Chapter 1 Notes - Beckford

Chapter 1 Notes
Dr. Floyd Beckford

FOUNDATIONS OF CHEMISTRY

Matter:

Matter is anything that has mass and takes up space. Examples include a pen, a book and air. An easily observed property of matter is its physical state. Matter can exist as three distinct states or phases.
1. Solid: - A solid has the characteristic of definite shape with closely compacted particles. This means that a solid will have a definite volume and that volume does not vary much when conditions are changed.
· There is very strong interaction between the particles of a solid. This makes solids very hard to compress.

2. Liquid: - A liquid has the characteristic of having its particles move freely while retaining a definite volume. The mobility of the particles gives a liquid its fluidity and causes it to take the shape of its container.
· The interactions of the liquid particles are not as strong as in solids so liquids are more compressible than solids but are still not very compressible.

2. Gas: - Gases have the characteristic of having no fixed shape, with its particles moving independently of each other. A gas presses continuously and in all directions upon the wall of the vessel in which it is contained. Because of this quality the gas will completely fill the vessel.
· The particles of gas are independent of each other. They are very far apart and this makes gases very compressible

Chemical and Physical properties

Matter can be recognized by its various characteristics or properties. There are two broadly defined categories: chemical and physical properties.
· Chemical properties are those that relate to the ability of a substance to form new substances. Chemical properties are therefore those that involve chemical changes as in a chemical reaction. Examples of chemical properties include
(i) burning in air (combustion)
(ii) reaction with water
(iii) reaction with acids or bases

· Physical properties are inherent characteristics of a substance that may be determined without altering the composition of that substance; they are associated with its physical existence. Examples include
(i) color
(ii) solubility
(iii) melting point
(iv) electrical and thermal conductivity

Changes in Matter
Matter can undergo two types of changes, physical and chemical.
Physical changes involve mainly changes in physical properties (size, shape, density etc.) or changes of state (solid --> liquid etc.) without an accompanying change in composition. No new substances are formed. Examples, melting, heating a metal wire color changes, etc.
In a chemical change, substances are formed that have entirely different properties and composition from the original material. Chemical changes are associated with chemical properties.

	Mercuric oxide --->   Mercury  +    Oxygen
	100g                92.6 g           7.40 g

Looking at the reaction above we have 100 g of reactant and 100 g of product. This can be expressed as the Law of Conservation of Matter, which states that there is no observable change in the quantity of matter during a chemical reaction or a physical change.

Mixtures and Compounds
Most of the matter we find in nature is a mixture of two or more pure substances. Two kinds of mixtures exist;
1. Heterogeneous – The components of heterogeneous mixtures are distributed unevenly and they are not combined in any set amount relative to each other e.g. salt and sand.
2. Homogeneous – Homogeneous mixtures are also called solutions. These mixtures have components that are uniformly distributed.
In any mixture the composition can be varied and each component retains its own properties.

A compound is a substance that can be decomposed by chemical means into simpler substances. Another popular definition is a compound is a pure substance consisting of two or more elements in a fixed ratio. This observation has led to the statement of the Law of Definite Proportions (or Law of Constant Composition): Different samples of any pure compound contain the same elements in the same proportion by mass.

ENERGY

Energy is defined as the capacity or ability of matter to do work. Energy can be classified into two principal types:
1. kinetic energy is energy possessed by a moving body e.g. a moving car
2. potential energy is stored energy or energy an object possesses due to its relative position e.g. gasoline. Gasoline represents a source of stored chemical energy that can be released during combustion in an engine.

Consider the reaction of magnesium and oxygen to form magnesium oxide.

2Mg + O₂ ---> 2MgO + { heat + light} Chemical reactions, such as the one above, ordinarily occur with some sort of energy change. A reaction that requires an input of energy is said to be endothermic and a reaction that releases energy is said to be exothermic.

Regardless of the energy change, it has been shown that all of the energy at the beginning of the reaction appears in some form at the end. This is a statement of the Law of Conservation of Energy: Energy cannot be created or destroyed in a chemical reaction or a chemical change. It can only be converted from one form to another.