Temperature, Heat, and the First Law of Thermodynamics Chapter 18 Temperature, Heat, and the First Law of Thermodynamics

Temperature Thermodynamics – branch of physics studying thermal energy of systems Temperature (T), a scalar – measure of the thermal (internal) energy of a system SI unit: K (Kelvin) Kelvin scale has a lower limit (absolute zero) and has no upper limit William Thomson (Lord Kelvin) (1824 - 1907)

Kelvin scale Kelvin scale is defined by the temperature of the triple point of pure water Triple point – set of pressure and temperature values at which solid, liquid, and gas phases can coexist International convention: T of the triple point of water is

The zeroth law of thermodynamics If two (or more) bodies in contact don’t change their internal energy with time, they are in thermal equilibrium 0th law of thermodynamics: if bodies are in thermal equilibrium, their temperatures are equal

Measuring temperature Temperature measurement principle: if bodies A and B are each in thermal equilibrium with a third body T, then A and B are in thermal equilibrium with each other (and their temperatures are equal) The standard temperature for the Kelvin scale is measured by the constant-volume gas thermometer

Constant-volume gas thermometer

Celsius and Fahrenheit scales Celsius scale: Fahrenheit scale: Anders Cornelius Celsius (1701 - 1744) Gabriel Daniel Fahrenheit (1686 - 1736)

Thermal expansion Thermal expansion: increase in size with an increase of a temperature Linear expansion: Volume expansion:

Chapter 18 Problem 19

Temperature and heat Heat (Q): energy transferred between a system and its environment because of a temperature difference that exists between them SI Unit: Joule Alternative unit: calorie (cal):

Q Q Absorption of heat Specific heat (c): heat capacity per unit mass Common states (phases) of matter: solid, liquid, gas Heat of transformation (L): the amount of energy per unit mass transferred during a phase change (boiling, condensation, melting, freezing, etc.) Q Q

Chapter 18 Problem 37

Heat and work Thermodynamic cycle

The first law of thermodynamics Work and heat are path-dependent quantities Quantity Q – W = Eint (internal energy) is path-independent 1st law of thermodynamics: the internal energy of a system increases if heat is added to the system and decreases if work is done by the system

The first law of thermodynamics Adiabatic process: no heat transfer between the system and the environment Isochoric (constant volume) process Free expansion: Cyclical process:

Chapter 18 Problem 48

Heat transfer mechanisms Thermal conduction Conduction rate: Thermal resistance: Conduction through a composite slab: Thermal conductivity

Heat transfer mechanisms Thermal radiation Radiation rate: Stefan-Boltzmann constant: Absorption rate: Emissivity Josef Stefan (1835-1893) Ludwig Eduard Boltzmann (1844-1906)

Chapter 18 Problem 52

Heat transfer mechanisms Convection

Heat transfer mechanisms

Answers to the even-numbered problems Chapter 18: Problem 4 320º F; (b) -12.3º F

Answers to the even-numbered problems Chapter 18: Problem 10 1.1 cm

Answers to the even-numbered problems Chapter 18: Problem 22 109 g

Answers to the even-numbered problems Chapter 18: Problem 44 − 200 J; (b) − 293 J; (c) − 93 J

Answers to the even-numbered problems Chapter 18: Problem 50 0.42 m; (b) 7.4 km