Internal Energy, Temperature, and Thermodynamics Lecture Notes

Vocabulary-style flashcards covering internal energy, temperature scales, laws of thermodynamics, and thermal expansion based on the lecture notes.

Internal Energy

The energy associated with the random, disordered motion of molecules within a substance.

Absolute Zero

The condition under which molecular motion ceases, occurring at $-273.15^{\circ}C$ or $0\,K$.

Ordered Motion

Molecular motion where all molecules move in the same direction, such as a speeding bullet; this is not classified as internal energy.

Temperature

A measure of the average kinetic energy of disordered molecular motion, though not directly proportional to the entire internal energy.

Thermal Equilibrium

A state where two objects are at the same temperature, resulting in no net transfer of internal energy between them.

Heating

The transfer of internal energy from a high-temperature object to a lower-temperature object, often via collisions of energetic molecules at the boundary.

Standard Atmospheric Pressure

The universal standard for temperature scales, defined as $760\,mm\,Hg$, used specifically to calibrate the boiling point of water.

Celsius (Centigrade) Scale

A temperature scale where the freezing point of water is $0^{\circ}C$ and the boiling point is $100^{\circ}C$ at standard pressure.

Kelvin (Absolute) Scale

An SI base unit scale where the zero point is absolute zero, sharing the same degree size as the Celsius scale ($T_K = T_C + 273.15$).

Fahrenheit Conversion Formula

The mathematical relationship used to convert Celsius to Fahrenheit: $T_F = \frac{9}{5}T_C + 32$.

First Law of Thermodynamics

The application of the conservation of energy principle to heat and internal energy, represented by the equation $\Delta U = Q + W$.

Heat ($Q$)

Often described as "internal energy in transit," it is the energy transferred between systems due to a temperature difference via microscopic processes.

Work ($W$)

The macroscopic process of changing internal energy, such as the compression of a gas.

Isothermal Expansion

A process where a gas expands and performs work ($W < 0$) equal to the heat added ($Q$), resulting in $\Delta U = 0$ and a constant temperature.

Thermal Expansion

The increase in the dimensions of a body caused by atoms vibrating over greater distances as temperature increases.

Linear Expansion Equation

The formula describing expansion in one dimension: $\Delta l = \alpha l \Delta T$, where $\alpha$ is the coefficient of linear expansion.

Pyrex

A type of glass with a coefficient of linear expansion ($\alpha$) less than half that of ordinary glass, making it less likely to crack when heated.

Bimetallic Strip

A temperature-measuring device made of two bonded metals with different coefficients of expansion ($\alpha$) that bends proportionally to temperature changes.

Constant Volume Gas Thermometer

A thermometer based on the ideal gas law, where the pressure of an enclosed gas is directly proportional to the Kelvin temperature ($P = BT$).

Specific Heat ($c$)

The amount of heat in calories required to raise the temperature of $1\,g$ of a substance by $1^{\circ}C$.

Calorie (cal)

The unit of heat or internal energy required to raise the temperature of $1\,g$ of water by $1^{\circ}C$.

Dietary Calorie (Cal)

A unit equal to $1000\,cal$ or $1\,kcal$, used to express the energy value of foods.

Heat of Combustion

The energy released from food during oxidation, typically measured by burning the substance in a pure oxygen atmosphere inside a calorimeter.

Mechanical Equivalent of Heat

The principle demonstrated by James Joule that mechanical work can be converted to heat, established as $1\,cal = 4.186\,J$.