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Mark S. Cracolice
Edward I. Peters
www.cengage.com/chemistry/cracolice
Chemistry is the study of matter, its
transformations, and the energy
changes that accompany those
transformations.
Mark S. Cracolice • The University of Montana
Mark S. Cracolice
Edward I. Peters
www.cengage.com/chemistry/cracolice
Chapter 2
Matter and Energy
Mark S. Cracolice • The University of Montana
2.1 Matter, Mass and Weight
Matter
Anything that has mass and takes up space is called matter.
Mass
Mass of an object is determined by its resistance in motion and
is a measure of the quantity of matter.
Weight
Weight is the force of gravity. The weight of an object is
proportional to the mass:
Weight = mass x acceleration of gravity
2.2 States of Matter
States of Matter: Gas, Liquid, Solid
The air you breathe is a gas.
The water you drink is a liquid.
The food you eat is a solid.
2.2 States of Matter: Gas
• Gas is a fluid form of matter. It fills any container it
occupies.
• At low pressure ( p < 1 atm) particles are far apart
compared with their dimension. Particles are independent
of one another. Attraction among particles is important
only at high pressure (p > 30 atm).
• Particles are moving in random fashion. At room
temperature the speed of carbon dioxide molecule is
around 400 m/s. The speed at which particles move is
faster at higher temperatures and slower at lower
temperatures.
2.2 States of Matter: Solid
• Solid is a rigid form of matter. Shape and volume are
constant.
• Particles are close together. Particle interaction is
very strong.
• Particles rotate and vibrate in fixed positions relative
to one another.
2.2 States of Matter: Liquid
• Liquid is a fluid form of matter.
• Liquid has a constant volume but takes the shape of
the part of the container it occupies.
• Particles move freely among themselves, but clump
together.
2.2 States of Matter
2.3 Properties and Changes
• A physical property of a substance is a
characteristic that we observe or measure without
changing the identity of the substance.
• A chemical property of a substance is a
characteristic that we observe or measure only by
changing the identity of the substance.
2.3 Properties and Changes
Physical Changes
Changes in physical form of matter without changes
in chemical identity. No new substance formed
Examples
Fusion, solidification
Vaporization, condensation
Sublimation, deposition
2.3 Properties and Changes
In a Physical Change, the Molecules are Unchanged:
2.3 Properties and Changes
Chemical Changes
Chemical identity of a substance is destroyed
A new substance is formed
Example
Water decomposes to hydrogen and oxygen gases
when subjected to an electrical current
Properties and Changes
In a Chemical Change, the Molecules Change:
2.3 Properties and Changes
Chemical Properties
The types of chemical change a substance
is able to participate in.
Example
A chemical property of water is that it can be
decomposed to its elements when subjected to an
electrical current.
2.3 Properties and Changes
Chemical
Physical
Chemical identity of a
substance is destroyed
New form of same
substance
New substances formed
No new substances
formed
Types of chemical
changes possible
Description as detected
by the senses
Changes
Properties
Measurable properties
2.4 Substances and Mixtures
Pure Substance
A sample consisting of only one kind of matter,
either compound or element;
made up entirely of one kind of particle.
Unique set of physical and chemical properties.
Cannot be separated into parts by a physical change.
2.4 Substances and Mixtures
Mixture
A sample of matter that consists of two or more
substances.
Physical and chemical properties of a mixture vary with
different relative amounts of the parts.
Can be separated into parts via physical processes.
2.4 Substances and Mixtures
Pure water has a constant boiling
point—a physical property.
The boiling point of a mixture
(solution) changes as the
composition of the mixture
changes.
2.4 Substances and Mixtures
You cannot distinguish a pure substance from a mixture of
uniform appearance by observation alone at the macroscopic
level.
2.4 Substances and Mixtures
Homogeneous
A sample that has uniform
appearance and composition throughout.
Solution
A homogeneous mixture of two or more components.
Heterogeneous
A sample with different phases, usually visible.
Substances and Mixtures
Homogeneous Matter may be Either a Pure Substance or a
Mixture:
2.5 Separation of Mixtures
Most natural substances are mixtures.
Separation processes are an important part of
chemistry.
Nitrogen and oxygen are separated from the mixture
called air.
Pure water is separated from the mixture called natural
water.
2.5 Separation of Mixtures
A Physical Property, Magnetism, Allows a Mixture of Iron and
Sulfur to be Separated:
2.5 Separation of Mixtures
Distillation
Separation of the parts of a mixture by heating a liquid solution
until one component boils, changing into the gaseous state.
The pure substance in the gaseous state is then
collected and cooled into the liquid state.
Boiling is a physical change.
Distillation allows components in a homogeneous mixture
to be separated into one or more pure substances.
2.5 Separation of Mixtures
Laboratory Distillation Apparatus:
2.5 Separation of Mixtures
Filtration
Separation of the components of a mixture by physical means by
using a porous medium, such as filter paper, to separate
components based upon relative particles sizes.
Filtration is based on the physical properties of a mixture:
The particle sizes of a component to be separated
must be significantly larger or smaller than the
pore size of the filtration medium.
2.5 Separation of Mixtures
Gravity Filtration
2.6 Elements and Compounds
Element
Pure substance that cannot be decomposed into other
pure substances by ordinary chemical means.
Atom
Smallest particle of an element that can combine with
atoms of other elements to form compounds.
Compound
Pure substance that can be broken down into two or
more other pure substances by a chemical change.
2.6 Elements and Compounds
Mixtures are separated into pure substances by physical means;
compounds are separated into pure substances by chemical
changes.
2.6 Elements and Compounds
Elements
At least 88 elements occur in nature.
Examples: copper, sulfur, gold, silver
11 elements occur in nature at room temperature as
gases;
2 occur as liquids (mercury and bromine);
the others occur as solids.
2.6 Elements and Compounds
Major Elements of the Human Body
Element
Hydrogen
Oxygen
Carbon
Nitrogen
Percentage Composition by Number of Atoms
63.0
25.5
9.45
1.35
These four elements make up 99.3% of the atoms in your body.
2.6 Elements and Compounds
Elemental Symbols
The first letter of the name of the element,
written in uppercase, is often its symbol.
Examples: Hydrogen, H; Oxygen, O; Carbon, C
If more than one element begins with the same letter,
a second lowercase letter is added.
Examples: Helium, He; Chlorine, Cl
2.6 Elements and Compounds
Chemical Formulas
Symbolic representations of the particles of a pure substance.
A combination of the symbols of all the elements in a substance.
The formula of most elements is the same as the symbol of the
element, e.g., helium, He; sodium, Na.
Other elements exists in nature as molecules and their formulas
indicate the number of atoms of the element in the molecule,
e.g., hydrogen, H2; oxygen, O2.
2.6 Elements and Compounds
Formula Unit
Molecule or simplest ratio of particles for non-molecular
species.
Ammonia molecules have the formula NH3:
1 atom of nitrogen and 3 atoms of hydrogen.
Magnesium chloride has the formula unit MgCl2.
2.6 Elements and Compounds
Law of Constant Composition
Any compound is always made up of elements in
the same proportion by mass.
No matter its source, water (H2O) is
11.1 parts hydrogen per 88.9 parts oxygen.
2.6 Elements and Compounds
The Properties of a Compound are Different from the
Properties of the Elements that Make Up the
Compound:
Water, H2O
Liquid at 25°C, melts at 0°C, boils at 100°C
Hydrogen, H2
Gas at 25°C, melts at –259°C, boils at –253°C
Oxygen, O2
Gas at 25°C, melts at –219°C, boils at –183°C
2.6 Elements and Compounds
Summary of the Classification System for Matter:
2.7 Electrical Character of Matter
Matter has electrical properties. There are only two
types of electrical charge, positive and negative.
Two objects having the same charge, both positive or
both negative, repel each other.
Two objects having different charges, one positive
and one negative, attract each other.
2.7 Electrical Character of Matter
2.7 Electrical Character of Matter
2.7 Electrical Character of Matter
Electrostatic Attraction and Repulsion
2.8 Chemical Change
Chemical Equation
A symbolic representation of chemical change, with the formulas
of the beginning substances to the left of an arrow that points
to the formulas of the substances formed.
Reactant: Original substance
Product: Substance formed as a result of chemical change
2 H 2O
Reactant

