Question

State whether the following describes a physical or a chemical change: changing physical state, but not chemical formula.

Short answer

It describes a physical change.

Step-by-step solution

Understanding Physical and Chemical Changes

A physical change involves a change in the physical properties of a substance without altering its chemical structure. This can include changes in shape, size, phase (state), or other physical characteristics. In contrast, a chemical change results in the formation of new chemical substances, as it involves a change in the actual chemical structure of the materials involved.

Identifying the Change Type

The statement "changing physical state, but not chemical formula" directly indicates that the material undergoes a change in its physical state (e.g., solid to liquid, liquid to gas, etc.) but the chemical composition of the substance remains unaltered.

Conclusion on the Type of Change

Since the change described involves altering only the physical state, without changing the substance's chemical composition or formula, this is characterized as a physical change.

Key concepts

Chemical Change

A chemical change is a process in which substances combine or break apart to form new substances. Unlike physical changes, chemical changes alter the actual molecular structure and chemical composition of the material involved. This means that the original substances are transformed into different matter, often producing energy or heat, a change in color, the formation of a precipitate, or the emission of gas.
Examples of chemical changes include:

• Burning wood, which turns into ash and releases gases
• Rusting of iron, where iron reacts with oxygen to form iron oxide
• Cooking an egg, wherein heat causes proteins to denature and form new structures

It's essential to know that during a chemical change, the mass of the reactants equals the mass of the products, adhering to the Law of Conservation of Mass.
This concept is crucial in chemistry and helps us understand reactions that power everything from the simple act of lighting a match to complex industrial processes.

Physical Change

Physical change involves altering the physical properties of a substance without changing its chemical identity. This type of change can be observed without a substance going through a chemical reaction or forming new substances.
Common examples of physical changes include:

• Melting ice into water
• Boiling water into steam
• Crushing a can

Since physical changes do not alter the atomic arrangements or the chemical makeup of a substance, they are often reversible. For instance, water can freeze to form ice, and the ice can melt back into water.
Understanding physical changes is vital in fields such as physics and engineering, where manipulating the physical state and form of materials is often more practical than changing their chemical structure.

States of Matter

The states of matter refer to the distinct forms that different phases of matter take on. In everyday life, we interact primarily with three states: solid, liquid, and gas. Matter can transition between these states through physical changes.

• Solid: In this state, particles are closely packed together in a fixed structure, resulting in a definite shape and volume.
• Liquid: Here, particles are still close but can move past each other, giving liquids a definite volume but no fixed shape. They take the shape of their container.
• Gas: Particles are far apart and move freely. Gases have neither a definite shape nor volume and will expand to fill their containers.

There is also a fourth state called plasma, found in stars and lightning.

• Transitions between states, such as melting, freezing, boiling, or condensation, involve physical changes.
• No alteration in chemical composition occurs during state changes.

Comprehending states of matter is crucial for understanding the material world, influencing everything from weather patterns to the behavior of substances in various industrial applications.