Chemical or Physical Change
Cutting paper in half
Physical change
How many total atoms are in CaCl₂?
3 atoms
Symbol:O
Oxygen
A reaction causes the surroundings to feel colder. What type of reaction is this?
endothermic
How many total atoms are in 2NaCl?
4
A substance bubbles and produces a gas when mixed with another substance. What type of change is this?
Chemical change
How many oxygen atoms are in 2H₂O?
2 oxygen atoms
Symbol: Na
Sodium
A reaction releases heat into the surroundings. What type of reaction is this?
Exothermic
How many oxygen atoms are in 3CaCO₃
9
Salt dissolves in water and can be recovered by evaporation.
Physical
How many total atoms are in Al₂O₃?
5
Symbol:Fe
Iron
In which type of reaction is energy absorbed from the surroundings?
Endothermic
How many total atoms are in Ca(OH)₂?
5 atoms (1 Ca, 2 O, 2 H)
A piece of metal reacts with oxygen and forms a new substance on its surface.
Chemical
How many total atoms are in 3CO₂?
9
Symbol: Mg
Magnesium
A student mixes chemicals and the container becomes warm. Explain what type of reaction occurred and why.
Exothermic (heat released)
How many total atoms are in 2Al₂(SO₄)₃?
34 atoms
A substance bubbles and produces a gas when mixed with another substance. What type of change is this and why?
Chemical change
How many total atoms are in 2Al₂(SO₄)₃?
34
Symbol: Pb
lead
Compare endothermic and exothermic reactions. What happens to energy in each?
Endothermic absorbs energy; exothermic releases energy
How many total atoms are in 3Ca₃(PO₄)₂?
39 atoms