Question

What is a gas evolution reaction? Give an example.

Short answer

A gas evolution reaction is a reaction where a gas is produced. An example is the reaction between hydrochloric acid and sodium carbonate, producing carbon dioxide gas.

Step-by-step solution

Define Gas Evolution Reaction

A gas evolution reaction is a chemical reaction in which a gas is produced as one of the products. These reactions can occur in various types of chemical processes, including combustion, acid-base reactions, and decomposition reactions.

Give an Example of a Gas Evolution Reaction

One common example of a gas evolution reaction is the reaction between hydrochloric acid (HCl) and sodium carbonate (Na2CO3). When these two compounds react, they form sodium chloride (NaCl), water (H2O), and carbon dioxide (CO2) gas. The chemical equation for the reaction can be written as: \[2 \text{HCl} + \text{Na}_2\text{CO}_3 \rightarrow 2 \text{NaCl} + \text{H}_2\text{O} + \text{CO}_2\]

Key concepts

Chemical Reactions

Understanding chemical reactions is fundamental to the study of chemistry. A chemical reaction involves the rearrangement of atoms and molecules to transform substances into new products. These reactions are driven by factors such as temperature, concentration, and pressure, among others. Most notably, chemical reactions adhere to the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction; instead, substances change forms. Various types of chemical reactions exist, including synthesis, decomposition, single displacement, double displacement, and combustion reactions. Examples can range from the simple combination of hydrogen and oxygen to form water, to the intricate processes that fuel our cells.

It's critical for students to recognize the signs of a chemical reaction, which may include a change in color, the formation of a precipitate, temperature changes, or the evolution of gas, the last of which is particularly germane to our exercise at hand.

Combustion Reactions

Combustion reactions are a type of chemical reaction where a substance combines with oxygen to release energy in the form of heat or light. Often associated with fire, combustion typically involves hydrocarbons reacting with oxygen to produce carbon dioxide, water, and energy. An everyday example includes the burning of natural gas in a stove. Considering combustion from a gas evolution standpoint, we focus on the production of water vapor and carbon dioxide gas as tangible byproducts. It's important to note that for combustion to occur, fuel, oxygen, and an ignition source are necessary, a concept crucial in understanding safety measures to prevent unintended or uncontrolled combustion.

Acid-Base Reactions

Acid-base reactions, also known as neutralization reactions, occur when an acid reacts with a base to produce water and an ionic compound known as a salt. The most well-known example of an acid-base reaction might be the reaction of hydrochloric acid with sodium hydroxide, creating sodium chloride and water. However, not all acid-base reactions are as straightforward. Many evolve a gas, often CO2, as demonstrated in the reaction between carbonate or bicarbonate salts and acids. Acids typically have a pH less than 7 and bases a pH greater than 7, with 7 being neutral. The concept of pH is a measure of the hydrogen ion concentration and is a critical aspect in the study of acid-base chemistry.

Decomposition Reactions

Decomposition reactions are the opposite of synthesis reactions. A single compound breaks down into two or more simpler substances. These reactions often require an input of energy in the form of heat, light, or electricity to occur. They are characterized by a complex compound, such as a carbonate or a chlorate, decomposing into simpler compounds when heated. For instance, calcium carbonate, when heated, decomposes to form calcium oxide and carbon dioxide gas - an important reaction in the manufacture of cement. With decomposition, students should acknowledge that these reactions may sometimes lead to the release of gases, turning them into gas evolution reactions.

Hydrochloric Acid and Sodium Carbonate Reaction

Examining the reaction between hydrochloric acid (HCl) and sodium carbonate (Na2CO3) provides a clear illustration of a gas evolution reaction. This reaction demonstrates how an acid reacts with a carbonate to produce carbon dioxide gas, water, and a salt - in this case, sodium chloride. The reaction can be visually identified by the bubbling of CO2 gas escaping the mixture, delineating it as a gas evolution reaction. This process is represented by the balanced chemical equation: \[2 \text{HCl} + \text{Na}_2\text{CO}_3 \rightarrow 2 \text{NaCl} + \text{H}_2\text{O} + \text{CO}_2\]In educational settings, this reaction also serves as an exemplary teaching moment to introduce the concept of stoichiometry, the study of quantitative relationships in chemical reactions, because the proportions of substances in this equation can be used to demonstrate the conservation of mass and the mole concept.