Physical or Chemical
This type of change occurs when ice melts into a liquid.
What is a physical change?
Two or more atoms chemically bonded together.
What is a molecule?
What do we call the substances present BEFORE a chemical reaction?
What are reactants
In a balanced equation, what must be equal on both sides?
The number of atoms of each element.
Does dissolving sugar in water usually create a new substance? Explain
No — it is a physical change. The sugar only dissolves in the water and can be extracted.
This type of change occurs when a nail rusts outdoors.
What is a chemical change?
How many TOTAL atoms are in H₂O? How many of each?
3 atoms: 2 hydrogen and 1 oxygen.
What do we call the substances formed AFTER a chemical reaction?
What are products?
Is H₂ + Cl₂ → 2HCl balanced? How many atoms are on each side of the equation?
Yes: 2 H and 2 Cl on each side.
What is the difference between a physical property and a chemical property?
Physical: observed without changing identity; chemical: describes ability to react and form new substances.
This type of change occurs when a glass bottle breaks into several pieces.
What is a physical change?
How many oxygen atoms are in CaCO₃?
3 oxygen atoms.
Name TWO possible signs of a chemical reaction.
Examples: gas formation, precipitate, color change, temperature/light change (context matters).
Is H₂ + O₂ → H₂O balanced? Explain.
No. Left: 2 H, 2 O. Right: 2 H, 1 O.
Why is a color change alone NOT proof of a chemical reaction?
Color can change through physical processes; consider multiple observations and substance identity.
A candle burning and the wax melting would be these types of changes.
Candle burning -- chemical
Wax melting -- physical
How many atoms of each element are in 2H₂O?
4 H atoms and 2 O atoms (6 total).
Bubbles form when vinegar and baking soda mix. What evidence suggests a reaction?
A gas is produced; the bubbling is evidence of gas formation.
Is 2Mg + O₂ → 2MgO balanced? Explain.
Yes. Both sides have 2 Mg and 2 O.
A sealed reaction starts with 50 g of reactants. What is the total mass of products?
50 grams
What type of change occurs when an egg cooks in a frying pan.
What is a chemical change?
Count each type of atom in 3Ca(OH)₂.
3 Ca, 6 O, 6 H (15 total).
A white solid forms when two clear solutions mix. What is this solid called?
What is a precipitate?
Is CH₄ + 2O₂ → CO₂ + H₂O balanced? Explain.
No. Left: 1 C, 4 H, 4 O. Right: 1 C, 2 H, 3 O.
Before mixing, two liquids are clear and 22°C. After mixing, they become cloudy and 31°C. What evidence supports a chemical reaction?
Cloudiness may indicate a precipitate; temperature rises 9°C, suggesting energy release. Together these support a reaction.