Option B2 Flashcards
Thermodynamics
State
The first law of thermodynamics
Define Internal energy
Internal energy is defined as the energy associated with the random, disordered motion of molecules.
should be equal to
Total Potential energy + Random kinetic energy of moleucles
State
The second law of thermodynamics
in Clausius form
It is impossible for thermal energy to flow from a cold to a hot object without performing any work.
State
The second law of thermodynamics
in Kelvin form
It is impossible, in a cyclic process, to completely convert heat into mechanical work.
State
The second law of thermodynamics as a
consequence of Entropy
The total entropy of a system either increase or remain constant, it never decreases.
Formula
of calculating
Change in Internal Energy
Explain
the sign convention of
quantum energy/heat transfer
between a system and its surrounding (Q)
Q > 0 if heat is supplied to the system
Q < 0 if heat is released by the system
What is the formula of
calculating Workdone (W)
in first law of thermodynamic
Explain the sign convention
of Workdone (W) in
the first law of thermodynamic
Describing the first law of thermodynamics as a statement of conservation of energy
What is
Entropy?
Entropy is
A measure of disorder
Describle
how a system will become
more disorder (i.e. entropy increase)?
A system will be more disorder if it is more difficult to determine the position of molecules, e.g.
- Temperature increase
- Volume increase
- No of molecules increase
- Change of stage from Solid to Liquid to Gas
What is the formula
of calculating
Change in Entropy?
What is the entropy change for
Reversible and Inreversible Process
according to the second law of thermodynamic?
·
Under what condition that
A process will have decrease in entropy?
A process with have decrease in entropy
only if energy is supplied
In what way do the entropy
of a universe (or a closed system)
change?
The entropy of a universe (or a closed system) is constantly increasing, never decreasing
When will two systems
are said to be in same state?
Two systems are said to be in same state if they have the same pressure, same volume and same temperature and hence they have the same internal energy.
What is
the Ideal Gas Law?
What is the work done
of the cyclic process AB
In a PV graph?
work done = area within the loop
What does the direction of
a cyclic process indicate?
Characteristics of a
Isochoric or isovolumetric process
Characteristics of a
Isobaric process
Characteristics of
an Isothermal process
Characteristics of
an Adiabatic Process
How to
distinguish between
adiabatic and isothermal curve?
What is the
difference between
Adiabatic Compression
and
Isothermal Compression?
What is a
Carnot cycle ?
The Carnot cycle represents the cycle of processes for a theoretical heat engine with the maximum possible efficiency. Such an idealized engine is called a Carnot engine.
What are the processes
in a Carnot Cycle ?
What is
the Thermal efficiency
for a Carnot engine?
What is
the Thermal efficiency
for a heat engine?
Explain, in terms of the energy of its molecules, why the temperature of a pure substance does not change during melting.
Energy supplied during melting is used to break bond between water molecules, the energy supplied increase potential energy of molecules, and no increase in kinetic energy, so there is no change in temperature.
State what is meant by an isothermal process
An isothermal process is a process in which temperature remains constant
State what is meant by a
Isochoric or isovolumetric process?
Process in which the volume of the system does not change
State what is meant by
an Isobaric process?
Process in which the pressure of the system is constant.
State what is meant by
an Adiabatic Process?
Process in which there is no exchange of thermal energy between a system and it surroundings.
Explain why it is not possible for an engine, operating in a cycle, to be 100% efficient
For an engine to be operating in a cycle, the system must return to original conditions (P, V, and T), to do that, some of the thermal energy absorbed by gas must be given off to the surroundings; hence not all thermal energy absorbed by gas can be converted to work; it is the second law of thermodynamics;
Describe how the ideal gas constant R is defined.
With respect to a gas, explain the meaning of the terms thermal energy and internal energy
Thermal energy (Q) is the energy transferred between two objects when are at different temperatures.
Internal energy (U) is the energy associated with the random, disordered motion of molecules, which comprises of the total potential energy and random kinetic energy of the molecules of the gas.
Outline why an efficiency calculation is important for an engineer designing a heat engine.
So as to reduce energy loss; increase engine performance; effective use of fuel; etc.
There are various equivalent versions of the second law of thermodynamics. Outline the benefit gained by having alternative forms of a law.
There are different modellings, allow testing in different ways and the laws can be applied in different situations.
Define Thermal Energy
Energy transferred between two objects which are at different temperature
