Thermodynamics Test. 5

This fixed point is used to define the Kelvin scale. It is also equivalent to 0.01 °C.

This is the Stefan-Boltzmann law, expressed as P = σAT⁴, which describes the power radiated from a black body.

Thermal conductivity quantifies how effectively a material transfers heat through conduction.

Efficiency measures how effectively a device converts the heat it receives into useful work.

The van der Waals equation provides a more realistic model for the behavior of real gases by correcting for molecular size and attraction.

This law is an approximation that applies when the temperature difference between the object and its surroundings is small.

The unit for thermal conductivity is watts per meter-Kelvin.

According to the second law of thermodynamics, the entropy of the universe (an isolated system) always increases in any spontaneous process.

This is a key property of enthalpy, making it very useful for analyzing processes that occur at constant pressure, such as many chemical reactions.

Helmholtz free energy (A) is defined as internal energy (U) minus the product of temperature (T) and entropy (S). It represents the 'useful' work obtainable from a closed system at constant temperature and volume.

A reversible process is defined as one that can be reversed by an infinitesimal change in conditions, ensuring the system remains in equilibrium throughout.

This is described by Fourier's law of heat conduction, which states that the rate of heat flow is proportional to the area and the temperature gradient.

Emissivity is a measure of how well a surface radiates energy. A perfect black body is a perfect emitter, so its emissivity is 1.

A negative change in Gibbs free energy (ΔG < 0) indicates that a process is spontaneous under these conditions.

All real-world processes are irreversible due to factors like friction, heat loss, and other dissipative effects that increase the total entropy.

The Kelvin scale is the standard thermodynamic temperature scale, as it is based on an absolute zero point.

This law (λ_max = b/T) explains why hotter objects glow with shorter wavelengths (e.g., from red hot to white hot).

For an isobaric (constant pressure) process, work done is W = PΔV. First, convert pressure: 150 kPa = 150,000 Pa. The change in volume is ΔV = 0.5 m³ - 0.2 m³ = 0.3 m³. So, W = 150,000 Pa * 0.3 m³ = 45,000 J, which is equal to 45 kJ.

Enthalpy (H) is a thermodynamic property defined as the sum of the internal energy (U) and the product of pressure (P) and volume (V).

A black body is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence.

According to the First Law of Thermodynamics, ΔU = Q - W. Here, Q is positive (+2000 J) because heat is absorbed, and W is positive (+500 J) because work is done by the system. Therefore, ΔU = 2000 J - 500 J = 1500 J.

Gibbs free energy (G) is defined as enthalpy (H) minus the product of temperature (T) and entropy (S).