Question

Write a balanced chemical equation for each chemical reaction. (a) Gaseous acetylene \(\left(\mathrm{C}_{2} \mathrm{H}_{2}\right)\) reacts with oxygen gas to form gaseous carbon dioxide and gaseous water. (b) Chlorine gas reacts with aqueous potassium iodide to form solid iodine and aqueous potassium chloride. (c) Solid lithium oxide reacts with liquid water to form aqueous lithium hydroxide. (d) Gaseous carbon monoxide reacts with oxygen gas to form carbon dioxide gas.

Short answer

Balanced chemical equations: (a) \(2\mathrm{C}_{2} \mathrm{H}_{2}(g) + 5\mathrm{O}_{2}(g) \rightarrow 4\mathrm{CO}_{2}(g) + 2\mathrm{H}_{2}\mathrm{O}(g)\), (b) \(\mathrm{Cl}_{2}(g) + 2\mathrm{KI}(aq) \rightarrow \mathrm{I}_{2}(s) + 2\mathrm{KCl}(aq)\), (c) \(\mathrm{Li}_{2}\mathrm{O}(s) + \mathrm{H}_{2}\mathrm{O}(l) \rightarrow 2\mathrm{LiOH}(aq)\), (d) \(2\mathrm{CO}(g) + \mathrm{O}_{2}(g) \rightarrow 2\mathrm{CO}_{2}(g)\).

Step-by-step solution

Balance reaction for acetylene with oxygen

Begin by writing the unbalanced equation for acetylene \textbf{combusting} with oxygen to produce carbon dioxide and water. The unbalanced reaction is: \[ \mathrm{C}_{2} \mathrm{H}_{2}(g) + \mathrm{O}_{2}(g) \rightarrow \mathrm{CO}_{2}(g) + \mathrm{H}_{2}\mathrm{O}(g) \]Balance the carbon atoms by having the same number of carbon atoms on both sides. Next, balance the hydrogen atoms. Finally, balance the oxygen atoms by adjusting the coefficient of oxygen gas.

Balance reaction for chlorine gas with potassium iodide

Write the unbalanced chemical reaction for chlorine gas reacting with aqueous potassium iodide to form solid iodine and aqueous potassium chloride. The unbalanced equation is: \[ \mathrm{Cl}_{2}(g) + \mathrm{KI}(aq) \rightarrow \mathrm{I}_{2}(s) + \mathrm{KCl}(aq) \]Balance the iodine atoms by ensuring the same number of iodine atoms exists on both sides of the equation. Then, balance the chlorine atoms. The potassium atoms should naturally balance out if iodine and chlorine are balanced.

Balance reaction for lithium oxide with water

List the unbalanced equation for solid lithium oxide reacting with liquid water to produce aqueous lithium hydroxide. The chemical equation is: \[ \mathrm{Li}_{2}\mathrm{O}(s) + \mathrm{H}_{2}\mathrm{O}(l) \rightarrow \mathrm{LiOH}(aq) \]Balance this reaction by adjusting coefficients to ensure that the number of lithium and oxygen atoms is the same on both sides of the equation. The hydrogen atoms typically balance out when oxygen is balanced.

Balance reaction for carbon monoxide with oxygen

Enter the unbalanced chemical equation for carbon monoxide reacting with oxygen gas to form carbon dioxide gas. The unbalanced equation is: \[ \mathrm{CO}(g) + \mathrm{O}_{2}(g) \rightarrow \mathrm{CO}_{2}(g) \]To balance this equation, ensure that the number of carbon atoms match on both sides and adjust the coefficient in front of oxygen gas to balance the oxygen atoms.

Key concepts

Chemical Reaction

A chemical reaction involves the rearrangement of atoms to form new substances. This happens when reactants combine or decompose to create products, each of which has distinct properties from the original materials. For example, when gaseous acetylene reacts with oxygen, two new substances are formed: carbon dioxide and water - both gases and different from the reactants in terms of chemical properties.

In the reaction, the starting substances, known as reactants, transform into the ending substances, called products. Understanding how to write and balance these reactions is crucial, as it gives insight into how much of each reactant is needed to form a certain amount of product, which is fundamental in fields like chemistry and industrial engineering.

Stoichiometry

Stoichiometry is the aspect of chemistry that deals with determining the relative quantities of reactants and products in chemical reactions. It is an essential tool for chemists and engineers as it provides the mathematical relationships between those elements and compounds involved in a reaction.

Example of Stoichiometry:

In the reaction where chlorine gas reacts with aqueous potassium iodide, not only do we need to know which substances react and what products form, but also in what amounts.

To predict these amounts, a balanced equation is used to interpret the mole ratios of reactants and products. This ratio is derived from the coefficients of a balanced chemical equation, which reflect the proportion by which these substances interact. Stoichiometry, therefore, allows us to calculate how much iodine will be produced from a given amount of chlorine gas, which has broad applications from laboratory work to commercial manufacturing.

Law of Conservation of Mass

The law of conservation of mass states that mass in an isolated system is neither created nor destroyed by chemical reactions or physical transformations.

According to this law, the mass of the reactants in a chemical reaction must equal the mass of the products. For instance, when solid lithium oxide reacts with liquid water to form aqueous lithium hydroxide, the sum of the mass of lithium oxide and water before the reaction will be the same as the mass of lithium hydroxide produced. This is why we balance chemical equations—to ensure that the atom count for each element is the same on both sides of the reaction, aligning with the law of conservation of mass.

If you look at the balanced equations from the provided exercise, you'll notice that the number of each type of atom is conserved from the reactants to the products. This core principle underpins all stoichiometric calculations in chemistry.

Combustion Reaction

A combustion reaction is a specific type of chemical reaction where a fuel and an oxidant (typically oxygen) react to form products and release energy, usually in the form of heat and light. Combustion reactions are ubiquitous and can be observed in everyday life, from the burning of wood in a fireplace to the reaction that powers internal combustion engines in cars.

An example of a combustion reaction is the burning of gaseous carbon monoxide with oxygen gas to produce carbon dioxide. This reaction must be properly balanced to respect stoichiometry and the law of conservation of mass. Combustion reactions are often exothermic, meaning they release heat. In the case of the combustion of acetylene with oxygen to form carbon dioxide and water, a significant amount of energy as heat is released, which is the basis for acetylene torches used in welding. Balancing combustion reactions is also fundamental in ensuring the safe and efficient operation of energy-generating processes.