Physical and Chemical Properties of Matter

This page delves deeper into the properties of matter, distinguishing between physical and chemical properties. Understanding these properties is crucial for solving stoichiometry problems and answers.

Definition: Physical properties are observed without changing the identity and composition of the substance.

Examples of physical properties include color, odor, density, melting point, boiling point, and hardness.

Definition: Chemical properties describe how a substance may change or react to form other substances.

Chemical properties include flammability, corrosiveness, and reactivity with acids.

The page also introduces intensive and extensive properties:

• Intensive properties are independent of the amount of substance present (e.g., temperature, melting point)
• Extensive properties depend on the amount of sample (e.g., mass, volume)

Highlight: Understanding the difference between physical and chemical changes is essential for stoichiometric calculations.

The text explains dissociation and introduces the concept of electrolytes, which is important for understanding reactions in aqueous solutions.

Vocabulary: An electrolyte dissociates into ions when dissolved in water.

This information is crucial for performing stoichiometric calculations with chemical formulas and equations involving ionic compounds.

Chemical Equations and Reactions

This page introduces the basics of chemical equations and different types of chemical reactions, which are fundamental to stoichiometric calculations.

Definition: A subscript in a chemical formula indicates the number of atoms of an element in a molecule or formula unit.

Definition: A coefficient in a chemical equation indicates the number of molecules or formula units of a substance.

The text covers three main types of chemical reactions:

1. Combination reaction: A + B → C
2. Decomposition reaction: C → A + B
3. Combustion reaction: Hydrocarbons reacting with oxygen in air

Highlight: Understanding these reaction types is crucial for balancing equations and performing stoichiometric calculations.

The page also introduces the concepts of formula weight and molecular weight:

• Formula Weight: Sum of atomic weights for atoms in a formula unit
• Molecular Weight: Sum of atomic weights in a molecule

Example: For AB₂, if A has an atomic weight of 1 amu and B has an atomic weight of 2 amu, the formula weight would be 1 + (2 × 2) = 5 amu.

Lastly, the text mentions percent composition, which is the percentage of mass of a compound contributed by each element. This concept is essential for solving various stoichiometry problems and answers.