Thermodynamics and Heat Transfer Vocabulary (Lecture Notes)

Vocabulary flashcards covering temperature scales, heat, density, buoyancy, gas laws, thermodynamics, and related concepts from the lecture notes.

Celsius scale (centigrade)

A temperature scale defined by 0°C as the freezing point and 100°C as the boiling point of water; centigrade means 100 degrees.

Absolute zero

The lowest possible temperature (0 K) at which molecular motion would stop; unattainable in practice.

Kelvin

The absolute temperature scale; relation to Celsius is T(K) = T(°C) + 273.15.

Specific heat capacity

The amount of heat required to raise the temperature of 1 kg of a substance by 1°C; units are kJ/(kg·°C).

Latent heat of fusion

The heat required to melt 1 kg of a solid at its melting point without changing its temperature (ice ≈ 335 kJ/kg).

Density

Mass per unit volume; varies with temperature due to thermal expansion; most substances expand and become less dense as temperature rises.

Ice vs water density (floating ice)

Ice is less dense than liquid water, so it floats; when floating ice melts, the water level in a closed container remains unchanged.

Buoyancy

Upward force on an object immersed in a fluid due to pressure differences; equals the weight of the displaced fluid.

Archimedes’ principle

The buoyant force on a submerged object equals the weight of the fluid it displaces.

Pressure

Force per unit area; in fluids, increases with depth; measured in pascals (Pa).

Boyle’s law

For a fixed amount of gas at constant temperature, pressure and volume are inversely related: P1V1 = P2V2.

Charles’s law

For a gas at constant pressure, volume is proportional to absolute temperature: V1/T1 = V2/T2 (temperatures in Kelvin).

Ideal gas law

PV = nRT; relation among pressure, volume, temperature, and amount of gas.

Temperature conversions

Converting between Celsius, Fahrenheit, and Kelvin; examples: 0°C = 32°F = 273.15 K; −40°C = −40°F; 0 K = −273.15°C.

Kinetic theory

At a given temperature, gas molecules have the same average energy; individual speeds vary with molecular mass; lighter molecules move faster.

Evaporation

Phase change from liquid to gas at the surface; absorbs latent heat and cools the liquid; rate depends on surface area, temperature, and vapor pressure.

Melting

Phase change from solid to liquid at the melting point; involves latent heat of fusion.

Heat transfer

Mechanisms by which heat moves: conduction (through solids), convection (in fluids), and radiation (electromagnetic waves).

Q = mcΔT

Heat energy formula: Q is heat, m is mass, c is specific heat, ΔT is change in temperature.

First law of thermodynamics

Energy is conserved; heat added to a system equals work done plus change in internal energy.

Second law of thermodynamics

Entropy tends to increase; no real engine can be 100% efficient between two reservoirs; need a hot and a cold reservoir to do work.

Entropy

A measure of the disorder of a system; increases in natural processes; local decreases (e.g., in organisms) are offset by larger increases elsewhere.

Carnot (maximum) efficiency

ηmax = 1 − Tcold/Thot for an ideal engine operating between Thot and Tcold; serves as an upper bound on real efficiencies.