Temperature as a Measure of Kinetic Energy
- Have you ever wondered what makes a cup of hot coffee feel warm in your hands? The answer lies in the invisible dance of molecules.
- These particles are moving, colliding, and transferring energy, creating the heat you feel.
- But how can we quantify this energy?
This is where temperature comes in.
Definition
Temperature
Temperature is a direct measure of the average kinetic energy of the particles in a substance.
The Kelvin Scale: Directly Proportional to Kinetic Energy
- In science, the Kelvin scale is the standard unit of temperature because it directly correlates with the average kinetic energy of particles.
- On this scale, absolute zero (0 K) represents the point where particles have no kinetic energy: they are completely motionless (in theory).
- This makes the Kelvin scale an "absolute" temperature scale, ideal for scientific calculations.
The relationship between temperature in Kelvin and the average kinetic energy ($E_k$) of particles is:
$$
E_k \propto T(K)
$$
This proportionality means that if the Kelvin temperature of a substance doubles, the average kinetic energy of its particles also doubles.Note
- Absolute zero (0 K or -273.15°C) is a theoretical temperature at which all particle motion stops.
- While unattainable in practice, it serves as a crucial reference point for understanding temperature.
Relationship Between Kelvin and Celsius
- The Kelvin and Celsius scales are closely related, differing only in their starting points.
- While the Celsius scale is based on the freezing (0°C) and boiling points (100°C) of water, the Kelvin scale starts at absolute zero.
The conversion formula is:
$$
T(K) = T(°C) + 273.15
$$
- Water freezes at 0°C, which is equivalent to $0 + 273.15 = 273.15 \, \text{K}$.
- Water boils at 100°C, which is $100 + 273.15 = 373.15 \, \text{K}$.
Convert 25°C to Kelvin:
$$
T(K) = 25 + 273.15 = 298.15 \, \text{K}
$$
Do not confuse the size of a Kelvin unit with a Celsius degree. Both scales have the same incremental size (1 K = 1°C), but their starting points differ.
Observable Changes During Temperature Changes
- When the temperature of a substance changes, the kinetic energy of its particles changes as well.
- This can lead to several observable effects:
Expansion or Contraction of Matter
- As particles gain kinetic energy, they move more vigorously and occupy more space, causing expansion.
- Conversely, when particles lose energy, they slow down and take up less space, leading to contraction.
