Exploring Changes in Matter

Aiden is observing a block of ice melting in the sun. He wonders, what is a physical change?

• A physical change is a change that does not affect the chemical composition of a substance.

• A physical change alters the chemical structure of a substance.

• A physical change involves a reaction that produces new substances.

• A physical change is a process that cannot be reversed.

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.

During a science experiment, Coldero observed that rust was forming on a piece of iron left outside. Which of the following is an example of a chemical change?

• Rust forming on iron

• Ice melting

• Water boiling

• Sugar dissolving in water

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.

During a science class, Riza and Noah were discussing the properties of different states of matter. Riza mentioned that solids have a specific characteristic. Can you identify that property?

• Variable shape and volume

• No fixed structure

• Fluid-like behavior

• 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.

During a science experiment, Kaylum and Aiden are observing what happens to energy during a chemical reaction. What do they discover?

• Energy is conserved but can be transformed between different forms during a chemical reaction.

• Energy is only transformed into heat during a chemical reaction.

• Energy is lost and cannot be recovered after a reaction.

• Energy is created during a chemical reaction.

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.

Vrisan and Devindra were discussing the changes they observed in their backyard. They noticed that the old bicycle left out in the rain was starting to rust. Can you list one application of a chemical change in everyday life based on their observation?

• Rusting iron

• Baking bread

• Melting ice

• Boiling water

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.

During a science experiment, Alexander observed several changes in the materials he was mixing. What are some indicators of a chemical reaction that he might notice?

• Changes in color, temperature, formation of a precipitate, gas production, and changes in properties.

• Change in the smell of the container

• Formation of a solid layer on the surface

• Increase in mass

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.

During a science experiment, Mohammed and Jared were discussing how do physical changes differ from chemical changes.

• Physical changes differ from chemical changes in that physical changes do not alter the chemical composition of a substance, while chemical changes do.

• Physical changes involve a change in state, while chemical changes do not.

• Chemical changes can be reversed easily, whereas physical changes cannot.

• Physical changes always result in new substances, while chemical changes do not.

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.

During a science experiment, Alexander and Aiden are investigating the significance of energy transfer in chemical reactions. What did they discover about energy transfer?

• Energy transfer is significant as it influences reaction types, rates, and feasibility.

• Energy transfer has no impact on chemical reactions.

• Energy transfer is irrelevant to reaction mechanisms.

• Energy transfer only affects physical changes, not chemical reactions.

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.

During a science class, Ramsumair asked his friends to name a physical property of matter.

• Volume

• Density

• Mass

• Color

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.

Ramsumair observed the melting of ice cubes in his drink on a hot day. Describe a situation where a physical change occurs.

• Melting of ice into water.

• Freezing of water into ice.

• Dissolving sugar in water.

• Burning wood to ash.

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.