Key Terms – Chapter 01

Accuracy How closely a measured value agrees with the correct value.

Calorie Defined as exactly 4.184 joules. Originally defined as the amount of heat required to raise the temperature of one gram of water from 14.5°C to 15.5°C.

Chemical change A change in which one or more new substances are formed.

Chemical property See Properties.

Compound A substance composed of two or more elements in fixed proportions. Compounds can be decomposed into their constituent elements.

Density Mass per unit volume, D  = m/V.

Element A substance that cannot be decomposed into simpler substances by chemical means.

Endothermic Describes processes that absorb heat energy.

Energy The capacity to do work or transfer heat.

Exothermic Describes processes that release heat energy.

Extensive property A property that depends on the amount of material in a sample.

Heat A form of energy that flows between two samples of matter because of their difference in temperature.

Heat Capacity The amount of heat required to raise the temperature of a body (of whatever mass) one degree Celsius.

Heterogeneous mixture A mixture that does not have uniform composition and properties throughout.

Homogeneous mixture A mixture that has uniform composition and properties throughout.

Intensive property A property that is independent of the amount of material in a sample.

Joule A unit of energy in the SI system. One joule is 1 kg.m2/s2, which is also 0.2390 cal.

Kinetic Energy Energy that matter possesses by virtue of its motion.

Law of Conservation of Energy Energy cannot be created or destroyed in a chemical reaction or in a physical change; it may be changed from one form to another.

Law of Conservation of Matter No detectable change occurs in the total quantity of matter during a chemical reaction or during a physical change. 

Law of Conservation of Matter and Energy The combined amount of matter and energy available in the universe is fixed.

Law of Constant Composition See Law of Definite Proportions.

Law of Definite Proportions Different samples of any pure compound contain the same elements in the same proportions by mass; also known as the Law of Constant Composition.

Mass A measure of the amount of matter in an object. Mass is usually measured in grams or kilograms.

Matter Anything that has mass and occupies space.

Mixture A sample of matter composed of variable amounts of two or more substances, each of which retains its identity and properties.

Physical change A change in which a substance changes from one physical state to another, but no substances with different compositions are formed.

Physical property See Properties.

Potential energy Energy that matter possesses by virtue of its position, condition, or composition.

Precision How closely repeated measurements of the same quantity agree with one another.

Properties Characteristics that describe samples of matter. Chemical properties are exhibited as matter undergoes chemical changes. Physical properties are exhibited by matter with no changes in chemical composition.

Scientific (natural) law A general statement based on the observed behavior of matter, to which no exceptions are known.

Significant figures Digits that indicate the precision of measurements— digits of a measured number that have uncertainty only in the last digit.

Specific gravity The ratio of the density of a substance to the density of water at the same temperature.

Specific heat The amount of heat required to raise the temperature of one gram of a substance one degree Celsius.

Substance Any kind of matter all specimens of which have the same chemical composition and physical properties.

Symbol (of an element) A letter or group of letters that represents (identifies) an element.

Temperature A measure of the intensity of heat, that is, the hotness or coldness of a sample or object.

Unit factor A factor in which the numerator and denominator are expressed in different units but represent the same or equivalent amounts. Multiplying by a unit factor is the same as multiplying by one.

Weight A measure of the gravitational attraction of the earth for a body.