CH1000 Fundament als of Chemistry Module 2 – Chapter 9

Introduction to Stoichiometry

• Equations must always be balanced before calculation of any mass, moles, or volume of a reactant or product!

• Stoichiometry is the area of chemistry that deals with quantitative relationships between products and reactants in chemical equations.

• Solving stoichiometry problems always requires the use of: • A balanced chemical equation (coefficients must be known!) • Conversion factors in units of moles (mole ratios)

Mole Ratios

•Mole ratio is the conversion factor between any two species in a chemical reaction

•The mole ratio will come from the coefficients of a balanced chemical equation

Mole Ratios in Practice

•The mole ratio can be used as a conversion factor to convert between moles of one substance and another.

•The desired quantity goes in the numerator and the known quantity goes into the denominator of the mole ratio

•Same method as the solution map from chapter 2.

Problem Solving for Stoichiometry Problems

Problem Solving for Stoichiometry Problems

Problem Solving for Stoichiometry

Problems

•Remember that Step 1 is to always ensure you have a balanced equation!!!

•You must be in moles to convert from one substance to another!

Limiting Reactants •In chemical reactions, the reaction will occur until one of the reactants runs out

•Think of a burning fire. You need oxygen, heat and fuel to keep a fire going. If the fuel (wood) all burns, the fire goes out. The wood would be the limiting reactant because had it not all burned, the fire would continue to exist.

•In a chemical reaction, the maximum amount of product formed depends on the amount of reactant not in excess, the limiting reactant

Reaction Yield

• The amount of products formed calculated by stoichiometry are the maximum yields possible (100%)

• Yields are often lower in practice due to side reactions, loss of product while isolating/transferring the material, etc.

• The theoretical yield is the maximum possible yield for a reaction, calculated based on the balanced chemical equation.

• The actual yield is the yield obtained from the reaction

• The percent yield is the ratio of the actual and theoretical yield

Reading Review

What is stoichiometry?

What unit must you be in to convert from one substance to another?

What is the limiting reactant?

What is the difference between theoretical and actual yields?

How do you calculate the percent yield?

Slide 1
Introduction to Stoichiometry
Mole Ratios