Changes in Matter

Changes in Matter

Middle School

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Learning Objectives

• Define and differentiate between physical and chemical changes.

• Analyze properties to determine if a chemical reaction has occurred.

• Explain how atoms are rearranged in chemical reactions to form new substances.

• Apply the law of conservation of mass to physical and chemical changes.

Key Vocabulary

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Physical Change

This describes a change in a substance's form, but not in its chemical identity.

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Chemical Change

This change results in creating a new substance with new and different properties.

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Conservation of Mass

This principle states that matter is not created or destroyed during a chemical reaction.

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Reactant

A reactant is a substance that is present at the very start of a reaction.

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Product

A product is the new substance that is formed at the end of a reaction.

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Density

Density measures the amount of mass packed into a given volume of a substance.

Key Vocabulary

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Solubility

The ability of a substance to dissolve in another substance to form a solution.

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Flammability

The ability of a substance to burn or ignite, causing fire or combustion to occur.

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Melting Point

The specific temperature at which a solid substance completely changes its state to become a liquid.

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Boiling Point

The exact temperature at which a liquid substance turns into a gas or vapor.

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Odor

The distinctive or characteristic smell that is emitted by a particular substance in the air.

What Are Physical Changes?

• A physical change alters a substance's form, not its chemical identity.

• A change of state, like ice melting, is a common physical change.

• Bending, crushing, and dissolving are other examples of physical changes.

Multiple Choice

What is the definition of a physical change?

• It alters a substance's form but not its chemical identity.

• It creates a new substance with different chemical properties.

• It only occurs when a substance changes state, like melting.

• It is a change that cannot be reversed.

Multiple Choice

Why are bending a wire and melting an ice cube both classified as physical changes?

• They change the form of a substance, not its chemical identity.

• They are both examples of a substance changing state.

• They both require the addition of heat to occur.

• They are both changes that are difficult to reverse.

Multiple Choice

A student stirs a spoonful of salt into a cup of warm water until the salt is no longer visible. If the student boils the water away, a white powder is left behind. What does this experiment demonstrate?

• Dissolving was a physical change because the salt was still present in the water.

• Dissolving was a chemical change because the salt disappeared.

• The water chemically reacted with the salt to make it dissolve.

• Only changes of state like melting or boiling are physical changes.

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Identifying Substances by Properties

• Every pure substance has unique physical and chemical properties to identify it.

• Key physical properties like density and boiling point don't change the substance.

• Chemical properties, like flammability, describe how a substance can chemically change.

• Water’s boiling point is always 100^°C (212^°F), acting like its fingerprint.

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Multiple Choice

What is the primary purpose of studying a substance's unique physical and chemical properties?

• To determine the identity of the substance.

• To change the substance into something new.

• To measure the temperature of the substance.

• To increase the mass of the substance.

Multiple Choice

What is the fundamental difference between a substance's physical and chemical properties?

• A physical property can be observed without changing the substance, while a chemical property describes its ability to change.

• A physical property involves how a substance burns, while a chemical property relates to its density.

• A physical property describes a substance's color, while a chemical property describes its boiling point.

• A physical property is about chemical reactions, while a chemical property is about the state of matter.

Multiple Choice

A scientist measures an unknown clear liquid and finds that it boils at 100 °C. What is the most logical conclusion that can be drawn from this single observation?

• The liquid is likely water because its boiling point is a unique physical property.

• The liquid is flammable because boiling is a chemical change.

• No conclusion can be drawn from only one property.

• The liquid must be a mixture of different substances.

What Are Chemical Changes?

• A chemical reaction transforms reactants into new substances called products.

• Atoms of the reactants are rearranged to form the products.

• The new products have different properties from the original reactants.

Multiple Choice

What is the primary result of a chemical reaction?

• New substances called products are formed.

• The reactants are destroyed and disappear.

• The properties of the reactants stay the same.

• The atoms of the reactants are converted into energy.

Multiple Choice

What happens to the atoms of the reactants during a chemical reaction?

• They are rearranged to form the products.

• They are completely destroyed during the reaction.

• They are mixed together but do not change.

