Thermodynamics Flashcards
What is the theory of mechanical equivalent of heat?
It is the theory that the mechanical work can be transferred to heat energy, and the converse that heat energy can be transferred to mechanical work.
It also important that the magnitude of one is proportional to the other.
What is the zeroth law of thermodynamics?
If two thermodynamic systems are separately in equilibrium with a third system, then they must also be in equilibrium with each other.
The implication of this law is that if two systems or objects at the same temperature are placed in thermal contact with one another, they will be in thermal equilibrium, and heat energy will not flow from one system to the other.
Explain how a thermometer works by using the laws of thermodynamics.
A column of mercury in a thermometer is put into contact with a second thermodynamic system until a reference point is reached (e.g freezing/boiling point of water) using this reference points can be made on the thermometer.
If you now take the thermometer and put in contact with a third thermodynamic system (say a human armpit) the temperature can be determined by the observation of the change in the thermal property of the thermometer.
This can be achieved as a result of the zeroth law.
What is the first law of thermodynamics?
Energy can neither be created nor destroyed. Energy can only be transferred from one form to another. Therefore the total energy in a system will remain constant.
Explain the venturi principle?
As a fluid passes through a narrowing in a tube the kinetic energy will increase* but at the expense of potential energy e.g pressure. As the pressure drops past the narrowing in the tube this can be used to entrail a second fluid/gas.
*think about putting your thumb over the end of part a hose
Give examples of the venturi principle being used in medicine?
Nebulisers utilise the venturi principle, there is a narrowing in a nebulisation device which increases kinetic energy and therefore drops the pressure. This entrains air which bubbles through the liquid which needs to be nebulised.
Venturi masks as expected use the venturi principle, the amount of air that gets entrailed depends on the size of the holes in the venturi attachments. The larger the holes the more air that can get entrailed and therefore the lower the FiO2 delivered.
What is an adiabiatic process?
It is a process in which a change in the system occurs without any exchange of heat energy from the surroundings.
An example of this is if a gas expand rapidly, energy is required to overcome the van der vaal forces of attraction which comes in the form of kinetic energy. As the kinetic energy to overcome these forces increases there is a corresponding drop in heat energy.
Conversely as you rapidly compress a gas the gas will increase in temperature.
What is the Second law of thermodynamics?
Known as the law of increased entropy. Entropy tends to increase over time and is a measure of chaos or disorganisation – may be thought of as a measure of unavailable energy.
Consider dropping a glass breaking as it smashes some of the energy in the system will have be transferred to sound and heat energy, although the energy has not been lost it is now unavailable.
What is the third law of thermodynamics?
As a system approaches the absolute zero all processes cease and the entropy of the system approaches a minimum value.
Can absolute zero ever be achieved?
No by nature of the 2nd law of thermodynamics of entropy increasing over time. If absolute zero is achieved entropy will be 0.
As a system approaches absolute zero heat energy will be drawn from surrounding systems.
What is the combined law of thermodynamics?
The Combined Law
Is simply a mathematically derived summation of the first and second laws subsumed into a single concise mathematical statement that relates distribution of kinetic or thermal energy and entropy, showing how little this will change overall energy in the system:
ΔU = TΔS + pΔV ≤ 0
Where…
U = Internal Energy of the system
T = temperature
S = Entropy
P = pressure
V = Volume
