Chemical Reactions

Reactants vs. Products

compounds/elements on the left; they are

“reacting”

compounds/elements on the right; they are

“produced”

Reaction symbol

Meaning Example

“yields”

what is on the left is transformed to what is on the right.

# of atoms of one element on the left must be equal to # of atoms on the right.

2Al2O3 4Al + 3O2

4 Al 4 Al 6 O 6 O

Reaction symbol

Meaning Example

↔ or ⇌Still read as “yields”

However these arrows indicate that the reaction can go either way; it is reversible.

When salt dissolves:NaCl ⇌ Na+ + Cl-

You can get the salt back, so it’s reversible

Blue Fugates of Troublesome Creek

Reaction symbol

Meaning Example

(s) (l) (g) (aq)

These are the states of matter: solid, liquid, gas, aqueous

Aqueous – solution in water

NaOH(aq) + HCl(aq) H2O(l) + NaCl(aq)

This reaction takes place in water.

We know that there is not precipitate formed or gas evolved.

Reaction symbol

Meaning Example

∆

Greek letter “delta”

When above a reaction arrow it means that heat is put in the reaction. Can also be on either side of the arrow to show that heat is put in the rxn or given off

C6H12O6 + O2 H2O + CO2 + ∆

This shows that when sugar is burned, heat is given off as a product.

Class DataMass Before (g) Mass After (g) Mass Difference (g)

Law of Conservation of Mass

• Stated by Lavoisier in the 18th century• Total mass of substances in a chemical

reaction does not change• Ex: C6H12O6 + 6O2 6CO2 + 6H2O

180g glucose + 192g oxygen 264g carbon dioxide + 108g water 372g material before 372g material after

amount input = amount output