# Thermodynamics

#### Zeroth Law of Thermodynamics

• If temp of A=temp of B & Temp of B= Temp of C then temp of A=temp of C
• Temperature is proportional to average kinetic energy.
• Heat refers to the transfer of thermal energy from something hot to something cold
• Kelvin Scales: absolute zero is the theoretical temperature where there is no thermal energy.
• Third Law states that the entropy of a perfectly-organized crystal at absolute zero is zero.
• F = 9/5 C + 32
• K = C + 273

##### Thermal Expansion
• This equation is used for solids: ΔL = ∝ LΔT
• For liquids only meaningful parameter is the volume expansion: ΔV = βVΔT
• The value of b is three times the coefficient of linear expansion (b = 3 ∝)

#### Systems

A system is the portion of the universe that we are interested in observing or manipulating. The rest is called surroundings.

• Isolated Systems: Not capable of exchanging energy or matter with their surroundings. Total change in internal energy must be zero.
• Closed Systems: Capable of exchanging energy, but not matter with the surroundings.
• E.g – gas in vessels with moveable pistons
• Open Systems: Can exchange both matter and energy with the environment.
• State Functions: thermodynamic properties are a function of only the current equilibrium state. These are defined by the fact that they are path independent.
• E.g – Pressure, density, temperature, volume, enthalpy, internal energy, Gibbs free energy, and entropy
• Process Function: describe the path taken to get from one state to another
• E.g. – Work and Heat

#### First law of Thermodynamics

Just another iteration of the energy conservation law (energy cannot be created or destroyed).

• ΔU = Q-W

##### Heat
• Second Law of Thermodynamics: objects in thermal contact and not in thermal equilibrium will exchange heat energy.
• Heat: defined as the process by which a quantity of energy is transferred between two objects as a result of difference in temperature.
• Unit is Joule, but can also be in calories (c), nutritional calories (C), and British thermal unit (BTU).
• One calorie is the amount og heat required to raise 1g of water by 1 degrees
• 1 Cal = 10^3 cal = 4184 J = 3.97 BTU

##### Heat Transfer
• Conduction: direct transfer of energy from molecule to molecule through molecular collisions.
• Metals are the best conductors while gases are the worst
• Convection: transfer of heat by the physical motion of a fluid over a material. Only for liquids and gases since it needs the movement of a fluid.
• Radiation: transfer of energy by electromagnetic waves. Can transfer energy through a vacuum.

##### Specific Heat
• Specific heat of a substance is defined as the amount of heat energy required to raise one gram of a substance by one degree Celsius or one-unit kelvin.
• Specific heat of water is 1 cal/(g*K)  or 4.184 J/(g*K)
• q = mcΔT

##### Heat of Transformation
• Phase change occurs at a constant temperature since these changes are related to changes in potential energy and not kinetic energy.
• Increasing the temperature of a substance undergoing a phase change will increase the potential energy which permits a greater number of microstates (ability to move).
• q = mL where L is the heat of transformation or latent heat
• Liquid to solid is freezing/solidification; solid to liquid is melting/fusion and it occurs at the melting point and heat of transformation is called the heat of fusion.
• Liquid to gas is boiling/evaporation/vaporization; gas to liquid is condensation and this occurs at the boiling point and heat of transformation is called the heat of vaporization.

##### Thermodynamic Processes
• Have three particular processes that are focused on isothermal, adiabatic and isovolumetric.
• Thermodynamic processes can be showed on a P-v or T-V diagram.

#### Second Law of Thermodynamics and Entropy

• Energy Dispersion: Energy goes from being concentrated to being spread out.
• Entropy is a measure of how spontaneous a reaction will be.
• ΔS = Qrev/T
• ΔSuniverse = ΔSsystem + ΔSsurroundings > 0
• Naturally Process: Something that intuitively occurs
• Reversible Reaction: processes that can spontaneously reverse course. This only occurs when the system is always in equilibrium, as such an infinite time period would be needed.

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