# Stoichiometry A fancy name for using a balanced equation.

## Presentation on theme: "Stoichiometry A fancy name for using a balanced equation."— Presentation transcript:

Stoichiometry A fancy name for using a balanced equation

What you need….. 1 A + 4 B  2 C

The ratios can be used when Given: moles Find: mole Given: mlcs Find: mlcs Given: Liters Find: Liters (gases only)

2NH3  3H2 + 2N2 How to set up the ratio…….. Given: hydrogen Find: Nitrogen? Given ammonia Find Hydrogen? Given nitrogen Find ammonia?

2C2H6 +11 O2  4 CO2 + 12H2O Given: 15 moles of O2 Find: ? Moles of CO2

2C2H6 +11 O2  4 CO2 + 12H2O Given : 8 liters o f CO2 Find: Liters of H2O

Mixed Stoichiometry When what you are given and what you are asked to find are not the same unit OR when given grams and asked to find grams 3STEPS – 1. Take what you are given and convert it to moles – 2 Then use the ratio (from the balanced eq) to calculate the moles of what you want to find – 3. Take the answer to #2 and convert to the unit wanted.

2H2 + 1 O2  2 H2O 64 g H2 x 1 mole = 31.7 moles 2.02 g 31.7 moles H2 x 2 H2O = 31.7 moles H2O 2 H2 31.7 Moles H2O x 18.02 g = 570 grams 1.0 mol

2H2 + 1 O2  2 H2O Given: 64 grams of H2 reacting Find: grams of water produced 64 g H2 x 1 mole x 2H2O x 18.02 grams = 2.02 g 2 H2 1.0 mol

Percent Yield Actual yield x 100 = % yield Theoretical yield The theoretical yield is what you calculated using stoichiometry. Its what you expect to get. Someone has to tell you what the actual yield is before you can figure out % yield.

Exothermic Heat is PRODUCED (A product) A + B  C + Heat ( ) 10 KJ 20 KJ 5 KJ

Heat is absorbed/gained (A reactant) C + Heat ( ) -  D + X 50 cal 30 cal 40 cal Endothermic

Hess’s Law A + 2 B  C 3 A + 6 B -  3 C ½ A + 1 B  ½ C C  A + 2 B

Hess’s Law When adding up the steps to a chain rxn, you can add up their Delta H ( )

P + X  Z 2X  C NET: 2 P + C  2Z

B + C  D + E X + 2C  2D + P NET: X + 2E -  2B + P

Txt Problems. P209 #61 P4 + 3 O2  P4O6 P4 + 5 O2  P4O10 Net: P4O6 + 2 O2  P4O10