Thermodynamics lecture 2 Flashcards
What are the critical constants? (the answer explains the whole concept so waffle)
there is a critical temperature that separates two regions of the compound’s behavior.
Below this critical temperature the fluid as we know it is normal. When a certain pressure is applied to compress a liquid it condenses and forms a gas at which the horizontal barrier between the two phases is very clear, but when this compression is applied at a critical temperature or above the two phases merge into one single point known as the critical point of the gas, the molar volume and pressure at that critical point are known as the critical molar volume and the critical pressure.
The sample at Tc and past it is considered to be the same phase which is a gas, but the gas formed is much denser than what gases usually are so this substance is rather called a supercritical liquid.
what are the van der waals loops
for temperature below the critical temperature, the isotherm for a gas oscillates forming a minima followed by a maximum in a pressure against volume graph. This is not possible as the increase in pressure doesn’t lead to an increase in volume therefore a horizontal line is drawn in the midpoint of osocialation instead of the maxima and the minina where the line splits the two curves into equal areas, such technique is known as the maxwell construction.
What are the 3 principal features of the van der waals equation of state?
- perfect gas isotherms are obtained at very high temperatures and large molar volumes - With large temperatures, the first term becomes much more significant than the second term, and the molar volume because much larger than the repulsive constant so the equation becomes a perfect gas equation
- liquid and gases coexist when the repulsive and attractive forces are in balance - the first term and second term of the equation become similar and this causes the van der Waal’s loops
- The critical constants are related to the van der waals equation - at temperatures below the critical temperatures the graph oscillates with minima and maxima which will get smaller as the temperature approaches the critical temperature, Once the temperature reaches the critical temperature the maxima and minima converge causing a point of inflection. A point of inflection of that type has its first and second derivatives equal to zero so the critical constants can be found by setting the first and second derivatives to zero
what are the 3 equations that relate the critical values to van der Waal’s equation? How can we test that?
- Tc = 8a/27bR
- Pc = a / 27b^2
-Vc = 3b
It can be tested by noting the compression critical value Zc = PcVc/RTC = 3/8
What are the reduced variables of critical values?
- Tr = T/Tc
- Pr = P/Pc
- Vr = V/Vc
What is the principle of corresponding states?
it is the observation that real gases at the same reduced volume and reduced temperature exert the same reduced pressure.
note: this works best for gases composed of spherical molecules and works horribly with polar molecules.
What is van der waals reduced equation of state
Pr = [8RTr/(Vr -1)] - [3/Vr^2]
what are the different types of systems in physical chemistry?
- open system - allows transfer of both matter and heat between the system and the surroundings
- closed system - allows only transfer of heat between the system and the surrounding
- isolated system - allows no transfer of heat or matter between the system and the surrounding
what is work, energy, and heat? What relation do they have with each other?
work is done to achieve motion against an opposing force.
Energy is the ability to do work.
Heat is thermal energy transferred between the system and the sounding due to a temperature difference.
When work of done on a system the energy increases when work is done by the system the energy of the system decreases, when heat is applied to the system work done by the system increases therefore the energy of the system decreases
what are diathermic and adiabatic boundaries?
diathermic allows for the transfer of heat
adiabatic doesn’t allow the transfer of heat
What happens to exothermic and endothermic processes in adiabatic and diathermic boundaries
Adiabatic - since the reaction occurs in an isolated system the endothermic or exothermic process would then have a permanent change in temperature. (with endothermic decreasing temp and exothermic increasing temp)
Diathermic - since the reaction doesn’t occur in an isolated system there will be no permanent temperature change in the system when endothermic or exothermic reactions take place, that is because heat is transferred between teh system and teh boundaries, so the temp might increase or decrease initially but eventually it will return to the room temp
what is the difference between heat and work applied to a system?
work is the transfer of energy that makes use of the organized motion of the surroundings, on the other hand, heating is the transfer of energy that makes use of disorderly motion known as thermal motion.
This means when work is done on or by a system, the molecules are moving in an organized way, but when heat is transferred to or from the system the motion of particles is random
what is the internal energy, change internal energy, and molar internal energy?
internal energy is the total energy of a system and it is composed of kinetic and potential energy, it is a state function meaning that it is dependent on the current state of a system and not how it was prepared.
Change in internal energy is equal to Uf -Ui
molar Internal energy is the internal energy divided by the amount of substance.
what is special about the internal energy in a perfect gas
the internal energy of a perfect gas is independent of the volume occupied as we assume in a perfect gas that the molecules don’t interact therefore the distance between the molecules is irrelevant and the internal energy is only dependent on the kinetic energy of the molecules.
what is the first law of thermodynamics?
the first law of thermodynamics states that in an isolated system, the amount of internal energy is constant. The first law is further defined by U = q + w where this indicates that heat and work are equivalent ways of changing the internal energy of a system.
