# Stoichiometry: Introduction to Stoichiometry

#### Summary

This chemistry lecture will help to define mole ratios and introduce molar mass as a conversion factor in solving stoichiometry problems.

## Learning Goals

This activity is designed for students to define stoichiometry, describe the importance of mole ratio in stoichiometric calculations, and write a mole ratio relating two substances in a chemical equation.

## Context for Use

This is conducted in an open lecture style. Students are allowed to ask questions at any time and encouraged to contribute any answers or comments they have. Usually this is done in 45 minutes and no special equipment is needed. Please stress that solving stoichiometry problems depends on having a balanced chemical equation! Because this is lecture based, it can be modified to fit in any classroom environment.

**Subject**: Chemistry:General Chemistry:Chemical Reactions:Stoichiometry

**Resource Type**: Activities:Classroom Activity

**Grade Level**: High School (9-12)

## Description and Teaching Materials

Begin the class by providing a list of ingredients needed to make a cake (I usually just put this on the board). Then, ask the students to write down every possible combination of ratios within this recipe. For example, 1 box of cake mix is needed for every two eggs. Once they have completed this, explain that they just completed mole ratios for the basic chemical equation of making a cake. Continue by giving them a simple chemical equation and have them find all the combinations of ratios. Once they have completed this you can begin notes on mole ratios and how they pertain to stoichiometry. This is where a definition of stoichiometry is given and we go through more problems until students are comfortable with the concept of stoichiometric calculations.

## Teaching Notes and Tips

Students should have a firm background in conversion factors and balancing equations. They should also know the basic idea of a ratio. Sometimes it is nice to add a hands on demonstartion of making cake batter or even better, something they can eat after making. I have found that by comparing it to food they find at home they understand that stoichiometry is just like analyzing the ingredients of a recipe.

## Assessment

After the lecture students are given a worksheet with 8 chemical equations on it. They are asked to find all possible mole ratios for each equation. We complete the first one together, on the board, as a class.

## Standards

GRADE 9-12, II. PHYSICAL SCIENCE, B. Chemical Reactions, The student will describe chemical reactions and the factors that influence them. Benchmark: 1. The student will describe chemical reactions using words and symbolic equations.