Measurement of Temperature
Understanding Thermal Energy, Scales, and Interconversions.
Before we can study the Gas Laws (Boyle's, Charles's, etc.), we must understand the fundamental parameters that define a gas: Pressure, Volume, and Temperature. Let's explore what temperature actually represents and how we measure it.
1. What is Temperature?
Macroscopically, temperature is a measure of the "degree of hotness or coldness" of a body, which determines the direction of heat flow. Heat always flows from a body at a higher temperature to one at a lower temperature.
Microscopically (Kinetic Molecular Theory), temperature is a direct measure of the average kinetic energy of the particles in a substance.
2. The Three Temperature Scales
| Scale | Freezing Point of Water | Boiling Point of Water | Number of Divisions |
|---|---|---|---|
| Celsius ($^\circ C$) | $0^\circ C$ | $100^\circ C$ | 100 |
| Fahrenheit ($^\circ F$) | $32^\circ F$ | $212^\circ F$ | 180 |
| Kelvin ($K$) (SI Unit) |
$273.15 \text{ } K$ | $373.15 \text{ } K$ | 100 |
3. Interconversion Formulas
To convert from one scale to another, you can memorize specific formulas or use one universal relation.
Celsius ↔ Kelvin
(For most numericals, using 273 is sufficient)
Celsius ↔ Fahrenheit
The Universal Conversion Formula
Just equate the two parts you need and solve!
4. The Concept of Absolute Zero
Why do we need the Kelvin scale? Gas laws (like Charles's Law) require temperature to be directly proportional to volume. If temperature is $0^\circ C$ or negative, the math breaks down.
- Absolute Zero ($0 \text{ } K$ or $-273.15^\circ C$): This is the theoretical lowest possible temperature in the universe.
- At this temperature, the kinetic energy of ideal gas molecules becomes exactly zero, and molecular motion theoretically ceases.
- Because you cannot have less than zero kinetic energy, the Kelvin scale has no negative numbers.
Knowledge Check
Test your ability to convert temperature scales
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