Chemical Reactions and Stoichiometry: Study Notes for CHY 102

Chemical Reactions and Stoichiometry

Chapter Outline

• Balancing Chemical Equations

• Solutions and Solubility

• Precipitation Reactions

• Acid-Base Reactions

• Oxidation-Reduction Reactions

• Stoichiometry: How Much is Produced?

• Limiting Reactant, Theoretical Yield, and Percent Yield

• Concentration and Solution Stoichiometry

The Chemistry of Cuisine

Chemical Reactions in Cooking

Cooking food involves a variety of chemical reactions that change its color, flavor, and texture. These reactions are central to the transformation of raw ingredients into edible dishes.

• Maillard Reaction: Heating food containing proteins and sugars produces flavorful aromatic compounds, responsible for browning and taste in many recipes.

• Myoglobin Conversion: Heat causes the myoglobin protein in meat to convert to metmyoglobin, changing color from red to brown due to electron loss.

• Baking Powder Reaction: Baking powder contains sodium bicarbonate (a base) and an acid. When wet, they react to produce carbon dioxide, which expands and causes cakes to rise.

• Odor Changes: As food decays, volatile amines are produced (fishy smell). Reacting with certain compounds can neutralize these odors.

Example: The rising of cakes is due to the production of carbon dioxide gas from the reaction of baking powder ingredients.

Writing and Balancing Chemical Equations

Fundamentals of Chemical Equations

A chemical reaction is a process in which one or more substances are converted into new substances. Chemical equations represent these reactions using formulas and symbols.

• Reactants: Substances present before the reaction.

• Products: Substances formed as a result of the reaction.

• State Symbols: Indicate the physical state of each substance.

Abbreviation	State
(g)	Gas
(l)	Liquid
(s)	Solid
(aq)	Aqueous (water solution)

Example Equation:

$\mathrm{CH}_4(g) + \mathrm{O}_2(g) \rightarrow \mathrm{CO}_2(g) + \mathrm{H}_2O(g)$

Balancing Chemical Equations

A balanced chemical equation has equal numbers of each type of atom on both sides, satisfying the law of conservation of mass.

• Write the molecular formulas for all reactants and products.

• Balance atoms in more complex substances first.

• Balance pure elements last.

• Check the balance of all atoms.

Example:

Unbalanced: $\mathrm{CH}_4(g) + \mathrm{O}_2(g) \rightarrow \mathrm{CO}_2(g) + \mathrm{H}_2O(g)$

Balanced: $\mathrm{CH}_4(g) + 2\mathrm{O}_2(g) \rightarrow \mathrm{CO}_2(g) + 2\mathrm{H}_2O(g)$

Stoichiometric Coefficients

Coefficients are used to balance equations and indicate the number of molecules or moles involved.

Example: Balancing the combustion of butane:

$\mathrm{C}_4\mathrm{H}_{10}(g) + \frac{13}{2}\mathrm{O}_2(g) \rightarrow 5\mathrm{H}_2O(g) + 4\mathrm{CO}_2(g)$

Atom	# Atoms (reactant)	# Atoms (product)
C	4	4
H	10	10
O	2 × 13/2 = 13	13

Sometimes, fractional coefficients are used and then multiplied to obtain whole numbers.

*Additional info: The notes cover foundational concepts in chemical reactions, balancing equations, and stoichiometry, which are essential for General Chemistry students. Further sections (not shown in these images) likely expand on solution chemistry, precipitation, acid-base, and redox reactions, as indicated in the chapter outline.*