Thermodynamics: Introduction, Dimensions, and Units

Chapter 1. Introduction

• Thermodynamics studies energy and its transformations.
• Determines the energy needed for chemical reactions.
• Determines equilibrium conditions for chemical reactions and phase transitions.

Dimensions and Units

• Dimensions describe physical quantities, like length, time, and mass.
• Units express the magnitude of dimensions, such as meters, seconds, and kilograms.

SI System

• The International System of Units (SI) is the standard unit system.
• Base SI units include meter (m) for length, kilogram (kg) for mass, second (s) for time, Kelvin (K) for temperature, and mole (mol) for amount of substance.
• Other base SI units are ampere (A) for electric current and candela (cd) for luminous intensity.

English System

• The English System is also known as the US Customary System.
• Base units include foot (ft), pound (lb), second (s), and Rankine (°R).

Conversion of Units

• Units can be changed using conversion factors.
• For example: 20 ft is equal to 6.096 m ($20 \ ft \times \frac{0.3048 \ m}{1 \ ft} = 6.096 \ m$).

Measures of Amount or Size

• Mass (m) is the amount of matter in an object, measured in kg or lb.
• Volume (V) is the space occupied by an object, measured in $m^3$ or $ft^3$.
• Density ($\rho$) is mass per unit volume ($\rho = \frac{m}{V}$).
• Specific Volume ($\hat{V}$) is volume per unit mass ($\hat{V} = \frac{V}{m} = \frac{1}{\rho}$).
• Mole (n) is the amount of substance containing Avogadro's number of entities ($6.022 \times 10^{23}$).
• Molar Volume ($\bar{V}$) is volume per mole ($\bar{V} = \frac{V}{n}$).

Force

• Force (F) is mass times acceleration ($F = ma$).
• The SI unit for force is Newton (N), where $1 \ N = 1 \ kg \cdot m/s^2$.
• The English unit for force is pound-force (lbf).

Weight

• Weight (W) is the force exerted on an object due to gravity.
• Calculated by $W = mg$, where g is the acceleration due to gravity ($g \approx 9.81 \ m/s^2$ or $32.2 \ ft/s^2$).

Temperature

• Temperature is a measure of the average kinetic energy of molecules in a system.
• Celsius (°C) is related to Kelvin (K) by $T(^{\circ}C) = T(K) - 273.15$.
• Fahrenheit (°F) is related to Celsius (°C) by $T(^{\circ}F) = 1.8 \times T(^{\circ}C) + 32$.
• Kelvin (K) is an absolute temperature scale.
• Rankine (°R) is an absolute Fahrenheit scale, $T(^{\circ}R) = T(^{\circ}F) + 459.67$.

Pressure

• Pressure (P) is force per unit area ($P = \frac{F}{A}$).
• The SI unit for pressure is Pascal (Pa), $1 \ Pa = 1 \ N/m^2$.
• Other units for pressure include bar, atm, and psi.

Pressure Measurement

• Absolute Pressure is pressure relative to a perfect vacuum.
• Gauge Pressure is pressure relative to atmospheric pressure ($P_{gauge} = P_{absolute} - P_{atmospheric}$).
• Vacuum Pressure is pressure below atmospheric pressure.

Work

• Work (W) is energy transferred when a force acts over a distance ($W = \int F \cdot dx$).
• The SI unit for work is Joule (J).
• The English unit for work is ft·lbf.

PV Work

• PV Work is work done by expansion or compression of a gas.
• The formula for PV Work is $W = \int P \ dV$.

Energy

• Energy (E) is the capacity to do work.
• Kinetic Energy (KE) is energy due to motion ($KE = \frac{1}{2}mv^2$).
• Potential Energy (PE) is energy due to position ($PE = mgh$).
• Internal Energy (U) is energy due to molecular structure and activity.
• SI unit for energy is Joule (J).

Heat

• Heat (Q) is energy transferred due to temperature difference.
• The SI unit for heat is Joule (J).

Heat Capacity

• Heat Capacity (C) is energy required to raise the temperature of a substance by one degree ($C = \frac{Q}{\Delta T}$).
• Specific Heat Capacity (c) is heat capacity per unit mass ($c = \frac{C}{m}$).
• Molar Heat Capacity ($\bar{C}$) is heat capacity per mole ($\bar{C} = \frac{C}{n}$).

Equilibrium

• Equilibrium is a state where there are no macroscopic changes with time.
• Thermal Equilibrium means uniform temperature.
• Mechanical Equilibrium means uniform pressure.
• Chemical Equilibrium means no net chemical reactions.