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Questions and Answers
Which of the following best describes a physical change?
Which of the following best describes a physical change?
- It cannot be reversed in any situation.
- It alters one or more physical properties without changing the substance. (correct)
- It creates new substances with distinct properties.
- It only involves changes in chemical composition.
What happens to a substance during a chemical change?
What happens to a substance during a chemical change?
- It undergoes a process where no new substances are formed.
- The substance maintains its original properties.
- It can always be reversed to its original form.
- New substances are created with different properties. (correct)
Which example illustrates a physical change?
Which example illustrates a physical change?
- Burning a candle.
- Rusting of iron.
- Melting ice into water. (correct)
- Baking bread.
Why is the rusting of iron considered a chemical change?
Why is the rusting of iron considered a chemical change?
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Which process is an irreversible chemical change?
Which process is an irreversible chemical change?
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Study Notes
Physical Changes
- Physical change alters physical properties without changing the substance's identity.
- Characterized as reversible, allowing a return to the original state.
- Substances remain the same despite changes in form.
Examples of Physical Changes
- Melting Ice: Ice (H2O) transforms to liquid water, maintaining chemical identity.
- Tearing Paper: Results in smaller paper pieces; composition of paper remains unchanged.
- Dissolving Sugar: Sugar combines with water, remaining chemically sugar but in solution.
Experiments Demonstrating Physical Changes
- Freeze and melt an ice cube to observe change and reversal.
- Cut or fold paper to experience a physical change without altering its substance.
- Stir sugar into water to witness its dissolution while retaining its identity.
Chemical Changes
- A chemical change creates one or more new substances with distinct properties.
- Typically irreversible, impeding a return to the original substance.
- New substances formed possess different properties from the starting materials.
Examples of Chemical Changes
- Burning Wood: Wood converts to ash and smoke, creating new chemical substances.
- Rusting Iron: Iron reacts with oxygen and water to form iron oxide (rust).
- Baking a Cake: Ingredients react during baking, yielding a new edible product.
Experiments Demonstrating Chemical Changes
- Burn a small piece of paper (with adult supervision) to observe combustion and ash formation.
- Leave a metal object outside to rust, illustrating long-term chemical change.
- Mix vinegar and baking soda to create bubbles indicating a chemical reaction and new substance formation.
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