Chemistry: Physical vs Chemical Changes
Identify changes in matter and evidence of new substances
Chemistry: Physical vs Chemical Changes
Identify changes in matter and evidence of new substances
Chemistry - Grade 6-8
- 1
An ice cube melts into liquid water on a warm table. Is this a physical change or a chemical change? Explain your answer.
Think about whether a new substance forms.
This is a physical change because the water changes state from solid to liquid, but it is still water. - 2
A piece of paper is cut into many small pieces with scissors. Is this a physical change or a chemical change? Explain your answer.
This is a physical change because the paper changes size and shape, but the material is still paper. - 3
A metal bicycle chain is left outside in the rain and begins to rust. Is this a physical change or a chemical change? Explain your answer.
Rust has different properties from the original metal.
This is a chemical change because rust is a new substance that forms when the metal reacts with oxygen and water. - 4
A sugar cube dissolves in a cup of hot tea. Is this a physical change or a chemical change? Explain your answer.
A dissolved substance can often be recovered by evaporating the liquid.
This is a physical change because the sugar spreads out in the tea, but the sugar molecules are not changed into a new substance. - 5
Wood burns in a campfire and produces ash, smoke, heat, and light. Is this a physical change or a chemical change? Explain your answer.
This is a chemical change because new substances such as ash and gases form, and energy is released as heat and light. - 6
A glass cup breaks into several pieces when it falls. Is this a physical change or a chemical change? Explain your answer.
Breaking something does not always mean a new substance formed.
This is a physical change because the glass changes shape and size, but the broken pieces are still glass. - 7
Vinegar and baking soda are mixed in a cup. Bubbles quickly form and gas escapes. Is this a physical change or a chemical change? Explain your answer.
Gas production can be evidence of a chemical change when it is not caused by boiling.
This is a chemical change because bubbles of gas form as a new substance is produced during the reaction. - 8
A student sharpens a pencil, producing small wood shavings and a sharp point. Is this a physical change or a chemical change? Explain your answer.
This is a physical change because the pencil changes shape, but the wood and graphite do not become new substances. - 9
Milk is left out for several days and develops a sour smell. Is this a physical change or a chemical change? Explain your answer.
A new odor can be evidence that new substances formed.
This is a chemical change because the milk changes into substances with new properties, including a sour odor. - 10
A pot of water boils on a stove, and steam rises from the pot. Is this a physical change or a chemical change? Explain your answer.
This is a physical change because the water changes from liquid to gas, but it remains water. - 11
Classify each change as physical or chemical: tearing aluminum foil, frying an egg, melting butter, and fireworks exploding.
Look for changes in state or shape compared with signs of new substances and energy release.
Tearing aluminum foil is a physical change. Frying an egg is a chemical change. Melting butter is a physical change. Fireworks exploding is a chemical change. - 12
A student observes that two clear liquids are mixed and the container becomes warm. No flame is present. What evidence suggests a chemical change may have occurred?
The container becoming warm suggests a chemical change may have occurred because a temperature change can show that energy was released during a reaction. - 13
A crayon is melted and poured into a mold shaped like a star. After cooling, the crayon is solid again. Is this a physical change or a chemical change? Explain your answer.
Changing shape or state does not by itself create a new substance.
This is a physical change because the crayon changes state and shape, but it is still made of the same crayon material. - 14
A science class compares two changes. In Change A, salt water is left in a dish until only salt crystals remain. In Change B, a match burns and leaves black ash. Which change is physical and which is chemical? Explain.
Evaporation separates substances, while burning usually creates new substances.
Change A is a physical change because the water evaporates and the salt remains the same substance. Change B is a chemical change because burning produces new substances such as ash and gases. - 15
List three common signs that a chemical change may have happened. Then explain why one sign alone is not always enough proof.
Common signs of a chemical change include gas production, color change, temperature change, light production, odor change, and formation of a solid precipitate. One sign alone is not always enough proof because some physical changes can also show similar signs, such as bubbles forming when water boils.