This document provides an outline for a general chemistry course lecture on stoichiometry. It introduces key concepts like atomic mass units, moles, molar mass, reaction stoichiometry, limiting and excess reactants. Example problems are provided to illustrate how to calculate the number of atoms or moles of a substance, balance chemical equations, determine limiting reagents, and use stoichiometry to quantify reactants and products in a chemical reaction.

1. General Chemistry—
Stoichiometry
Instructor: Helen (Chihan) Huang

2. Reflective Question
• Quantify things
– Take 1 g of XYZ medicine?
– Quantification in Chemical
reaction

3. Outline
• Amount of Substances
• Reaction Stoichiometry

4. Amount of Substances
• Atomic Mass Units
– 1 a.m.u. = mass of one atom of 12C
– Masses of all elements are relative to this
• Avogadro Constant: The number of atoms/
molecules in one mole of substances
– NA=6.022*1023 mol-1
– 1 mole= 6.022*1023 of things
• Practice Problems:
– How many atoms are in 0.25 moles of helium?
• Avogadro number: 6.022*1023 in 12 g of 12C

5. Mass vs. Mole
• 1 mole (6.022*1023 ) of 12C = 12 g
• Practice Problem:
• Calculate molar mass of CO
• How many moles of carbon monoxide are in 25.5 g?

6. Stoichiometry
• Meaning of coefficients
– Relationship—amount of reagents & products
1H2 +
1
2
O2 1 H2O
– Atoms are conserved
• Practice:
2C + 1O2 2 CO
– Moles of different reactants are required to
produce 2 moles of CO?
Lego

7. Balance reaction equation
1. Balance weird guy first
2. Hydrogen or oxygen
3. Uncombined elements last
NH3 + O2 NO + H2O

8. Limiting and Excess Reactants/
Reagents
• Limiting Reagent:
– The one exhausted first
• Excess Reagent:
– The reactants remained
• Practice:
Q: Which one is Limiting
Reactant?
2NH3 +
5
2
O2 2 NO + 3H2O
4 mol 2.5 mol
Limiting reagent=?
Lego

9. Review Question
• What mass of ammonia can be produced from
56.0 g of nitrogen and 10.0 g of hydrogen?
MW: N2=28.0, H2=2.0 (g/mol)
1. Balance reaction equation
2. Calculate amount of given reagents
3. Identify limiting reagent