Evidence of Reaction
True or False — Melting ice is a chemical reaction.
False
True or False — Atoms are destroyed in a chemical reaction.
False → Atoms cannot be destroyed in chemical reactions.
If a reaction feels warm, is it exothermic or endothermic?
Warm → Exothermic (releases heat).
Is this equation balanced?
H₂ + O₂ → H₂O
Not balanced (needs 2H₂ + O₂ → 2H₂O).
What gas do humans breathe in that is necessary for survival?
Oxygen (O₂).
Which is the BEST evidence of a chemical change?
a) Ice melting
b) Paper burning
c) Sugar dissolving
d) Water boiling
Paper Burning
If a reaction starts with 10 g of reactants, how much product should form?
10 g of products → mass is conserved.
If a reaction feels cold, is it exothermic or endothermic?
Cold → Endothermic (absorbs heat).
Is this equation balanced?
H₂ + Cl₂ → 2HCl
Yes, it is balanced.
What force keeps the planets in orbit around the Sun?
Gravity
You mix vinegar and baking soda. What evidence shows a chemical reaction?
Gas bubbles forming CO2
Why does a sealed container help prove conservation of mass.
A sealed container keeps gases inside → total mass can be measured accurately.
Would you use an exothermic or endothermic reaction in a hand warmer?
Hand warmer → Exothermic (needs to give off heat).
Is this equation balanced?
N₂ + 2H₂ → 2NH₃
Not balanced (needs N₂ + 3H₂ → 2NH₃).
One year on Earth is the time it takes for Earth to complete what motion?
One revolution (orbit) around the Sun.
Two clear solutions are mixed. A yellow solid forms and sinks. What does this suggest?
New substance (precipitate) formed so a chemical reaction took place
In a chemical reaction, hydrogen and oxygen form water. What happens to the atoms?
The H and O atoms are rearranged to form water molecules but are not lost or gained.
Would you use an exothermic or endothermic reaction in an instant ice pack?
Ice pack → Endothermic (absorbs heat to feel cold).
s this equation balanced?
4Na + O₂ → 2Na₂O
Yes, it is balanced.
The Earth’s tectonic plates float on which layer of the Earth?
The mantle (specifically the asthenosphere).
A student says rusting is just “iron getting dirty.” Explain why that’s incorrect.
Rusting is a chemical reaction → iron reacts with oxygen to form iron oxide (new substance).
A student burns a piece of paper and says the mass is gone. Explain why this is wrong.
The atoms in the paper combine with oxygen → form CO₂ and H₂O vapor, which move into the air (mass is still there).
Why do endothermic reactions feel cold, and why do exothermic reactions feel hot?
Endothermic reactions absorb heat from their surroundings, making the surroundings feel colder.
Exothermic reactions release heat into their surroundings, making them feel warmer.
Is this equation balanced?
C₃H₈ + 4O₂ → 3CO₂ + 4H₂O
Not balanced (needs C₃H₈ + 5O₂ → 3CO₂ + 4H₂O).
What is the main gas in Earth’s atmosphere?
Nitrogen (about 78%).