}(\mathrm{aq})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})\]

(e) Heating \(\mathrm{CaSO}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O}(\mathrm{s})\)

When \(\mathrm{CaSO}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O}(\mathrm{s})\), or gypsum, is heated, it loses water and forms a plaster of Paris. This is a type of dehydration reaction. The equation is:\[\mathrm{CaSO}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O}(\mathrm{s}) \rightarrow \mathrm{CaSO}_{4} \cdot \frac{1}{2} \mathrm{H}_{2} \mathrm{O}(\mathrm{s})+ \frac{3}{2} \mathrm{H}_{2} \mathrm{O}(\mathrm{g})\]

Key concepts

Thermal Decomposition

Thermal decomposition involves breaking down a compound by applying heat. This type of reaction is common in chemistry and is crucial for understanding how substances change form when heated. When a compound undergoes thermal decomposition, it typically breaks down into two or more simpler substances. Unlike other types of reactions, thermal decomposition requires energy input in the form of heat.
For instance, when magnesium bicarbonate (\( \operatorname{Mg}\left(\mathrm{HCO}_{3}\right)_{2}\)) is heated, it decomposes into magnesium oxide (MgO), water (H2O), and carbon dioxide (CO2), using energy supplied by heat. The formula is:
\[\operatorname{Mg}\left(\mathrm{HCO}_{3}\right)_{2}(\mathrm{s}) \rightarrow \operatorname{MgO}\left(\mathrm{s}\right) + \mathrm{H}_{2}\mathrm{O}(\mathrm{g}) + 2 \mathrm{CO}_{2}(\mathrm{g})\]
Understanding this reaction provides a base for deeper studies into material properties and chemical stability under heat.

Electrolysis

Electrolysis is a fascinating process where electrical energy is used to break down a compound into its constituent elements. This occurs in a liquid or molten form, allowing ions to move freely. In the context of chemistry, electrolysis is essential for extracting elements like metals from their compounds and occurs in an electrolytic cell.
When barium chloride (\( \mathrm{BaCl}_{2} \)) is subjected to electrolysis, it decomposes into barium (Ba) and chlorine gas (Cl2). Here's the reaction:\[ \mathrm{BaCl}_{2}(l) \rightarrow \mathrm{Ba}(s) + \mathrm{Cl}_{2}(g) \]
Electrolysis is a critical industrial process, often used in the metal industry to purify metals or in the generation of hydrogen gas. In simple terms, it turns a compound back into its original elements using electricity.

Neutralization Reactions

Neutralization reactions occur when an acid and a base react to form water and a salt. These reactions are vital as they result in a neutral product with a pH of around 7. The classic example of a neutralization reaction is the reaction between hydrochloric acid and sodium hydroxide, producing salt and water.
In our exercise, when calcium hydroxide (\( \mathrm{Ca(OH)}_2 \)) is added to sulfuric acid (\( \mathrm{H}_2\mathrm{SO}_4 \)), the reaction produces calcium sulfate (\( \mathrm{CaSO}_4 \)) and water, as shown:\[ \mathrm{Ca(OH)}_{2}(\mathrm{aq}) + \mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq}) \rightarrow \mathrm{CaSO}_{4}(\mathrm{aq}) + 2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \]
This process has practical applications, such as in medicine and environmental science, for controlling pH levels or in antacid formulations. Understanding neutralization helps us appreciate the balance in chemical reactions.

Displacement Reactions

Displacement reactions are interesting because they involve swapping elements within compounds. One element replaces another in a compound, producing a new element and a new compound. These reactions are characterized by their ability to show the activity series of metals, where a more reactive metal displaces a less reactive one.
For example, when strontium (\( \mathrm{Sr} \)) is added to hydrobromic acid (\( \mathrm{HBr} \)), it displaces hydrogen, leading to strontium bromide (\( \mathrm{SrBr}_2 \)) and hydrogen gas (\( \mathrm{H}_2 \)). The equation is:\[ \mathrm{Sr}(s) + 2 \mathrm{HBr}(aq) \rightarrow \mathrm{SrBr}_{2}(aq) + \mathrm{H}_{2}(g) \]
Displacement reactions are significant in metallurgy and are used to extract metals from their ores. They serve as a reminder of the dynamic interactions present in chemical processes and the reactivity of different elements.