Stoichiometry and Mole-to-Mole Calculations in GOB Chemistry

Stoichiometry

Introduction to Stoichiometry

Stoichiometry is the quantitative study of reactants and products in a chemical reaction. It allows chemists to predict the amounts of substances consumed and produced in a reaction using balanced chemical equations.

• Stoichiometry deals with the numerical relationship between compounds in a balanced chemical equation.

• It enables determination of the amount of products from reactants and vice versa.

• Balanced equations are essential for stoichiometric calculations.

Example Balanced Equation:

• $2\ H_2\ (g) + 1\ O_2\ (g) \rightarrow 2\ H_2O\ (g)$

• Given: 12.3 g $H_2$

Stoichiometric Chart and The Jump

Using the Stoichiometric Chart

The stoichiometric chart is a visual tool that helps convert the given quantity of a compound to the unknown quantity of another compound in a chemical reaction.

• Start with the Given quantity (could be grams, moles, atoms, formula units, or molecules).

• Convert the Given to moles using molar mass or Avogadro's number as appropriate.

• Use the coefficients from the balanced equation to perform a Mole to Mole Comparison ("The Jump").

• Convert moles of the Unknown to the desired units (grams, molecules, etc.).

Stepwise Stoichiometric Calculations

1. Step 1: Map out the portion of the stoichiometric chart you will use.

2. Step 2: Convert the Given quantity into moles of Given.

   • If a compound is in excess, ignore it for the calculation.

3. Step 3: Do a Mole to Mole comparison to convert moles of Given into moles of Unknown.

4. Step 4: If necessary, convert the moles of Unknown into the final desired units.

Key Terms and Definitions

• Mole: The amount of substance containing $6.022 \times 10^{23}$ entities (Avogadro's number).

• Molar Mass: The mass of one mole of a substance, expressed in grams per mole (g/mol).

• Coefficient: The number in front of a chemical formula in a balanced equation, indicating the relative number of moles.

Example Calculation

Question: How many grams of $H_2O$ are produced when 12.3 g $H_2$ reacts?

• Balanced equation: $2\ H_2\ (g) + 1\ O_2\ (g) \rightarrow 2\ H_2O\ (g)$

• Steps:

  1. Convert 12.3 g $H_2$ to moles: $\text{moles } H_2 = \frac{12.3\ g}{2.016\ g/mol}$

  2. Use the mole ratio from the equation: $2\ H_2 : 2\ H_2O$ (1:1 ratio)

  3. Convert moles of $H_2O$ to grams: $\text{grams } H_2O = \text{moles } H_2O \times 18.02\ g/mol$

Practice Problems

Oxidation of Chromium

The oxidation of chromium solid is represented by the following equation:

• $4\ Cr\ (s) + 3\ O_2\ (g) \rightarrow 2\ Cr_2O_3\ (s)$

• Practice: How many moles of chromium(III) oxide are produced when 34.69 g Cr reacts with excess oxygen gas?

Reaction of Potassium Chlorate and Sucrose

The reaction is given below:

• $8\ KClO_3 + C_{12}H_{22}O_{11} \rightarrow 8\ KCl + 12\ CO_2 + 11\ H_2O$

• Practice: If $2.33 \times 10^4$ formula units of potassium chlorate are reacted, how many grams of carbon dioxide will be produced?

Density and Volume Calculations

Practice: If the density of ethanol, $CH_3CH_2OH$, is 0.789 g/mL, how many milliliters of ethanol are needed to produce 4.8 g of $H_2O$ in the following reaction?

• $CH_3CH_2OH\ (l) + 3\ O_2\ (g) \rightarrow 3\ H_2O\ (l) + 2\ CO_2\ (g)$

Summary Table: Stoichiometric Steps

Step	Description	Key Formula
1	Convert given mass/units to moles	$\text{moles} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}}$
2	Use mole ratio from balanced equation	$\text{moles of unknown} = \text{moles of given} \times \frac{\text{coefficient of unknown}}{\text{coefficient of given}}$
3	Convert moles of unknown to desired units	$\text{mass} = \text{moles} \times \text{molar mass}$

Additional info:

• Practice problems reinforce the application of stoichiometric steps in real chemical reactions.

• Understanding mole-to-mole relationships is essential for predicting product yields and reactant requirements.