Chapter 7: Chemical Reactions and Quantities – Study Notes

Chapter 7: Chemical Reactions and Quantities

Introduction to Chemical Reactions and Quantities

This chapter explores the fundamental concepts of chemical reactions, focusing on how substances interact, transform, and are quantified in chemical processes. Understanding these principles is essential for analyzing reactions in both laboratory and real-world contexts, such as physiology and industry.

Chemical Equations for Chemical Reactions

What is a Chemical Reaction?

• Chemical change occurs when a substance is converted into one or more new substances with different formulas and properties.

• These changes are represented by chemical equations, which show the reactants (starting materials) and products (new substances formed).

Evidence of Chemical Reactions

• Change in color (e.g., iron rusting)

• Formation of a gas (bubbles)

• Formation of a solid (precipitate)

• Heat or light produced or absorbed

Example: Iron nails change color when they react with oxygen to form rust (Fe2O3).

Writing and Interpreting Chemical Equations

• Reactants are written on the left; products on the right.

• An arrow (→) separates reactants from products.

• Plus signs (+) separate multiple reactants or products.

• Physical states are indicated: (s) solid, (l) liquid, (g) gas, (aq) aqueous.

• The delta symbol (Δ) indicates heat is applied.

General format: reactant + reactant → product + product

Balancing Chemical Equations

To satisfy the law of conservation of mass, chemical equations must be balanced so that the number of atoms of each element is the same on both sides.

1. Write the correct formulas for all reactants and products.

2. Count the number of atoms of each element on both sides.

3. Add coefficients to balance the atoms for each element.

4. Check that all coefficients are in the lowest possible ratio.

Example: Balancing the formation of aluminum sulfide:

• Unbalanced: Al(s) + S(s) → Al2S3(s)

• Balanced: 2Al(s) + 3S(s) → Al2S3(s)

Key Terms

• Reactant: A starting substance in a chemical reaction.

• Product: A substance formed as a result of a chemical reaction.

• Coefficient: A number placed in front of a formula to balance the equation.

• Subscript: A small number in a chemical formula indicating the number of atoms of an element.

Applications

• Balancing equations is essential for calculating the quantities of reactants and products in laboratory and industrial processes.

• Understanding chemical changes is crucial in fields such as physiology, where metabolic reactions are central to health and disease management.

• Understanding chemical changes is crucial in fields such as physiology, where metabolic reactions are central to health and disease management.

Example Table: Symbols Used in Chemical Equations

Symbol	Meaning
+	Separates two or more formulas
→	Reacts to form products
(s)	Solid
(l)	Liquid
(g)	Gas
(aq)	Aqueous (dissolved in water)
Δ	Heat is applied

Additional info: Later sections of this chapter will cover types of chemical reactions, stoichiometry, limiting reactants, and energy changes in reactions.