Thermodynamics terminology Flashcards
Making sense of all the terms, formulas, and relationships
What is an equation of state?
An equation of state is an equation relating temperature, pressure, and volume of any material
How is the ideal gas equation defined? What do each of the variables mean?
1) pV = mRT
2) pV = (rho)RT
3) p(alpha) = RT
p = pressure (Pa) V = volume (m^3) m = mass (kg) T = absolute temp (K) R = gas constant (depends on gas being studied bu normally universal gas constant) R* = universal gas constant (8.3145 J*K^-1 mol^-1) rho = density (kg / m^3) alpha = specific volume (i.e. volume occupied by 1 kg of the gas @ pressure p and temp T)
What is Boyle’s Law, and what is its connection to the ideal gas law?
Volume of a gas is inversely proportional to its pressure, given fixed mass and temperature.
pV = mRT: If m and T are fixed, V = R/p, which shows inverse proportionality.
What makes a change “isothermal”?
A change is defined as isothermal if a change in state of a substance occurs without a change in temperature, i.e. changes in state occur at constant temperature.
What are Charles’ Two Laws?
1) Given fixed mass and pressure, volume is directly proportional to absolute temperature.
2) Given fixed mass and volume, pressure proportional to absolute temperature.
What is Avogadro’s number, and what does it mean?
6.022 x 10^23. It represents the # of molecules in a mole.
What is Avogadro’s hypothesis?
Gases containing same # of molecules occupy the same volume @ same temperature and pressure.
What’s the IGL? for 1 mol? For any # of moles? Why is this different from the standard IGL??
pV = R*T, where R* is universal gas constant for 1 mol pV = nR*T, where n is # of moles.
These two formulas differ from the other forms of IGL because these have different units (mols) vs the others (g). If pV = mRT was used, mass of the substance will be factored in. However, using R* (which is per mol) automatically factors in the mass per mol of the substance. Therefore, m can be canceled out, yielding these two equations.
What is Boltzmann’s constant, and what does it represent?
Gas constant for one molecule of any gas (symbol: k)
k = R* / N_A, where N_A = Avogadro’s number
Why is virtual temperature important?
Virtual temperature is used in the IGL equation when calculating pressure associated with moist air or vapor. In this case, virtual temperature replaces actual temperature in the equation, and when solving for moist air state variables, the dry air gas constant is still used alongside the virtual temperature.
What is latent heat of vaporization, and how does it relate with temperature?
Latent heat of vaporization is the amount of heat required to change all molecules of a mass of substance into vapor. It decreases with increasing temperature, reaching zero at the critical point of temperature.
What makes a process “adiabatic”?
An adiabatic process occurs when a parcel undergoes a change in state without exchanging heat, i.e. only through expansion and compression of the gas can the gas change temperature.
What is the equation of internal energy of an ideal gas? Describe it in words.
E(T) = (3/2)(N * K_b * T)
Internal energy is directly proportional to the number of particles and the temperature of the substance.
Define the first law of thermodynamics. What is its equation?
The amount of work required to change an isolated system from state 1 to state 2 is independent of how the work is performed.
(delta)E = work = heat in (Q) + W (work in)
and
(delta)E = T(delta)S - p(delta)V, where (delta)S = change in entropy of the system, p(delta)V = work done by a system
No matter how we do work on a system, change of energy is always (delta)E = work in an isolated system.
As shown by the equation, work done by a system decreases the internal energy of the system.
Define Gibbs and Helmholtz energies, and explain what makes them different.
Gibbs energy (G) is a thermodynamic potential and indicates the net energy contribution of a system's internal energy and spontaneous heat transfer from the environment upon the system's creation. Additional work is required to "make room" for the system at final volume V and constant pressure p. Gibbs energy is found from a system at constant pressure and temperature, and it also represents chemical potential times the number of particles in the system. G = internal energy (E) - (T * entropy (S)) + pV, where pV is the work done by the gas on a system at constant pressure p
Helmholtz energy (H) is a thermodynamic potential and indicates the net energy contribution of a system's internal energy and spontaneous heat transfer from the environment upon the system's creation. Helmholtz energy is found from a system at constant temperature and volume; therefore, it does not take into account the work required to "make room" for the system. H = internal energy (E) - (T * entropy (S))
