Stoichiometry

Question 1

Stoichiometry

Answer 1

The study of the mass and the amount relationships between reactants and products in a chemical reaction.

• Uses a balanced equation.

Question 2

Mole Ratio

Answer 2

• The ratio of the amounts of entities in a chemical reaction.
• We can use mole ratios to determine amounts.

Ex. Magnesium metal reacts with hydrochloric acid to produce magnesium chloride in solution and hydrogen gas. What amount of hydrogen gas is produced when 3.3 mol of magnesium reacts?

Mg + 2HCl -> MgCl2 + H2

nH2 = 3.3 molmg x 1 molh2 / 1 molmg
= 3.3 mol H2

• 3.3 x 1 / 1

Question 3

Masses and Chemical Equations

Answer 3

• Chemists don’t directly measure reactants using moles!
• We do however already know how to convert back and forth between moles and mass.

Ex. A typical astronaut exhales 8.8x10^2 g of carbon dioxide daily. Determine the mass of lithium hydroxide required to react with this mass of CO2.

1. Convert mass to moles (n=m/M)
2. Use mole ratio (given x / )
3. Convert to mass (m = n x M)

Question 4

Things to Remember for Mass Relationships

Answer 4

1. Always start with a BALANCED chemical equation.
2. Convert mass (g) to moles.
3. Use mole ratios to convert entities (given x / ).
4. Convert moles back to mass (g).