Physical vs. Chemical Changes — Reading Comprehension

Premium Resource

Grades

Standards

MS-PS1-2
MS-PS1-5

About This Reader

This engaging science reading passage is designed for grades 6-8 and aligns with NGSS standards MS-PS1-2 and MS-PS1-5. Students will explore the distinctions between physical and chemical changes in matter, with a focus on observable phenomena, underlying mechanisms, and real-world applications. The passage explains why phase changes (like melting and freezing) are physical changes, and challenges students with tricky examples to deepen their critical thinking. Key vocabulary is embedded and defined, and students can check their understanding with a multiple-choice quiz, writing prompts, and graphic organizers. The resource includes English and Spanish versions, a simplified differentiated passage, and audio integration to support diverse learners. This comprehensive package enables students to analyze cause-and-effect relationships in matter and connect these concepts to broader scientific principles.

CONTENT PREVIEW

chemical-change-2 — Comparison of physical and chemical changes

Matter is all around us, and it is constantly changing in different ways. Sometimes, these changes are easy to see, such as when ice melts into water on a hot day. Other times, changes are more complex, like when a bicycle left outside turns rusty after several rainy weeks. Scientists classify these changes as either physical changes or chemical changes, and understanding the difference is essential for studying the behavior of matter in our world.

How Physical Changes Work

A physical change alters the form or appearance of a substance, but does not create a new substance. The particles in the material are rearranged, but their internal structure remains the same. Common physical changes include changes of state—such as melting, freezing, evaporation, and condensation. For example, when water freezes at 0°C, the molecules slow down and lock into a solid structure, but the chemical identity of H₂O does not change. Physical changes are usually reversible, meaning the process can go backward. Tearing paper, dissolving sugar in water, and breaking a rock are all physical changes because no new substances are formed.

Understanding Chemical Changes

A chemical change, also known as a chemical reaction, occurs when particles combine or separate to form one or more new substances. This process changes the chemical identity of the material. Burning wood is a classic example: the wood reacts with oxygen, releasing energy as heat and light, and forms carbon dioxide, water vapor, and ash. Another example is iron rusting, where iron combines with oxygen and water to form iron oxide (rust). Chemical changes are often irreversible, though not always. Clues that a chemical change has happened can include color change, formation of a gas, temperature change, or a new odor.

Tricky Cases and Critical Thinking

Some changes can be tricky to classify. For instance, dissolving salt in water looks like a physical change because the salt seems to disappear. However, the salt can be recovered by evaporating the water, so no new substance forms—it's a physical change. Cooking an egg is a chemical change: the heat causes proteins to change shape and bond in new ways, forming a new substance that cannot return to its raw state. Scientists use evidence, such as reversibility and whether a new substance is formed, to decide which type of change has occurred.

Understanding the difference between physical and chemical changes helps scientists design better materials, solve environmental problems, and improve manufacturing processes. These concepts are also foundational for understanding larger scientific ideas, such as the conservation of mass and the interactions of matter and energy.

Interesting Fact:
Lightning can cause nitrogen and oxygen in the air to chemically react and form new compounds—demonstrating that natural phenomena can create chemical changes, not just human activities!

What is a physical change?

A change where the substance's form changes but no new substance is made.A change where a new substance is created.A change that cannot be reversed.A change caused only by heat.

Which of the following is a chemical change?

Ice melting in the sun.Tearing a sheet of paper.Burning a piece of wood.Water freezing in a tray.

What makes a chemical change different from a physical change?

Chemical changes form new substances.Physical changes are always hot.Physical changes cannot be reversed.Chemical changes are always visible.

What does 'reversible' mean in the context of changes?

Able to go back to the original state.Able to turn into a new substance.Only happens with water.It means something is broken.

In the passage, what is an example of a tricky case that is still a physical change?

Cooking an egg.Burning wood.Dissolving salt in water.Rusting iron.

What evidence do scientists look for to decide if a change is chemical or physical?

If the process is reversible and if a new substance is formed.If the object is large or small.The color of the object before the change.If the change happens quickly.

Which of these is NOT a sign of a chemical change?

A new odor appears.A color change occurs.It freezes or melts.A gas forms.

True or False: Freezing and melting are chemical changes.

TrueFalse

True or False: Rusting is an example of a chemical change.

TrueFalse

What is the main idea of the passage?

Matter can change in physical or chemical ways, and knowing the difference is important.All changes in matter are the same.Only scientists can see changes in matter.Physical changes are always dangerous.