Test: Chemical Reactions - Class 8 MCQ

The reaction 2Mg + O2 → 2MgO illustrates a redox reaction where magnesium is oxidized (gaining oxygen) and oxygen is reduced (losing electrons). Oxidation and reduction occur simultaneously, which is the defining characteristic of redox reactions.

While chemical reactions often involve changes in state, a change in the physical state of the reactants alone does not characterize a chemical reaction. Chemical reactions are identified by the formation of new substances, which may involve gas evolution, color changes, or precipitate formation.

In a double displacement reaction, ions from two different compounds exchange places to form two new compounds. This reaction often results in the formation of a precipitate or a gas.

A redox reaction is characterized by the simultaneous occurrence of oxidation and reduction processes. In these reactions, one species is oxidized (loses electrons), while another is reduced (gains electrons), making it essential in various chemical processes.

A combination reaction occurs when two or more substances combine to form a single new substance. The reaction of magnesium with oxygen to form magnesium oxide is a classic example of this type of reaction.

The reaction between sodium sulfate and barium chloride results in the formation of a white precipitate of barium sulfate. This is characteristic of a precipitation reaction where an insoluble solid separates from the solution.

Amylase is an enzyme that acts as a biocatalyst in living organisms, helping to catalyze the breakdown of starch into sugars. Enzymes are vital for various biochemical reactions in living systems.

Neutralization reactions are crucial for balancing pH levels. For example, antacids neutralize excess stomach acid to alleviate discomfort, while farmers use neutralization to adjust soil acidity for better crop yields.

A chemical reaction is defined as a process where one or more substances change into new substances. This transformation occurs when the atoms of the reactants rearrange to form different products, which may exhibit different physical and chemical properties.

Thermal decomposition refers to the process in which a compound breaks down into simpler substances when heated. For example, calcium carbonate decomposes into calcium oxide and carbon dioxide when heated.

A catalyst is a substance that accelerates the rate of a chemical reaction without undergoing any permanent change itself. This means it can participate in the reaction but is not consumed by it.

Effervescence is commonly observed during acid-base reactions when gas is produced. For example, when an acid reacts with a carbonate, carbon dioxide gas is released, leading to bubbling or fizzing.

A negative catalyst, or inhibitor, slows down the rate of a chemical reaction without being consumed in the process. This can be useful in controlling reactions in various industrial and biochemical applications.

In a displacement reaction, one element takes the place of another element in a compound, typically involving a more reactive element displacing a less reactive one. This is common in reactions between metals and acids.

The electrolysis of water is a decomposition reaction caused by electricity, where water is broken down into hydrogen and oxygen gases. This process demonstrates how electrical energy can induce a chemical change.

In a combination reaction, two or more reactants combine to form a single product, which may have a different physical state than the reactants. For instance, gases can combine to form a liquid or solid.

Amphoteric oxides are unique in that they can react with both acids and bases to produce salts and water. Examples include zinc oxide and aluminum oxide, which are versatile in their chemical behavior.

In an exothermic reaction, heat energy is released into the surroundings. This can be observed in reactions such as combustion, where heat is produced, indicating that the reaction is exothermic.

Zinc is more reactive than hydrogen and can displace it from acids. This property makes zinc a commonly used metal in displacement reactions, particularly in the production of hydrogen gas.

A neutralization reaction occurs when an acid reacts with a base to produce salt and water. This type of reaction is fundamental in acid-base chemistry and has various practical applications, including in medicine and agriculture.