Test: Chemical Reactions and Equations - SSC CGL MCQ

Physical changes are alterations that affect the physical properties of a substance without changing its chemical composition. An interesting fact is that physical changes can often be observed through changes in state, such as melting ice or boiling water, where the substance transitions between solid, liquid, and gas states without forming new substances.

Chemical changes involve transformations that lead to the creation of new substances with different chemical properties. For instance, when wood burns to produce ash and gases, or when iron rusts, there is a chemical change occurring. These alterations are typically irreversible and result in the formation of distinct substances.

The ripening of fruits is a classic example of a chemical change. During this process, enzymes within the fruit catalyze reactions that break down complex molecules into simpler ones, leading to changes in color, texture, and taste. This transformation is irreversible and results in the formation of new substances within the fruit.

A key characteristic of a chemical reaction is a change in state. When substances react to produce new substances, observable changes such as a change in state, color, evolution of a gas, or change in temperature can indicate that a chemical reaction has occurred. This transformation is a fundamental aspect of chemical reactions and is often used to identify when a chemical change has taken place.

Among the given options, a change in volume is not a common observation indicating a chemical reaction. While changes in color, evolution of gas, and changes in temperature are typical indicators of chemical reactions, changes in volume are not universally associated with chemical reactions, making it the correct choice in this context.

When magnesium ribbon undergoes a chemical reaction, it often results in the formation of a white powder known as magnesium oxide. This process typically involves the magnesium ribbon burning with a dazzling white flame, ultimately transforming into the white powder. The production of this white powder is a characteristic outcome of the chemical reaction involving magnesium ribbon.

The reaction between calcium oxide and water resulting in the production of slaked lime with the release of a large amount of energy is a classic example of a combination reaction. In a combination reaction, two or more substances combine to form a single product.

Decomposition reactions involve a single compound breaking down into simpler substances. These reactions often require an external source of energy such as heat, light, or electricity to facilitate the breakdown process.

Displacement reactions involve the exchange of ions between reacting substances, leading to the formation of new compounds. In scenarios where a more reactive substance replaces a less reactive one in a solution, it often results in the formation of a precipitate, which is a solid that forms and does not dissolve in the solvent.

In oxidation reactions, such as when magnesium changes into magnesium 2 ion, electrons are lost. This loss of electrons is a key characteristic of oxidation. Electrons are crucial in defining oxidation, where the substance that is oxidized loses electrons.

Physical change refers to alterations in physical properties such as color, density, hardness, and state of matter without affecting the chemical composition of the substance. An example of a physical change is melting ice, where the solid form changes to liquid without altering the chemical structure of water. This type of change can typically be reversed by adjusting temperature and pressure, making it distinct from chemical changes where new substances are formed.

The evolution of a gas is one of the observable indications that a chemical reaction has taken place. When certain substances react chemically, they may release gases as a byproduct. This gas evolution can signify that new substances have been formed through the rearrangement of atoms and bonds. In chemical reactions, the formation of gases can be a crucial clue to understanding the transformation of substances at the molecular level.

In oxidation reactions, electrons are lost. This is exemplified when a substance like magnesium changes into a magnesium 2 ion and loses two electrons. This loss of electrons is a key characteristic of oxidation reactions, where the substance undergoing oxidation loses electrons.

One key distinction between physical and chemical changes lies in their reversibility. Physical changes, such as melting ice or dissolving sugar in water, can typically be reversed by altering temperature or pressure. In contrast, chemical changes, like burning wood or rusting iron, are usually irreversible, as they involve the formation of new substances with different chemical properties.

A chemical reaction can be visually confirmed through the formation of a new substance. When substances react to produce entirely different substances with distinct properties, it serves as a clear indication that a chemical reaction has occurred. This transformation involves bond breaking or formation between atoms, leading to the creation of new compounds or elements, highlighting the essence of a chemical reaction.