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
- 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 ∝)
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
- 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
- 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 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.
- 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.