Kelvin

Definition

Kelvin is the base unit of temperature in the International System of Units (SI). It is named after the physicist William Thomson, also known as Lord Kelvin, who was the first to propose an absolute scale of temperature. The Kelvin scale is a fundamental quantity in various areas of chemistry, including measurements, the ideal gas law, collision theory, and the study of spontaneity.

5 Must Know Facts For Your Next Test

1. The Kelvin scale is a temperature scale where the lowest possible temperature, absolute zero, is defined as 0 K.
2. One Kelvin is equal to one degree Celsius, but the Kelvin scale starts at absolute zero, while the Celsius scale starts at the freezing point of water.
3. The Kelvin scale is used to measure the absolute temperature of a system, which is the total thermal energy of the particles within that system.
4. The ideal gas law, $PV = nRT$, uses the Kelvin scale to relate the pressure, volume, amount, and temperature of an ideal gas.
5. The Kelvin scale is crucial in understanding the spontaneity of chemical reactions, as the absolute temperature is a key factor in determining the Gibbs free energy change.

Review Questions

• Explain how the Kelvin scale is used to measure temperature and its relationship to the Celsius scale.
  • The Kelvin scale is the base unit of temperature in the International System of Units (SI). It is an absolute temperature scale where the lowest possible temperature, absolute zero, is defined as 0 K. Unlike the Celsius scale, which starts at the freezing point of water (0°C), the Kelvin scale starts at absolute zero. One Kelvin is equal to one degree Celsius, but the Kelvin scale provides a more fundamental measure of the total thermal energy of a system, as it is directly proportional to the average kinetic energy of the particles within that system.
• Describe the role of the Kelvin scale in the ideal gas law and how it relates to the behavior of gases.
  • The ideal gas law, $PV = nRT$, uses the Kelvin scale to relate the pressure (P), volume (V), amount of substance (n), and absolute temperature (T) of an ideal gas. The Kelvin scale is crucial in this equation because it provides a direct measure of the total thermal energy of the gas particles, which is a key factor in determining the behavior of the gas. As the temperature measured in Kelvin increases, the average kinetic energy of the gas particles also increases, leading to changes in the pressure, volume, and other properties of the gas.
• Explain how the Kelvin scale is used to understand the spontaneity of chemical reactions and the concept of Gibbs free energy.
  • The Kelvin scale is essential in understanding the spontaneity of chemical reactions, as it is a key component in the calculation of Gibbs free energy change ($ extbackslashDelta G$). Gibbs free energy is defined as $ extbackslashDelta G = extbackslashDelta H - T extbackslashDelta S$, where $ extbackslashDelta H$ is the change in enthalpy, $ extbackslashDelta S$ is the change in entropy, and T is the absolute temperature measured in Kelvin. The Kelvin scale provides the necessary temperature information to determine whether a reaction will be spontaneous ($ extbackslashDelta G < 0$) or non-spontaneous ($ extbackslashDelta G > 0$), based on the balance between the changes in enthalpy and entropy. This understanding of spontaneity is crucial in predicting the feasibility and direction of chemical processes.

Related terms

Absolute Zero:

The lowest possible temperature, equal to -273.15 degrees Celsius or 0 Kelvin, at which the thermal motion of atoms and molecules reaches its minimum.

Thermodynamic Temperature: The temperature measured on the Kelvin scale, which is the base unit of temperature in the International System of Units (SI).

Thermal Energy:

The total kinetic energy of the random motion of the particles (atoms or molecules) in a substance, which is directly proportional to the temperature measured in Kelvin.