Front

Definition of Physical Change

Back

Does not affect chemical composition

Answer explanation

A physical change is defined as a change that does not alter the chemical composition of a substance, meaning the substance remains the same at the molecular level, unlike chemical changes that create new substances.

Front

Example of a chemical change

Back

Rust forming on iron

Answer explanation

Rust forming on iron is a chemical change because it involves a reaction between iron and oxygen, resulting in a new substance (iron oxide). In contrast, melting ice, boiling water, and dissolving sugar are physical changes.

Front

Property of solids

Back

Definite shape and volume

Answer explanation

Solids have a definite shape and volume, meaning they maintain their form and do not conform to the shape of their container, unlike liquids and gases which have variable shapes and volumes.

Front

Energy transformation in chemical reactions

Back

Energy is conserved but can be transformed between different forms.

Answer explanation

During a chemical reaction, energy is conserved, meaning it cannot be created or destroyed. However, it can change forms, such as from chemical energy to thermal energy, which is why the correct choice highlights this transformation.

Front

Application of chemical change

Back

Rusting iron

Answer explanation

Baking bread involves a chemical change as yeast ferments sugars, producing carbon dioxide and alcohol, which causes the dough to rise. This transformation alters the ingredients' chemical structure, unlike physical changes like melting ice.

Front

Indicators of a chemical reaction

Back

Changes in color, temperature, precipitate formation, gas production, changes in properties.

Answer explanation

Indicators of a chemical reaction include changes in color, temperature, formation of a precipitate, gas production, and changes in properties. These signs confirm that a chemical change has occurred.

Front

Difference between physical and chemical changes

Back

Physical changes do not alter chemical composition; chemical changes do.

Answer explanation

The correct choice highlights that physical changes do not change a substance's chemical composition, while chemical changes do. This distinction is fundamental in understanding the nature of these changes.

Front

Significance of energy transfer in chemical reactions

Back

Influences reaction types, rates, and feasibility.

Answer explanation

Energy transfer is crucial in chemical reactions as it determines the reaction types, influences their rates, and affects their feasibility. This makes the correct choice significant compared to the other options.

Front

Physical property of matter

Back

Density

Answer explanation

Density is a physical property of matter that describes how much mass is contained in a given volume. It is a key characteristic used to identify substances and differentiate between them.

Front

Melting of ice

Back

into water

Answer explanation

Melting of ice into water is a physical change because it involves a change in state from solid to liquid without altering the chemical composition of water.