Name That Change
Ice melting into water — physical or chemical?
Physical Change?
What are all substances made of?
Atoms
The total mass before and after a reaction stays the same — what is this called?
The Law of Conservation of Mass/Matter
Name one kind of evidence that a chemical reaction occurred.
Gas, color change, temperature change, new substance, or odor.
What causes the fizzing in a bath bomb?
A chemical reaction producing gas (CO₂).
Baking soda and vinegar create bubbles — what kind of change is that?
Chemical Change
In a chemical reaction, what happens to atoms?
They rearrange to form new molecules.
You mix 10 g of baking soda with 20 g of vinegar. The total gas produced has a mass of 2 g. What should the remaining liquid and container weigh?
28 g (30 g total minus 2 g gas)
Why is color change alone not always proof of a chemical reaction?
It could just be a physical mixture or dilution.
What happens when hydrogen peroxide breaks down in elephant’s toothpaste?
It decomposes into water and oxygen gas — chemical reaction.
Salt dissolves in water. Is that a chemical reaction? Explain.
No — it’s a physical change because no new substance forms.
Describe what happens to atoms in this reaction: H₂ + O₂ → H₂O
Hydrogen and oxygen atoms rearrange to form water molecules.
Why might a reaction appear to lose mass?
Gas escaped into the air.
A white powder and clear liquid are mixed — bubbles form. What does this tell you?
A gas formed → chemical reaction occurred.
Why does the Taj Mahal change color over time?
Acid rain reacts chemically with the marble (chemical weathering).
Burning paper leaves ash and smoke. What evidence tells you this is a chemical reaction?
New substances form (ash, gas), color change, odor change, energy release.
True or False: Atoms can be created or destroyed in a chemical reaction.
What Law is this?
False — they’re conserved.
Law of Conservation of Mass/Matter
How could you design an experiment to prove that mass is conserved?
Measure reactants and products in a closed system (no gas escape).
If two liquids mix and the temperature drops, what does that suggest?
A chemical reaction that releases energy (exothermic).
Cooking food often produces new smells and colors — why?
Chemical reactions form new substances.
Steel wool rusts in air over time. Why is this NOT a physical change?
Iron reacts with oxygen to form a new substance (iron oxide).
If you start with 6 carbon atoms and 12 oxygen atoms, how many of each must be in the products?
6 carbon and 12 oxygen atoms — atoms are conserved.
If a chemical reaction in a sealed container produces bubbles, how does the total mass change?
It doesn’t change — gas is trapped, so mass stays constant.
When measuring properties to identify substances, what kind of properties should you look for?
Characteristic (intrinsic) properties like density, melting point, boiling point.
In a glow stick, two liquids mix and emit light — what kind of reaction is this?
A chemical reaction that releases energy as light (chemiluminescence).