The Second Law of Thermodynamics Flashcards
How is the first law of thermodynamics satisfied with a cup of tea?
the heat energy is transferred from the tea to the surrounding air and the total energy remains constant
If a process satisfies the first law, will it definitely occur?
no, as the first law doesn’t define direction
What has to happen for a process to occur?
the process has to obey the first and second law of thermodynamics
What is the more valuable form of energy, heat or work?
work
How can we convert heat into work?
by using a heat engine
What characteristics do heat engines have?
*they receive heat from a high temperature source
*they convert part of this heat into work
*they reject the remaining heat as waste to a low temperature sink
*they operate on a cycle
What is a cycle?
*a sequence of processes that begin and end at the same state
*all properties have the same values that they had at the beginning of the cycle
What is still true about heat and work in a cycle?
work and heat are not process dependent so
Qnet = Wnet
Is there enthalpy or internal energy in a cycle?
delta H and delta U are zero
What can be said about Qout for a thermodynamic cycle?
*Qout can never be zero
*the net work output is always less than the heat input
What is thermal efficiency?
the fraction of heat input that is converted to net work output is a measure of the engine performance
What is the limitation for thermal efficiency?
it will always be less than 100%
What is the second law of thermodynamics?
it is impossible for any device that operates on a cycle to receive heat from a single reservoir and produce an equivalent amount of work
What is a reversible process?
a process which can be reversed without leaving any effect on the surroundings
What causes an irreversible reaction?
*friction
*unrestrained expansion
*mixing of two gases
*heat transfer across a finite temp difference
*electrical resistance
*inelastic deformation of solids
*chemical reactions
