reaction

Definition

In chemistry, a reaction is a process in which one or more substances (reactants) are transformed into one or more new substances (products). The substances involved in a reaction are called the reactants, and the new substances produced are called the products.

The reactants and products of a reaction are connected by an arrow, which indicates the direction of the reaction. The arrow can be read as "reacts to form" or "yields."

For example, the following reaction shows the decomposition of hydrogen peroxide into water and oxygen:

2 H2O2 → 2 H2O + O2
In this reaction, hydrogen peroxide (H2O2) is the reactant, and water (H2O) and oxygen (O2) are the products.
The speed of a reaction can be affected by a number of factors, including the temperature, concentration of the reactants, and the presence of a catalyst.
A catalyst is a substance that speeds up a reaction without being consumed in the reaction. For example, the enzyme catalase is a catalyst that speeds up the decomposition of hydrogen peroxide.

Reactions can be classified into different types, depending on the number of reactants and products involved. Some common types of reactions include:

Combination reactions: Two or more substances combine to form a single product.
Decomposition reactions: A single substance breaks down into two or more products.
Single-displacement reactions: One element replaces another element in a compound.
Double-displacement reactions: Two compounds exchange elements to form two new compounds.

Reactions are an important part of chemistry, and they play a role in many different processes, such as the burning of fuel, the digestion of food, and the production of chemicals.

How can the word be used?

The chemical reaction produced a new substance.

Different forms of the word

Noun:

a response to a situation or event.
a chemical or physical change brought about by the interaction of two or more substances.
a feeling or opinion that is the opposite of another feeling or opinion.

Etymology

The word "reaction" comes from the Latin word "reactio", which means "to act back".

The first recorded use of the word "reaction" in English was in the 14th century.

Question

What is a reaction?

AQA Science Exam Question and Answer

Question:

Define a chemical reaction and provide an example that demonstrates the key characteristics of a reaction, including reactants and products.

Answer:

A chemical reaction refers to the process in which substances, called reactants, undergo a transformation to form new substances, known as products. This involves the breaking and forming of chemical bonds between atoms, resulting in a rearrangement of atoms to create different molecules or compounds.

An illustrative example of a chemical reaction is the combustion of methane (CH4) in the presence of oxygen (O2) to produce carbon dioxide (CO2) and water (H2O). In this reaction, methane and oxygen are the reactants, while carbon dioxide and water are the products. The reaction can be represented as:

CH4 + 2O2 → CO2 + 2H2O.

This equation demonstrates how one molecule of methane and two molecules of oxygen react to yield one molecule of carbon dioxide and two molecules of water. The atoms in the reactants rearrange to form the new molecules in the products, showcasing the fundamental nature of chemical reactions.