2 H2 + O2
Products
2.8 Chemical Change
Exothermic Reaction
A chemical change that releases energy to its
surroundings.
Example:
Burning charcoal
C + O2

CO2 + energy
2.8 Chemical Change
Endothermic Reaction
A chemical change that absorbs energy from its
surroundings.
Example:
Decomposition of water to its elements
2 H2O + energy

2 H2 + O2
2.9 Conservation Laws
Law of Conservation of Mass
In any ordinary chemical change,
total mass of reactants = total mass of products
Number of atoms of each element is the same before
and after the reaction.
2.9 Conservation Laws
Law of Conservation of Charge
In any ordinary chemical change,
total charge of reactants = total charge of products
Electric charge is unchanged in the reaction
• NaCl

Na+ +
Cl-
2.9 Conservation Laws
Law of Conservation of Energy
Energy is the capacity to do work or supply heat. A system
can exchange its energy with its surrounding in two forms:
heat and work.
Heat is the transfer of energy as a result of a difference in
temperature. Work is done when an object is moved against
an opposing force. Heat and work are equivalent ways of
changing the energy of a system.
Energy of an isolated system is conserved; it is neither created
nor destroyed.
2.9 Conservation Laws
Law of Conservation of Energy
The form (as heat or as work) in which energy is released
depends on how the reaction takes place.
For example in normal condition the reaction between hydrogen
and oxygen releases heat
2 H2 + O2  2 H2O + energy as heat
But this same reaction in a fuel cell can generate electricity and
produce work
2 H2 + O2  2 H2O + energy as work
Homework
• You need to have a notebook for homework.
• Homework notebook will be checked on days of the exam.
• Homework for chapter 2:
23, 29, 39, 43, 51, 53, 55, 66, 71, 72, 73