Chemical Equations Chemical Equations IVIV
Chemical Equations Chemical Equations IVIV
Stoichiometric CalculationsStoichiometric Calculations
Coefficent in Balanced Equation
A. Gives the relative number of molecules of reactants and products.
Example: N2(g) + 3H2(g) --- > 2NH3(g)
One molecule of nitrogen gas molecules plus 3 molecules of hydrogen gas molecules forms 2 molecules of ammonia gas.
Coefficent in Balanced Equation
B. Gives the relative number of moles of reactants and products.
Example: N2(g) + 3H2(g) --- > 2NH3(g)
One mole of nitrogen gas reacts with 3 moles of hydrogen gas to produce 2 moles of ammonia gas
Law of Conservation of Mass Mass of reactants = Mass of product
Example: N2(g) + 3H2(g) --- > 2NH3(g)
2(14.0 g/mol) + 6(1.01 g/mol) = 2(14.0g/mol) + 6(1.01 g/mol)
34.06 g/mol = 34.06 g/mol
Steps to a Correct Answer
1. Write a balanced equation.2. Write a dimensional analysis set-up with labeled values. Start with given
value in problem.3. Don’t do work in parts. I want to see
one step.4. Calculate answer
Stoichiometry I
Type:
Mole-Mole
moles of ---> moles of reactant product
• Use coefficients in balanced equation
• Put moles of chemical you’re solving for in the numerator.
Example 1. Mole-Molestart with mole – end with mole
How many moles of nitric oxide (nitrogen monoxide) are produced when 0.500 moles of nitrogen reacts with excess nitrogen?
Step 1: N2(g) + O2(g) --- > 2NO(g)
Step 2: Start with the given value. Write mole ratio using coefficients in balanced equation. Put the number of moles of the substance you’re solving for in the numerator.
0.500 mol N2 x 2 mol NO 1 mol N2
Step 3: Answer: 1.00 mol NO
Stoichiometry II
Type: Mass – Mole
mass of ---> moles of reactant product
• Change mass of chemical given to moles using it’s molar mass.
• Mole ratio from balanced equation. Put moles of chemical you’re solving for in numerator.
Example 2. Mass-Molestart with mass – end with mole
C2H5OH(ℓ) + 3O2(g) ---- > 2CO2(g) + 3H2O(ℓ)
How many grams of CO2 are produced when 3.00 g of C2H5OH is burned?
3.00 g C2H5OH X 1 mol C2H5OH X 2 mol CO2
46.08 g C2H5OH 1 mol C2H5OH
Answer: 0.130 mol CO2
Stoichiometry III
Type:
Mass – Mass
mass of ---> mass of reactant product
• Change mass to moles using molar mass
• Use mole ratio from balanced equation. Put moles of chemical you’re solving for in the numerator.
• Change moles to mass using molar mass
Example 3. Mass – Massstart with mass – end with mass
2 C8H18(ℓ) + 25 O2(g) ---- > 16 CO2(g) + 18 H2O(ℓ)
How many grams of O2 are needed to burn 2.00 g of C8H18?
2.00 g C8H18 X 1 mol C8H18 X 25 mol O2 x 32.0 g O2
114.26 g C8H18 2 mol C8H18 1 mol O2
Answer: 7.00 g O2
Stoichiometry IV
Type:
Moles – Mass
moles of ---> mass of reactant product
• Change mass of given chemical to moles using molar mass
• Use mole ratio from balanced equation putting moles of chemical you’re solving for in numerator.
• Change moles to mass using molar mass
Example 4. Moles to Massstart with moles – end with
mass
2 C4H10(ℓ) + 13 O2(g) ---- > 8 CO2(g) + 10 H2O(ℓ)
How many grams of CO2 are produced when 1.72 x 10-2 moles of
C4H10 burns in air?
1.72 x 10-2 mol C4H10 X 8 mol CO2 X 44.01 g CO2
2 mol C4H10 1 mol CO2
Answer: 3.03 g CO2