WEEK 5 (Thermodynamics II) Flashcards
In Isobaric processes what is the constant?
Pressure
In Isothermal processes what is the constant?
Temperature
In Isovolumetric processes what is the constant?
Volume
What is an Adiabatic process?
An adiabatic process is defined as a process in which no heat transfer takes place. This does not mean that the temperature is constant, but rather that no heat is transferred into or out from the system.
What is an Isobaric process?
An isobaric process is a process occurring at constant pressure. The first law of thermodynamic equation for the isobaric process remains the same as the pressure remains constant and because of the volume change, the system does work.
What is an Isothermal process?
An isothermal process is a thermodynamic process in which the temperature of a system remains constant. The transfer of heat into or out of the system happens so slowly that thermal equilibrium is maintained
A gas undergoes a thermodynamic process. During this process, no work is done. Which of the following is the best description of the process?
Isovolumetric process
In a thermodynamic process no heat is transferred. What is the best description of the process?
Adiabatic process
What is the first law of thermodynamics?
Energy cannot be created or destroyed, but it can be transferred.
What is important about reversible and irreversible processes?
- in reversible processes every state of a system is in equilibrium state
- if any state of a system is not in equilibrium state it is an irreversible process
- reversible processes is the ideal
- most natural processes are irreversible
What is the second law of thermodynamics?
The second law of thermodynamics states that as energy is transferred or transformed, more and more of it is wasted.
Therefore, no heat engine operating in a cycle can absorb energy from a reservoir and use it entirely for the performance of an equal amount of work.
Why do all real engines work irreversibly?
Due to friction and brevity of cycles
When is ec maximal in the equation for the second law of thermodynamics?
when Tc=0K
When Tc=0K this causes Tc/Th to equal 0 (1-0=1) therefore ec will remain to be 1 which is the maximum
What is the history behind the idea of Entropy?
- developed by Rudolf Clausius in the mid-1800s
- efficiency of heat engines were about 1%; he tried to understand the reason to quantitatively account heat loss
- he called the lost heat the “equivalence value of all uncompensated transformations” (amount of heat that could not be compensated for by transforming the resulting work back to the heat)
- he introduced the work “entropy”
What is the equation for entropy?
ΔS = Q/T J/K
S is an entropy, Q – heat irreversibly lost in surroundings, T – absolute temperature
What is the direction of spontaneous change in a system directed to?
To form an arrangement of lesser probability (ordered) to an arrangement of greater probability (random)
What are the key points from the second law of thermodynamics?
- heat spontaneously flows from a place of higher temperature to a place of lower temperature
- when converting energy into work, some of the energy is always lost to heat
- in any process, the entropy of a closed system and an open system will either increase or remain constant
- in any process, a system taken together with its surroundings will always go from a more ordered state to a less ordered state
- entropy of the universe increases in all natural processes
- second law of thermodynamics is a statement of what is most probable than what must be
In spontaneous processes, Gibbs free energy is always ___________
negative
In human metabolism, is energy change always positive or negative?
Negative
Animals take this energy from food and breathing
What is metabolic rate?
Metabolic rate is the rate at which chemical potential energy in food and oxygen are transformed into internal energy to balance the body losses of internal energy by work and heat
What is metabolic rate directly proportional to?
The rate of oxygen consumption by volume
in an average diet, how much energy does the consumption of one litre of oxygen release?
4.8 kcal or 20 kJ of energy
