General Chemistry

Dr. Nguyen Viet Hung

Chapter 1.Matter and Energy Objectives

Use the basic vocabulary of matter and energy

Distinguish between chemical and physical properties; and between chemical and physical changes

Recognize various forms of matter Understand the concepts: mixture,

substance, compounds, element, molecule and atoms

Matter: Matter is anything that has mass and

occupies space Mass is a measure of the quantity of

matter in a sample of any material

Mass and weight

Difference between mass and weight 1) Mass is a measurement of the amount

of matter something contains, while Weight is the measurement of the pull of gravity on an object.

2) The Mass of an object doesn't change when an object's location changes. Weight, on the otherhand does change with location.

Energy Energy is defined as the capacity

to do work or transfer heat Many forms of energy, including

light energy, electrical energy and heat energy.

Energy can be classified into 2 principle types: kinetic energy and potential energy

Potential energy

CoalRock atop a mountain

Example

Which of the following illustrate the concept of potential energy and which ilustrate kinetic energy?(a) water stored in a water tower (b) a rubber band stretched (c) a comet moving through space (d) the roof of a house

Exothermic and endothermic processes

Exothermic Endothermic

The law of conservation of matter: there is no observable change in the quantity of matter during a chemical reaction or during a physical change

The law of conservation of energy: energy cannot be created or destroyed. I can only be converted from one form to another

The combined amount of matter and energy in the universe is fixed

The relationship between energy and matter:

E= mc2 (c is the speed of light)

States of matter Solid: substances are rigid and have

definite shapes Liquid: flows and assume the shape of

its container Gases are much less dense than

liquids and solids, can be compressed easily

Iodine Bromine Chlorine

Chemical and Physical properties Chemical properties are exhibited by

matter as it undergoes changes in composition

All substances also exhibit physical properties that can be observed in the absence of any change in composition Color, density, hardness, melting point,

boiling point and electrical and thermal conductivities

Extensive and intensive properties

Extensive: The volume and mass of a sample depend on and directly propotional to, the amount of matter in that sample

Intensive: the color and the melting point are the same for a small sample and for a large one

Chemical and Physical changes

In any physical change (no change in chemical composition) (3 states of matter)

In any chemical change One or more substances are used up One or more new substances are

formed, Energy is absorbed or released

Physical changes that occur among the three states of matter

Gas

Solid Liquid

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Melting

Freezing

Condensation

Evaporation

Example Which of the following are chemical

properties, which are physical properties?(a) Striking a match causes it to burst into flames. (b) A particular type of steel is very hard and consists of 95% iron, 4% carbon, and 1% other elements. (d) Fine steel wool burns in air

Example

Label each of the as either a physical process or a chemical process:(a) rusting of an iron bridge, (b) melting of ice; (c) burning of a wooden stick; (d) digestion of a baked potato

Atoms and Elements

All of the different substances are composed of only around 100 elements

Each atom of a specific element is chemically identical to every other atom and contains the same number of protons in its nucleus

The number of protons in the nucleus of each atoms of an element is the atomic number of the element

Mixtures, substances, compounds and elements

Mixtures: combinations of two or more pure substances in which each substance retains its own composition and properties (can be seperated by physical means)

Substance (pure substance): cannot be further broken down or purified by physical means.

A compound is a substance that can be decomposed by chemical means into simpler substances, always in the same ratio by mass (H2O through electrolysis form H2 and O2)

Electrolysis of water

An element is a substance that cannot be decomposed into simpler substances by chemical changes (H, O)

Atoms: the smallest particle of an element that maintains its chemical identities through all chemical and physical changes

Atoms consist principally of three fundermental particles: electrons, protons and neutrons

Scheme for classification of matter

Matter

MixtureVariable composition

Can be seperated

Pure substancesFixed composition

Cannot be seperated (phys)But by chem. method

Homegeneous mixturesSame composition

Components indistinguishable

Heterogeneous mixturesNot same composition

DistinguishableCompounds

Can be decomposed

ElementsCannot be

Physical changes

Chemical changes

A molecule is the smallest particle of an element or compound that can have a stable independent existence. In nearly all molecules, two or more atoms are bonded together

An ion is an atom or group of atoms that carries an electric charge. Ions that posses a positive charge are called cations. Those carrying a negative charge are called anions.

Symbols of the most common elements

the only metal that is a liquidAt room temperature Sulfur is solid at roomtemperature

Abundance of elements in the Earth’s crust

Example Classify each of the following as

element, a compound, or a mixture (Explain) A soft drink, seawater, air, chicken

noodle soup, table salt, copper wire, popcorn, ice cream

Gasoline, tap water, calcium carbonate, ink from a ball point pen, toothpaste, aluminum foil