Thermodynamics Flashcards
What are the laws of thermodynamics?
0th Law: If two
systems are each in thermal equilibrium with a third system, then they are in thermal equilibrium
with each other.
1st Law: Conservation of energy - ΔU=q+w
2nd Law: Entropy never decreases - ΔS(universe)=ΔS(system)+ΔS(surroundings)>0
3rd Law: There exists a temperature minimum of absolute zero - S(T=0)=0 for a pure crystal with no defects
What are the three broad types of energy?
Kinetic Energy: energy of motion, translation, and rotation
Potential Energy: energy related to position within a potential field
Internal Energy: energy related to the internal properties of an object or particle, like temperature
What are state versus path dependent variables, and what are the path dependent variables?
State variables are defined only by the current state of the system, like temperature, volume, and pressure
Path dependent variables define a process and can be different even if the start and end points are the same: the two path dependent variables are heat and work
Define extensive versus intensive properties with examples
Extensive: property of the system as a whole like volume, number of moles, or entropy
Intensive: property that is independent of the size of the system, like temperature and pressure
What are the steps of the Carnot cycle and what are it’s properties?
Steps: isothermal expansion, adiabatic expansion. isothermal compression, adiabatic compression
Most efficient cycle, reversible cycle, efficiency is difference between high and low temperature divide by high temperature, or 1-Qc/Qh
Makes a rectangle on a TS diagram, going clockwise, step one is top left
In the PV diagram the right side is stretched down, P1>P2>P4>P3; V3>V2>V4>V1
What are Raoult’s and Henry’s Laws?
Describes the partial pressure of solutions
Raoult’s Law for an ideal solution: Pi=XiP*I
(partial pressure, mole fraction in liquid, equilibrium vapor pressure of pure component)
Henry’s Law for a real solution at low concetration: C=kP (concentration, Henry’s constant, partial pressure)
What is spinodal decomposition?
Spinodal decomposition is a special case of phase transformation when a single phase separates into two without nucleation (spontaneously), and happens upon cooling
Characterized by nested curves (binodal) on a phase diagram and a sin-esque Gibb’s free energy curve, the part of the curve which is concave downwards is the spinodal region
What is the miscibility gap?
Part of the phase diagram consisting of two phases, meaning that they are not soluble, or miscible
This happens when the enthalpy of mixing is positive
How does the weather affect the efficiency of a thermodynamic cycle?
It will be less efficient on hot days, the efficiency of a thermodynamic cycle is best when Tc and Th have a large difference
Explain how adding more reactants or products to a system already in equilibrium will affect it.
Adding more reactants will make the reaction proceed more, adding products can make it reverse; if you add heat to an exothermic reaction it can slow it down or reverse it
What are the two kinds of free energy?
Gibbs free energy: related to temperature and pressure; maximum amount of non-volume expansion work that can be performed by a closed system
Helmholtz free energy: related to temperature and volume
What is the importance of Maxwell Relations?
Maxwell relations show that a thermodynamic second derivative is not changed by the order, allowing different equivalents to be created depending on the need of the problem
How can you create Gibb’s free energy curves from a phase diagram?
Take a single temperature (though can also be used for pressure) and each phase has an upwards facing curve, tie lines from two curves represent miscibility gaps where two phases are present
What does the GT curve for water look like?
Three straight lines, from left to right representing solid, liquid, and gas, with increasingly negative slopes
What is the formula that represents deviations from ideal gas behavior?
PV=ZRT
Z is the compressibility factor and represents how different a real gas behaves compared to an ideal gas
