Week 1 Flashcards
What is the first law of Thermodynamics ? Also known as?
When any closed system is taken through a cycle, the net work done on the system by the surroundings is exqual to the net heating done by the system on the surroundings also the net work delivered to surrounding is equal to the net heating done by the surroundings
In an isolated system there will be no work or heating so the total energy of the system will remain constant.
Energy cannot be created or destroyed but only changed from one type to another
Law of conservation of energy
Describe what occurs in an internal combustion engine and how it displays the first law
Energy occurs in the form of chemical bonds in the fuel, when it burns bonds are broken down and released as thermal energy in an exothermic reacj which heats the fluid (air) in the engine which then expand to work on pistons which rotate crank shafts
What are capital sources vs income sources ? What is most available energy in nature vs lowest ? How was this solved
Capital finite I.e fossil fuels, earths energy, chemical direct conversion
Income solar energy
Most energy is thermal energy which is then changed to mechanical energy
Lots of thermal energy stuff to burn but lower sources of mechanical energy
Creation of the heat engine which takes a source of heat and turns some off it into usable mechanical energy.
What is a system? Types and definitions?
A system is a identifiable collection of matter upon which our attention is focused
A composite system is a one broken down into a number of subsystems.
A closed system is a system surrounded by an impermeable barrier meaning matter cannot enter or leave the system
Isolated system means the system cannot interact with its surroundings in anyway. Is a type of closed system
What is a property? Specific property? Extensive intensive?
A measurable characteristic of a system I.e volume pressure, temperature
Specific property? A property divided by mass it gives property of a substance rather than a system
I.e specific volume V/M
Extensive: a property whose value for a composite system ks equal to the sum of values for its subsystems
Intensive: A property whose value for a composite system is not equal to the sum of values for its subsystems
State? Equilibrium? Process? Real process? Quasi-Equilibrium process?
The state of a system at an instance is defined by the values of all its properties at that instance
Equilibrium: a state where all the properties of a system are constant I.e isolated system left for an infinitely long time
Process: Any change from one equilibrium state to another
Real process: A real process will take the system through any number of non-equilibrium states in moving from one Equilibrium to another
Quasi-equilibrium: A process which occurs infinitely slowly and hence the system moves seamlessly through a series of equilibrium states. Can never happen in practice but calculations based on ideal Quasi-Equilibrium processes give useful results by indicating trends and providing performance targets.
What is a cycle?
A system is said to have undergone a cycle of it undergoes a series of processes such that it eventually returns to its original state. I.e all properties return to their original values
The sum of work done on the system throughout the cycle is zero
When is work done positive or negative?
Work done on a system by the surroundings is positive
Work done by the system on its surroundings is negative
Internal energy? E vs Total energy E*
E* include the potential and kinetic energy of the mass
Internal energy related to motion at the atomic and molecular level
W + Q = E2 - E1
E1 state 1 E2 state 2
W & Q Work done and heating
Mass? Volume?
Quantity of matter which the body contains as is measured by its acceleration under a given force exerted on it by a gravitational field?
Amount of space occupied by a substance
Six properties of simple fluids?
Pressure, Temperature, specific volume, specific internal energy, specific enthalpy, specific entropy
Specific enthalpy?
H = e + Pv
Two important corollaries of the entropy postulate other wise known as first law of thermodynamics
- If a system is allowed to interact with its surroundings and is then isolated after a period of settling down (equilibrium) the entropy of the resulting system will have obtained its maximum value
- An ideal process for an isolated system for which entropy remains constant is called a reversible process since it could spontaneously reverse itself without entropy needing to decrease.
What is an important characteristic of a Simple fluid?
Two property rule which states that for equilibrium states of a closed system containing a simple fluid, if two properties,are known and fixed then the others will have unique values and can be evaluated
Ideal gas equation?
P v = R T
Boyles law?
PV = constant
At constant temperature as pressure increases, volume decreases proportionally
Charles?
V/T= constant
At constant pressure as temperature increases. Volume increase by the same,proportion
Gay-Lussac’s Law
P/T = constant
At constant volume, as temperature increases, pressure increases by the same proportion
What is the specific ideal gas constant?
Ris a constant particular to the fluid under consideration and can be calculated using
R = Ru/M = approx R/M where Ru = 8.314 and M molar mass
What is the kinetic theory of gases? What does it assume?
Model behaviour of gases from a fundamental point assuming
Average distance separating molecules is large compared to size
Particles have same mas
Number of particles is so large that statistical treatment can be applied
Interactions among particles are negligible
Average kinetic energy of the particles depend on,y on absolute temperature of the system
When do the ideal gas laws break down?
Temperature is too low molecules are moving slowly and near each other for a long time meaning they can interact so assumptions will be violated
Pressure is too high because particles will be squashed and break theory
What is compressibility factor?
Z = PV/RT = v actual/v ideal
What is the principle of corresponding states
If the value of Z were know we have a. Corrected ideal gas equation for all temperatures and pressure
Pseudo-reduced volume/
Vr = v actual/(RTcrit/Pcrit)
