Question

Write balanced equations for the following reactions: (a) Hydrochloric acid reacts with calcium carbonate to form carbon dioxide and calcium chloride and water. (b) Liquid bromine reacts with solid potassium metal to form solid potassium bromide. (c) Gaseous propane \(\left(\mathrm{C}_{3} \mathrm{H}_{8}\right)\) burns in oxygen to form gaseous carbon dioxide and water vapor.

Short answer

(a) \( 2\text{HCl} + \text{CaCO}_3 \rightarrow \text{CO}_2 + \text{CaCl}_2 + \text{H}_2\text{O} \) (b) \( \text{Br}_2 + 2\text{K} \rightarrow 2\text{KBr} \) (c) \( \text{C}_3\text{H}_8 + 5\text{O}_2 \rightarrow 3\text{CO}_2 + 4\text{H}_2\text{O} \)

Step-by-step solution

Identify Reactants and Products (a)

The reaction involves hydrochloric acid (HCl) reacting with calcium carbonate (CaCO₃) to produce carbon dioxide (CO₂), calcium chloride (CaCl₂), and water (H₂O).

Write Unbalanced Equation (a)

Write the skeletal chemical equation for the reaction: \[\text{HCl} + \text{CaCO}_3 \rightarrow \text{CO}_2 + \text{CaCl}_2 + \text{H}_2\text{O}\]

Balance the Equation (a)

Balance each element in the equation: - Calcium (Ca): 1 on both sides.- Chlorine (Cl): 2 on both sides by adjusting HCl.- Hydrogen (H): 2 on both sides by adjusting HCl.- Oxygen (O): 3 on both sides in the products CO₂ and H₂O.Final balanced equation:\[2\text{HCl} + \text{CaCO}_3 \rightarrow \text{CO}_2 + \text{CaCl}_2 + \text{H}_2\text{O}\]Ensure each element has the same number of atoms on both sides.

Identify Reactants and Products (b)

Liquid bromine (Br₂) reacts with solid potassium metal (K) to form solid potassium bromide (KBr).

Write Unbalanced Equation (b)

Write the skeletal chemical equation for the reaction: \[\text{Br}_2 + \text{K} \rightarrow \text{KBr}\]

Balance the Equation (b)

Balance the bromine and potassium by ensuring that the number of each atom is equal on both sides:- Potassium (K): 2 on both sides.- Bromine (Br): 2 on both sides.Final balanced equation:\[\text{Br}_2 + 2\text{K} \rightarrow 2\text{KBr}\]

Identify Reactants and Products (c)

Gaseous propane (C₃H₈) burns in oxygen (O₂) to form gaseous carbon dioxide (CO₂) and water vapor (H₂O).

Write Unbalanced Equation (c)

Write the skeletal chemical equation for the propane combustion: \[\text{C}_3\text{H}_8 + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O}\]

Balance the Equation (c)

Balance each element in the equation:- Carbon (C): 3 on both sides, requires 3 CO₂.- Hydrogen (H): 8 on both sides, requires 4 H₂O.- Oxygen (O): Count 10 O's on the product side, balanced by 5 O₂ on reactant side.Final balanced equation:\[\text{C}_3\text{H}_8 + 5\text{O}_2 \rightarrow 3\text{CO}_2 + 4\text{H}_2\text{O}\]The equation is balanced when every element has the same number of atoms on both sides of the equation.

Key concepts

Understanding Chemical Reactions

Chemical reactions are processes by which substances, known as reactants, transform into different substances, known as products. This transformation occurs through the breaking and forming of chemical bonds. Chemical reactions can happen in a variety of contexts, from biological processes in living organisms to industrial manufacturing of products.

In a chemical reaction, atoms are not created or destroyed, only rearranged. Therefore, the number of each type of atom in the reactants must equal the number of each type in the products, adhering to the law of conservation of mass. This principle becomes essential when we balance chemical equations, as it ensures the quantities of each substance involved are accounted for correctly.

Recognizing the types of chemical reactions is also crucial for understanding their mechanisms and applications. Common types include:

• Combustion reactions, like the burning of propane in oxygen.
• Redox reactions, such as the reaction between bromine and potassium.
• Acid-base reactions, like the interaction between hydrochloric acid and calcium carbonate.

These reactions can often release or absorb energy, which is a key aspect in determining their feasibility and use in practical applications.

Exploring Stoichiometry

Stoichiometry is the field of chemistry that focuses on the quantitative relationships between the reactants and products in a chemical reaction. It is crucial for figuring out how much of one substance will react with a given amount of another, predicting the amounts of products formed, and calculating yields for chemical processes.

In stoichiometry, each component of a reaction is represented by a stoichiometric coefficient. These coefficients denote the ratio in which reactants combine and products form, which can be identified from a balanced chemical equation. For example, in the balanced equation for the combustion of propane:\[\text{C}_3\text{H}_8 + 5\text{O}_2 \rightarrow 3\text{CO}_2 + 4\text{H}_2\text{O}\]We can see that one molecule of propane reacts with five molecules of oxygen to produce three molecules of carbon dioxide and four molecules of water. Using these ratios is essential when solving practical chemistry problems, such as determining quantities needed for industrial reactions or calculating the expected yield of a reaction in the lab.

Stoichiometry also ties into other chemical concepts such as molarity, molality, and concentration, making it a foundational aspect of chemistry that assists in understanding and predicting the outcomes of chemical reactions.

Mastering Chemical Equations Balancing

Balancing chemical equations is a vital skill in chemistry. It ensures that chemical equations adhere to the law of conservation of mass, where the number of atoms for each element present in the reactants is equal to those in the products.

The process begins with writing a skeleton equation, where you identify the reactants and products. From there, you adjust coefficients to balance each element. It's important to note that subscripts (the small numbers in formulas) should not be altered to balance equations—only the coefficients in front.

Let's take the example of the reaction between hydrochloric acid and calcium carbonate:\[2\text{HCl} + \text{CaCO}_3 \rightarrow \text{CO}_2 + \text{CaCl}_2 + \text{H}_2\text{O}\]Here, each element in the reaction is balanced with a designated number. 2 hydrogen and 2 chlorine atoms come from hydrochloric acid, one calcium atom is maintained, and carbon and oxygen balance with carbonate and water.

• Keep tab of each element’s count through trials.
• Adjust coefficients accordingly.
• Reevaluate the balanced state of the equation after each adjustment.

This practice is instrumental not just to comply with chemical norms but to predict reactant needs and product yields accurately in both theoretical and practical chemical scenarios.