Thermodynamics- Intro and basic concepts Flashcards
What is thermodynamics?
Heat in motion. The science of energy.
What is classical thermodynamics?
Macroscopic approach to thermodynamics that doesn’t require knowledge of the behaviour of individual particles.
What is a system?
A quantity of matter or a region in space chosen for study
What is a system’s surroundings and boundary?
Surroundings: the mass or region outside the system
Boundary: the real or imaginary surface that separates the system from its surroundings.
What are the similarities and differences between a closed and open system?
No mass can cross the boundary of a closed system (although it can have a moving boundary). Energy can cross the boundary in both.
What is a control surface?
The boundaries of a control volume (real or imaginary)
Define specific gravity
The ratio of the density of a substance to the density of some standard substance at a specified temperature (usually water at 4°C)
What is a property of a system?
Any characteristic of a system used to describe the state. Have numerical value and unit.
Extensive, intensive, specific and molar properties.
Extensive: those whose values depend on the size (or extent) of the system.
Intensive: those whose values are independent of the mass of a system.
Specific: intensive properties per unit mass
Molar: per unit mole
On the molecular level, what is temperature proportional to?
The average kinetic energy of the individual atoms (or molecules) in the system. This is related to the mean square velocity.
What is the Ice point?
A mixture of ice and water that is in equilibrium with air saturated with vapour at 1atm pressure and 0°C temperature.
What is the steam point?
A mixture of liquid water and water vapour (no air) in equilibrium at 1atm pressure and 100°C temperature.
What is a thermodynamic temperature scale?
Independent of the properties of any substance and start at absolute 0. Kelvin and Rankine.
What is the 0th law of thermodynamics?
If two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other.
Define pressure and it’s different types
Pressure: a normal force exerted by a fluid per unit area.
Absolute (P): the actual pressure at a given position measured relative to absolute vacuum.
Gauge: the difference between absolute pressure and local atmospheric pressure.
Vacuum pressures: pressures below atmospheric pressure.
How to calculate pressure variation with depth
ΔP=ρgΔh
What is the standard atmosphere?
The pressure produced by a column of mercury 760mm in height at 0°C under standard gravitational acceleration.
Formula for work done to raise an object
W=mg(z2-z1)
z is about distance.
Kinetic and potential energy definitions
Kinetic: as a result of its motion relative to some reference frame.
Potential: as a result of its elevation in a gravitational field.
What is work?
What is performed whenever a force acts through a distance. The amount performed is dependent on the path taken.
What defines a polytropic system?
When PV=k
What is heat?
The form of energy that is transferred between two systems (or 1 and its surroundings) by virtue of a temperature difference.
What do q, Q and Q• (dot on top) denote?
Q is amount of heat transfer in a given time.
q is heat transfer per unit mass (Q/m).
Q• is heat transfer rate (Q=Q•Δt)
What is an adiabatic system?
A system which exchanges no heat with its surroundings and so is perfectly insulated from them.
