Gas Evolution Equations (Simplified): Videos & Practice Problems

A gas evolution reaction occurs when carbon dioxide gas is produced from reactants, typically involving hydrogen ions (H⁺) and bicarbonate ions. The intermediate product, carbonic acid (H₂CO₃), loses a water molecule, resulting in CO₂ gas. This process illustrates the concept of acid-base reactions, where the Brønsted-Lowry acid donates protons, leading to gas formation. Understanding this reaction is crucial for grasping broader concepts in chemistry, such as reaction mechanisms and gas laws.

Gas Evolution Equations (Simplified) Concept 1

A gas evolution equation describes a chemical reaction that produces carbon dioxide gas (CO₂) as a result of the transformation of certain reactants. In this context, the term "medium product" refers to an intermediate product that forms before it fully converts into the final product. Specifically, in gas evolution reactions involving acids and bicarbonate ions, the medium product is carbonic acid (H₂CO₃).

When hydrogen ions (H⁺) react with bicarbonate ions (HCO₃^-), they form carbonic acid. However, carbonic acid is unstable and cannot exist in isolation; it quickly decomposes by losing a water molecule (H₂O). The reaction can be summarized as follows:

H⁺ + HCO₃^- → H₂CO₃ (medium product) → CO₂ (gas) + H₂O (liquid)

Similarly, when H⁺ reacts with carbonate ions (CO₃^2-), carbonic acid is again formed as the medium product, which subsequently decomposes to yield carbon dioxide gas and water:

H⁺ + CO₃^2- → H₂CO₃ (medium product) → CO₂ (gas) + H₂O (liquid)

In essence, the gas evolution equation illustrates how carbonic acid, while initially formed, ultimately leads to the production of carbon dioxide gas and water through the loss of a water molecule. This process highlights the dynamic nature of chemical reactions, where intermediate products play a crucial role in the formation of final products.

Gas Evolution Equations (Simplified) Example 1

To predict whether a reaction occurs between sodium carbonate and hydrobromic acid, we start by breaking down the reactants into their ionic forms. Sodium carbonate consists of sodium ions (Na⁺) and carbonate ions (CO₃^2-), while hydrobromic acid is made up of hydrogen ions (H⁺) and bromide ions (Br^-).

Next, we swap the ionic partners based on the principle that opposite charges attract. The sodium ion (Na⁺) pairs with the bromide ion (Br^-), forming sodium bromide (NaBr). Since both ions have charges that balance each other out, they combine directly. For the other pair, the hydrogen ion (H⁺) and the carbonate ion (CO₃^2-) combine by crisscrossing their charges, resulting in carbonic acid (H₂CO₃).

According to solubility rules, sodium bromide (NaBr) is soluble in water, while carbonic acid (H₂CO₃) is a transient product that decomposes into water (H₂O) and carbon dioxide gas (CO₂). This breakdown is crucial as it indicates the formation of a gas during the reaction.

Finally, we balance the molecular equation. Initially, we have 2 sodium ions on the reactant side, so we place a coefficient of 2 in front of NaBr. The carbon and oxygen atoms are balanced as there is 1 carbon and 3 oxygens on both sides. For the hydrogen and bromine, we adjust the coefficients to ensure that the number of each atom is equal on both sides of the equation. After balancing, the final equation reflects the stoichiometry of the reaction accurately.

The balanced molecular equation for the reaction is:

2 Na₂CO₃ + 2 HBr → 2 NaBr + H₂O + CO₂ (g)

Predict the products formed from the following gas evolution equation.

• A. KCl, H₂CO₃
• B. CO₂, H₂O
• C. KCl, CO₂, H₂O
• D. KCl, H₂, CO₃^2–

Answer: (C)

Here’s what students ask on this topic:

What is a gas evolution reaction in chemistry?

A gas evolution reaction in chemistry is a type of chemical reaction where a gas is produced as one of the products. A common example involves the reaction between hydrogen ions (H⁺) and bicarbonate ions (HCO₃^-), which forms carbonic acid (H₂CO₃) as an intermediate. This intermediate then decomposes to produce carbon dioxide gas (CO₂) and water (H₂O). These reactions are important for understanding acid-base chemistry and reaction mechanisms.

How is carbon dioxide gas formed in a gas evolution reaction?

In a gas evolution reaction, carbon dioxide gas (CO₂) is typically formed when hydrogen ions (H⁺) react with bicarbonate ions (HCO₃^-). This reaction produces carbonic acid (H₂CO₃) as an intermediate product. Carbonic acid is unstable and quickly decomposes, losing a water molecule (H₂O) to form carbon dioxide gas (CO₂). The overall reaction can be summarized as:

$H_2{\mathrm{CO}}_3\to {\mathrm{CO}}_2+H_2{O}_{}$

What are the reactants involved in a gas evolution reaction that produces CO₂?

The primary reactants involved in a gas evolution reaction that produces carbon dioxide (CO₂) are hydrogen ions (H⁺) and bicarbonate ions (HCO₃^-). When these ions react, they form carbonic acid (H₂CO₃) as an intermediate product. Carbonic acid is unstable and decomposes to produce CO₂ gas and water (H₂O). The reaction can be represented as:

$H_{+}$

Why is carbonic acid considered an intermediate product in gas evolution reactions?

Carbonic acid (H₂CO₃) is considered an intermediate product in gas evolution reactions because it is not stable and does not remain in its form for long. When hydrogen ions (H⁺) react with bicarbonate ions (HCO₃^-), carbonic acid is formed temporarily. However, carbonic acid quickly decomposes by losing a water molecule (H₂O) to produce carbon dioxide gas (CO₂). This rapid decomposition is why carbonic acid is seen as an intermediate rather than a final product in these reactions.

What is the role of hydrogen ions in gas evolution reactions?

Hydrogen ions (H⁺) play a crucial role in gas evolution reactions by reacting with bicarbonate ions (HCO₃^-) to form carbonic acid (H₂CO₃). This carbonic acid then decomposes to produce carbon dioxide gas (CO₂) and water (H₂O). The hydrogen ions essentially drive the reaction forward by facilitating the formation of the intermediate product, carbonic acid, which then breaks down to release CO₂ gas. This process is a key example of an acid-base reaction where the Brønsted-Lowry acid (H⁺) donates protons.