Chemical Calculations Prentice-Hall Chapter 12.2 Dr. Yager

Objectives Construct mole ratios from balanced chemical equations and apply these ratios in stoichiometric calculations. Calculate stoichiometric quantities from balanced chemical equations using units of moles, mass, representative particles and volume of gases at STP.

A mole ratio is a conversion factor derived from the coefficients of a balanced chemical equation and interpreted in terms of moles. In chemical calculations, mole ratios are used to convert between moles of reactant and moles of product, between moles of reactants, or between moles of products.

Mole Ratios N2(g) + 3H2(g) 2NH3(g) 1 mole of nitrogen reacts with 3 moles of hydrogen Mole ratios are used to convert between any two compounds:

Mole-Mole Calculation If you have 0.60 mol of N2, how much NH3 is produced? The ratios are:

Write the six mole ratios for: 4Al(s) + 3O2(g) 2Al2O3(s)

Write the six mole ratios for: 4Al(s) + 3O2(g) 2Al2O3(s)

How many moles of aluminum are needed to form 3.7 mol of Al2O3?

How many moles of aluminum are needed to form 3.7 mol of Al2O3?

Mass-Mass Calculation

Calculate the number of grams formed by reacting 5 Calculate the number of grams formed by reacting 5.4 grams of H2 with excess N2. N2(g) + 3H2(g) 2NH3(g)

N2(g) + 3H2(g) 2NH3(g) Calculate the number of grams formed by reacting 5.4 grams of H2 with excess N2.

Other Stoichiometric Calculations It all comes down to moles. If you want atoms, particles, etc. then multiply moles by 6.02x1023 If you want gas volume at STP then multiply moles by 22.4 liters. If you have volume divide by 22.4 L/mol to get moles Always use dimensional analysis to check units!

12.2 Solution Diagram

Problem-Solving Approach 12.2 Problem-Solving Approach

1. How many moles of water are produced when 2 1. How many moles of water are produced when 2.5 mol of O2 react according to the following equation? C3H8 + 5O2  3CO2 + 4H2O 2.0 2.5 3.0 4.0

1. How many moles of water are produced when 2 1. How many moles of water are produced when 2.5 mol of O2 react according to the following equation? C3H8 + 5O2  3CO2 + 4H2O 2.0 2.5 3.0 4.0

2. Nitrogen gas reacts with hydrogen gas to produce ammonia gas. N2(g) + 3H2(g)  2NH3(g) What volume of H2 is required to react with 3.00 L of N2, and what volume of NH3 is produced at 0°C? volume of H2 = 9.00 L, volume of NH3 = 6.00 L volume of H2 = 3.00 L, volume of NH3 = 3.00 L volume of H2 = 3.00 L, volume of NH3 = 6.00 L volume of H2 = 1.00 L, volume of NH3 = 1.50 L

2. Nitrogen gas reacts with hydrogen gas to produce ammonia gas. N2(g) + 3H2(g)  2NH3(g) What volume of H2 is required to react with 3.00 L of N2, and what volume of NH3 is produced at 0°C? volume of H2 = 9.00 L, volume of NH3 = 6.00 L volume of H2 = 3.00 L, volume of NH3 = 3.00 L volume of H2 = 3.00 L, volume of NH3 = 6.00 L volume of H2 = 1.00 L, volume of NH3 = 1.50 L

3. Automotive airbags inflate when sodium azide, NaN3, rapidly decomposes to its component elements via this reaction: 2NaN3  2Na + 3N2. How many grams of sodium azide are required to form 5.00 g of nitrogen gas? 11.61 g 17.41 g 7.74 g 1.36 g

3. Automotive airbags inflate when sodium azide, NaN3, rapidly decomposes to its component elements via this reaction: 2NaN3  2Na + 3N2. How many grams of sodium azide are required to form 5.00 g of nitrogen gas? 11.61 g 17.41 g 7.74 g 1.36 g