Temperature is an indication of the presence or absence of heat (thermal energy).  The average temperature at the equator is higher than the average temperature of the Arctic due to the presence of more heat (thermal energy).  A plate of hot food has a higher temperature than a glass of ice water again due to the presence of more heat in the plate.

If a one touches a finger to a plate of hot food, the finger will feel warm or hot.  This is because heat (thermal energy) is moving from the hot plate to the finger.  Likewise touching a glass of ice water provides the sensation of cool or cold as heat is transferred from the hand to the glass.  Heat will move from the hotter object (more heat, more thermal energy) to the cooler object (less heat, less thermal energy).

These observations will be needed when we discuss the sections on Interactions and Reactions.  The majority of chemical interactions and reactions involve heat.  If heat is released when chemicals interact or react, the temperature of the area around the process increases.  This process is called exergonic.  If heat is absorbed when chemicals interact or react, the temperature around the process decreases. This process is called endergonic.

Temperature is measured using a thermometer (see Wikipedia for the historical development of thermometers) and can be measured in units of Fahrenheit (F), Celsius (C), Kelvin (K)1. As was noted in the Math Skills section, Fahrenheit is an English unit and can be abbreviated with an F, Celsius is a derived unit abbreviated with a C, and Kelvin is an SI unit abbreviated with a K.

Traditional thermometers contain a column of Mercury in a sealed tube with a scale marked on the tube. The Mercury will expand in the presence of more heat and contract when there is less heat.  See Wikipedia for more information regarding Mercury thermometers.

Fahrenheit and Celsius temperature scales are based on the freezing point and the boiling point of water.  Fahrenheit uses 32 degrees for the freezing point of water and 212 degrees for the boiling point of water.  Thus there are 180 degrees between the two points.  Celsius uses 0 degrees for the freezing point of water and 100 degrees for the boiling point of water.  There are 100 degrees between the two points. Each Fahrenheit degree is 1.8 times larger than each Celsius degree.  This is the ratio of between 180 degrees Fahrenheit and 100 degrees Celsius.  This difference in the two scales complicates conversion between them.

Equations for converting between Faharenheit and Celsius are:

F = 9 / 5 C + 32
C = 5 / 9 (F – 32)

The ratio 9/5 or 5/9 is the reduction of the ratio between the two scales (180/100 or 100/180).  The 32 is the difference between the freezing points on the two scales.

The unit of degree is represented by a superscript o.  Seventy degrees could also be written as 70o.

See the following links for more information and to access Conversion calculators.

Conversion Calculator
Explanation and Conversion Calculator

There are two other terms the student may encounter in a discussion of temperature.

Ambient temperature which refers to the temperature of the surroundings.
Room temperature refers to the temperature in a temperature controlled building.

These two temperatures are dependent on the circumstance.  The ambient temperature in the Rocky Mountains is different than the ambient temperature of the plains.  Likewise room temperature depends on the amount of heating or cooling capacity of a building or room and the comfort level of the occupants.  It is possible the ambient and room temperature would be the same.

It will be shown in later sections that some physical properties depend on the amount of heat present and hence on the temperature.  Chemical properties are also dependent on the presence or absent of heat.  So it is necessary to include the temperature when reporting information about these properties.

See Wikipedia for a more in-depth discussion of temperature.

The following YouTube videos will help the student understand the difference between heat (thermal energy) and temperature.  Heat and Temperature Introduction and Heat and Temperature

The Heat and Temperature video emphasizes the importance of the number of entities (atoms, ions, molecules) when discussing thermal energy.  The number of entities will be important in other disscusions of chemistry.  See the page Avogadro’s number and moles .

1Kelvin temperature is based on the principle there is a point where no heat exists which is referred to as absolute zero on the Kelvin scale.  This temperature scale is used primarily by scientists.