Predict the product(s) and write a balanced equation for each of the following redox reactions: (a) Pentane \(\left(\mathrm{C}_{5} \mathrm{H}_{12}\right)+\) oxygen \(\longrightarrow\) (b) Phosphorus trichloride \(+\) chlorine \(\longrightarrow\) (c) Zinc + hydrobromic acid (d) Aqueous potassium iodide + bromine \(\longrightarrow\) (e) Write a balanced net ionic equation for (d).

Combustion reactions are a class of redox reactions where a substance reacts with oxygen, releasing energy in the form of light and heat. These reactions are characterized by the presence of a hydrocarbon (a compound consisting mainly of hydrogen and carbon) and oxygen as reactants. The typical products of a hydrocarbon combustion reaction are carbon dioxide \((\mathrm{CO}_2)\) and water \((\mathrm{H}_2\mathrm{O})\).

• Example: The combustion of pentane \((\mathrm{C}_5\mathrm{H}_{12}))\) in oxygen.

An unbalanced equation for the reaction is:\[\mathrm{C}_5\mathrm{H}_{12} + \mathrm{O}_2 \rightarrow \mathrm{CO}_2 + \mathrm{H}_2\mathrm{O}\]The balanced equation is:\[\mathrm{C}_5\mathrm{H}_{12} + 8\mathrm{O}_2 \rightarrow 5\mathrm{CO}_2 + 6\mathrm{H}_2\mathrm{O}\]Balancing involves ensuring the same number of each type of atom on both sides of the arrow.

Balancing chemical equations is crucial for complying with the law of conservation of mass, which states that matter cannot be created or destroyed in a closed system. Start by writing the unbalanced equation with the correct formulas of reactants and products. Adjust coefficients (numbers in front of chemical formulas) to balance the atoms on each side of the equation.

• Example: The reaction between phosphorus trichloride \((\mathrm{PCl}_3)\) and chlorine \((\mathrm{Cl}_2)\) to form phosphorus pentachloride \((\mathrm{PCl}_5)\)

The unbalanced equation is:\[\mathrm{PCl}_3 + \mathrm{Cl}_2 \rightarrow \mathrm{PCl}_5\]The balanced equation is:\[\mathrm{PCl}_3 + \mathrm{Cl}_2 \rightarrow \mathrm{PCl}_5\]In this case, the equation is already balanced as both sides have the same number of phosphorus and chlorine atoms.

Net ionic equations simplify chemical reactions by focusing on the ions participating directly in the reaction. To write a net ionic equation, follow these steps:

1. Write the balanced full ionic equation including all ions.
2. Identify and exclude spectator ions (ions that do not participate in the reaction).
3. Write the net ionic equation with only the ions and molecules directly involved.

Example: For the reaction between aqueous potassium iodide \((\mathrm{KI})\) and bromine \((\mathrm{Br}_2)\)

• The full balanced equation:

\[2\mathrm{KI} + \mathrm{Br}_2 \rightarrow 2\mathrm{KBr} + \mathrm{I}_2\]

• The ionic form is:

\[2\mathrm{K}^+_{(aq)} + 2\mathrm{I}^-_{(aq)} + \mathrm{Br}_2 \rightarrow 2\mathrm{K}^+_{(aq)} + 2\mathrm{Br}^-_{(aq)} + \mathrm{I}_2\]

• The net ionic equation removes potassium, a spectator ion:

\[2\mathrm{I}^-_{(aq)} + \mathrm{Br}_2 \rightarrow \mathrm{I}_2 + 2\mathrm{Br}^-_{(aq)}\]

Chemical reactivity refers to how easily a substance undergoes a chemical reaction. Different substances have varying reactivity depending on their electron configurations and the types of bonds they form. Highly reactive substances tend to readily form new compounds.

• For instance: Zinc \((\mathrm{Zn})\) reacts with hydrobromic acid \((\mathrm{HBr})\) to form zinc bromide \((\mathrm{ZnBr}_2)\) and hydrogen gas \((\mathrm{H}_2)\)

The balanced equation for this reaction is:\[\mathrm{Zn} + 2 \mathrm{HBr} \rightarrow \mathrm{ZnBr}_2 + \mathrm{H}_2\]Zinc's high reactivity with acids results in the release of hydrogen gas, demonstrating its chemical nature.