Physical vs. Chemical Change
Melting ice is physical or chemical?
Physical (state change; no new substance)
Which subatomic particle has a positive charge?
Proton
Fizzing/bubbling usually means what is being produced?
Gas
When a chemical reaction happens, what happens to the total mass?
It stays the same (matter conserved)
What do we call the starting substances in an equation?
Reactants
A bike getting rusty is physical or chemical?
Chemical (new substance: iron oxide/rust)
Where are electrons located in an atom?
Outside the nucleus (electron cloud/energy levels)
Name TWO signs of a chemical reaction from your list.
Example: gas (bubbling), temperature change, smell change, color change, precipitate/new solid
In the balloon lab (bottle + balloon), if you weigh before/after, what should happen to mass?
Mass stays the same because it’s a closed system
What do we call the substances formed after the reaction?
Products
In the “hot ice” (sodium acetate) demo, crystals appear. Does that automatically mean a chemical reaction happened?
No—could be a physical change if it’s the same substance becoming visible/solid again
Atomic number tells you the number of what particles?
Protons
In the balloon lab, what is the BEST visual observation that a reaction happened?
CO₂ gas filling the balloon
What happens to atoms during a chemical reaction?
Atoms rearrange to form new substances; they don’t turn into new types of atoms
When balancing an equation, what can you change: subscripts or coefficients?
Coefficients (not subscripts)
What is the key difference between a physical change and a chemical reaction?
Chemical reactions make new substances; physical changes do not
Draw/describe a neutral hydrogen atom: how many protons, neutrons, electrons?
1 proton, 0 neutrons (most common H), 1 electron
What is a precipitate?
A new solid that forms when two solutions react
In rust formation (3O₂ + 4Fe → 2Fe₂O₃), what are the reactants and the product?
Reactants: oxygen (O₂) and iron (Fe)
Product: iron oxide (Fe₂O₃)
How many oxygen atoms are in 3CO₂?
6 oxygen atoms (3 × 2)
A classmate says: “A new solid formed, so it MUST be a chemical reaction.” What’s a better response using the hot-ice example idea?
Not always—a solid can form by crystallization of a substance that was already there (dissolved) and is now just visible again
An element has atomic number 8 and atomic mass 16. In a neutral atom, how many protons, neutrons, electrons?
8 protons, 8 neutrons, 8 electrons
Pick the BEST single piece of evidence that a chemical reaction happened in the balloon lab, and justify it in one phrase.
Gas production (CO₂) → shows a new substance formed
Which is true: “2 molecules of iron oxide weigh the same as 4 atoms of iron mixed with 3 molecules of oxygen” — true or false?
True, matter is conserved.
For N₂ + 3H₂ → 2NH₃, how many total N atoms and H atoms are on EACH side?
Left: N=2, H=6
Right (2NH₃): N=2, H=6