Chemical and Physical Changes — Answer Key
Part A: Fix the Sentence
Each sentence has an error. Rewrite it correctly on the line.
1. Fix the sentence:
When ice melts into water, the ice turns into a brand new substance with new properties.
Corrected: When ice melts into water, it stays the same substance — water — just in a different state.
Melting ice is a physical change because the water molecules stay the same; only the state changes from solid to liquid.
2. Fix the sentence:
Dissolving sugar in water creates a chemical change because the sugar disappears.
Corrected: Dissolving sugar in water is a physical change because the sugar particles spread out but stay sugar.
Sugar molecules mix evenly into water but do not change into something new — evaporating the water leaves the sugar behind.
3. Fix the sentence:
Cutting a piece of paper into smaller pieces makes a chemical change happen.
Corrected: Cutting a piece of paper into smaller pieces is a physical change because the paper is still paper.
Cutting only changes the shape and size of the paper; the material itself stays the same.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. When water freezes into ice, this is called a physical change because no new substance forms.
Freezing changes only the state of matter — liquid to solid — so it is a physical change.
2. Boiling water turns into water vapor, a gas; this state change is reversible because we can cool the vapor back into water.
Most physical changes like boiling and freezing can be reversed because the substance itself does not change.
3. When salt mixes evenly into water, the salt has dissolved in the water and forms a solution.
Dissolving is a physical change because the salt particles spread out among the water but do not become a new substance.
4. Folding a sheet of paper into an airplane changes its shape but not the material it is made of.
Folding only alters the shape of the paper; the paper itself stays the same, so it is a physical change.
Part C: Short Answer
Answer each question in one or two complete sentences.
1. Explain why melting an ice cube is a physical change for a Grade 5 science class.
Sample answer: Melting an ice cube is a physical change because the ice and the water are made of the same substance — water molecules. Only the state changes from solid to liquid; no new material is formed, and the water can be frozen again.
Physical changes affect form or state but do not produce a new substance, and they are usually reversible.
2. Give two examples of physical changes you might see at home and explain why each one is physical.
Sample answer: Cutting an apple into slices is a physical change because the apple pieces are still apple. Boiling water on the stove is a physical change because the water turns into vapor but is still water — it can be cooled back into liquid.
Physical changes alter only appearance or state, not the chemical identity of the substance.