WEEK 5 (Thermodynamics II)

Question 1

In Isobaric processes what is the constant?

Answer 1

Pressure

Question 2

In Isothermal processes what is the constant?

Answer 2

Temperature

Question 3

In Isovolumetric processes what is the constant?

Answer 3

Volume

Question 4

What is an Adiabatic process?

Answer 4

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.

Question 5

What is an Isobaric process?

Answer 5

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.

Question 6

What is an Isothermal process?

Answer 6

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

Question 7

A gas undergoes a thermodynamic process. During this process, no work is done. Which of the following is the best description of the process?

Answer 7

Isovolumetric process

Question 8

In a thermodynamic process no heat is transferred. What is the best description of the process?

Answer 8

Adiabatic process

Question 9

What is the first law of thermodynamics?

Answer 9

Energy cannot be created or destroyed, but it can be transferred.

Question 10

What is important about reversible and irreversible processes?

Answer 10

• 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

Question 11

What is the second law of thermodynamics?

Answer 11

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.

Question 12

Why do all real engines work irreversibly?

Answer 12

Due to friction and brevity of cycles

Question 13

When is ec maximal in the equation for the second law of thermodynamics?

Answer 13

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

Question 14

What is the history behind the idea of Entropy?

Answer 14

• 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”

Question 15

What is the equation for entropy?

Answer 15

ΔS = Q/T J/K

S is an entropy, Q – heat irreversibly lost in surroundings, T – absolute temperature

Question 16

What is the direction of spontaneous change in a system directed to?

Answer 16

To form an arrangement of lesser probability (ordered) to an arrangement of greater probability (random)

Question 17

What are the key points from the second law of thermodynamics?

Answer 17

• 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

Question 18

In spontaneous processes, Gibbs free energy is always ___________

Answer 18

negative

Question 19

In human metabolism, is energy change always positive or negative?

Answer 19

Negative

Animals take this energy from food and breathing

Question 20

What is metabolic rate?

Answer 20

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

Question 21

What is metabolic rate directly proportional to?

Answer 21

The rate of oxygen consumption by volume

Question 22

in an average diet, how much energy does the consumption of one litre of oxygen release?

Answer 22

4.8 kcal or 20 kJ of energy