ChemAtlas

Chapter 5

Stoichiometry

Moles are the hinge. Grams convert to moles through molar mass, moles convert between substances through the balanced equation, and moles convert to particles through Avogadro's number.

Avogadro's number

6.02214076 × 10²³

particles per mole

Gramswhat you weigh÷ molar massand × to go backMolesthe hinge× 6.022 × 10²³and ÷ to go backParticlesatoms or moleculesMoles A → Moles Busing the coefficients of the balanced equationg → mol → mol → g
Fig. 4Grams never convert straight to particles. Every path runs through moles, which is why the mole is the unit the whole chapter turns on.
Starting from
g

The map

grams  ⇄  moles  ⇄  particles

Every conversion in this chapter runs through moles in the middle. Grams to particles is never one step.

Mass

25g

Amount

0.14mol

Particles

8.4e22

Molar mass

180.157g/mol

from the exam's periodic table

Working

  1. 01Molar mass of C6H12O6180.157 g/mol
  2. 0225 g × (1 mol / 180.157 g)0.138768 mol
  3. 030.138768 mol × (6.022 × 10²³ / 1 mol)8.3568e+22 particles
  4. 04Reported to 2 significant figures, set by 25. Conversion factors and balanced coefficients are exact and do not limit the answer.