Physical or Chemical?
Ice melting into water — physical or chemical change?
physical change
What does the law of conservation of mass state?
Matter cannot be created or destroyed.
Is this equation balanced?
H₂ + Cl₂ → 2HCl
Yes
Define an open system.
Matter can enter or leave.
In the reaction H₂ + Cl₂ → 2HCl, what is the total number of atoms on each side?
4 atoms total (2 H + 2 Cl on both sides)
Metal rusting when left outside — physical or chemical?
chemical change
If 20 g of hydrogen reacts with 80 g of oxygen, what is the total mass of the product?
100 g
Balance this equation:
Na + Cl₂ → NaCl
2Na + Cl₂ → 2NaCl
Define a closed system.
No matter enters or leaves.
For 2H₂ + O₂ → 2H₂O, how many total atoms are on each side?
6 atoms total (4 H + 2 O on both sides)
Sugar dissolving in water — physical or chemical?
physical change
Why must equations be balanced?
To show that atoms (and mass) are conserved.
Balance this equation:
H₂ + O₂ → H₂O
2H₂ + O₂ → 2H₂O
A bottle sealed during a reaction is what kind of system?
Closed
Calculate the total atomic mass for both sides of
C + O₂ → CO₂.
(C = 12, O = 16)
Both sides = 44 amu
Reactants: 12 + 32 = 44
Products: 12 + 32 = 44
Burning a candle — physical or chemical?
chemical change
What happens to total mass in a closed system during a reaction?
It stays the same.
Is this Balance?:
C + O₂ → CO₂
Yes
Why might the mass appear to change in an open system?
Gases can escape into the air.
In 2Na + Cl₂ → 2NaCl, what is the total mass of reactants and products?
(Na = 23, Cl = 35)
Both sides = 116 amu
Reactants: 46 + 70 = 116
Products: 116
Explain why cutting paper is a physical change.
No new substance forms; only the shape and size change.
A reaction starts with 50 g of reactants and ends with 48 g of products in an open system. Where did the 2 g go?
It escaped as gas or vapor.
What must be the same on both sides of the equation for it to be balanced?
The number of each type of atom.
Why do scientists use closed systems when studying reactions?
To measure and prove conservation of mass accurately.
For 2H₂O₂ → 2H₂O + O₂,
what is the total number of atoms and total atomic mass?
(H = 1, O = 16)
Atoms: 8 total (4 H + 4 O each side).
Mass: 68 amu both sides (Conserved).