• They become part of a new, heavier element.

Multiple Choice

If you know that the atoms in a substance have been rearranged to form new substances, what must be true?

• The products have different properties than the original reactants.

• The total number of atoms has decreased.

• The products will weigh less than the reactants.

• The reaction can be easily reversed.

Detecting a Chemical Reaction

• A reaction occurs if substance properties change after interaction.

• Changes in density, melting point, or odor indicate a chemical reaction.

• Burning steel wool is a chemical reaction, forming a new substance.

Multiple Choice

What happens for a chemical reaction to occur?

• When the properties of a substance change after an interaction.

• When a substance is mixed with water.

• When a substance changes its shape or size.

• When a substance gets warmer or colder.

Multiple Choice

Which of the following changes would indicate that a chemical reaction has likely occurred?

• A change in the substance's shape.

• A change in the substance's size.

• A change in the substance's odor.

• A change in the substance's location.

Multiple Choice

The process of burning steel wool is described as a chemical reaction. What does this imply?

• The steel wool only changes its temperature.

• A new substance with different properties is formed.

• The steel wool only changes its shape.

• The steel wool becomes a part of the air.

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The Law of Conservation of Mass

• The law of conservation of mass states that matter is not created or destroyed.

• This means the total mass you start with is the same as the mass you end with.

• In a chemical reaction, atoms are just rearranged to form new substances.

• For example, 12g of carbon and 32g of oxygen make 44g of carbon dioxide (CO₂).

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Multiple Choice

What is the central principle of the law of conservation of mass?

• Matter is not created or destroyed in a reaction.

• Some types of matter can be easily created.

• The mass of a substance always changes over time.

• Atoms are destroyed during a chemical reaction.

Multiple Choice

If mass is always conserved, what happens to the atoms during a chemical reaction?

• The atoms of the reactants are rearranged to form new substances.

• Some of the atoms are destroyed, reducing the total mass.

• New atoms are created, increasing the total mass.

• The atoms are converted into pure energy.

Multiple Choice

A chemical reaction starts with 20 grams of one reactant and 90 grams of another. If the reaction goes to completion, what can be concluded about the mass of the products?

• The total mass of the products will be 110 grams.

• The total mass of the products will be 90 grams.

• The total mass of the products will be 20 grams.

• It is impossible to know the mass of the products.

Energy and Changes in Matter

• Every change in matter involves energy, and energy is always conserved.

• Thermal energy, the total energy of particles, flows from warmer to cooler matter.

• Changes can absorb thermal energy, like melting, or release it, like burning.

Multiple Choice

What is the fundamental rule for every change that happens to matter?

• Energy is always involved in the process.

• The matter always becomes colder.

• The matter always becomes a gas.

• The total amount of matter changes.

Multiple Choice

What is the relationship between thermal energy and two objects at different temperatures?

• It flows from the warmer matter to the cooler matter.

• It flows from the cooler matter to the warmer matter.

• It is created by the change in matter.

• It is destroyed by the change in matter.

Multiple Choice

If you hold an ice cube in your hand, what is the best explanation for what happens?

• Energy will move from the hand to the ice cube, causing it to melt.

• Energy will move from the ice cube to the hand, causing the hand to warm up.

• The ice cube will release thermal energy and become colder.

• The hand will absorb thermal energy and the ice will not change.

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Common Misconceptions

Misconception	Correction
Substances "disappear" after a reaction, like burning.	Atoms rearrange to form new substances (e.g., gases); they are not lost.
Dissolving salt in water is a chemical change.	It is a physical change; the salt can be recovered by evaporating the water.
Temperature and thermal energy are the same thing.	Temperature is the average kinetic energy of particles, while thermal energy is the total.

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Summary

• Physical changes alter form, not the substance itself.

• Chemical changes create entirely new substances with new properties.

• Identify chemical reactions by comparing properties before and after.

• In chemical reactions, atoms are rearranged into new molecules.

• Mass is conserved; matter is not created or destroyed.

• All changes in matter involve a transformation of energy.

Poll

On a scale of 1-4, how well do you understand how to use substance properties to identify chemical changes?

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• 4