Thermodynamics- First Law

Question 1

What is equilibrium in a system?

Answer 1

When there are no unbalanced potentials (or driving forces) within the system.

Question 2

What are thermal, mechanical, phase and chemical equilibria?

Answer 2

Thermal: temperature is the same throughout the entire system.
Mechanical: no change in pressure at any point of the system with time.
Phase: if a system involves 2 phases and the mass of each phase reaches a constant level.
Chemical: chemical composition of system doesn’t change with time (no tendency for reaction).

Question 3

What does the state postulate say?

Answer 3

The state of a simple compressible system is completely specified by two independent, intensive properties.

Question 4

What is a simple compressible system?

Answer 4

A system involving no electrical, magnetic, gravitational, motion and surface tension effects.

Question 5

What is Gibbs phase rule?

Answer 5

The number of the independent intensive properties needed to constrain the properties in a given phase is given by:
F=C-P+2
F is number of properties (degrees of freedom)
C is number of components in the system (not dependent on phase)
P is the number of phases present in the system

Question 6

What is a process?

Answer 6

Any change that a system undergoes from one equilibrium to another.

Question 7

What is a path?

Answer 7

The series of states through which a system passes during a process.

Question 8

How to describe a process completely

Answer 8

Specify the initial and final states, as well as the path the system follows and the interactions with the surroundings.

Question 9

What is a quasi-equilibrium process?

Answer 9

When a process proceeds in such a manner that the system remains infinitesimally close to an equilibrium state at all times, e.g a gradual compression.

Question 10

Define the processes isothermal, isobaric, isochoric (isometric) and define a cycle

Answer 10

Isothermal: constant temperature
Isobaric: constant pressure
Isochoric (isometric): constant volume with constant mass
Cycle: a process in which the initial and final states are identical (not always the same paths taken though)

Question 11

Define and describe a steady flow process

Answer 11

A process during which a fluid flows through a control volume steadily. So the fluid properties can change from point to point but at any fixed point, they remain the same during the entire process.

Question 12

Define steady and uniform

Answer 12

Steady: implies no change with time
Uniform: implies no change with location over a specified region

Question 13

What is internal energy

Answer 13

The sum of all the microscopic forms of energy of a system and can be viewed as the sum of the kinetic and potential energies of the molecules.

Question 14

What is mechanical energy?

Answer 14

The form of energy that can be converted to mechanical work completely and directly by an ideal mechanical device. It includes kinetic and potential energies.

Question 15

What is the total energy contained or stored by a system equivalent to?

Answer 15

Internal energy + kinetic energy + potential energy

Question 16

What are dynamic forms of energy?

Answer 16

The forms of energy not stored in a system. They cross the boundary and represent the energy gained or lost by a system during a process.

Question 17

What is sensible energy?

Answer 17

The portion of the internal energy of a system associated with the (microscopic) kinetic energies of the molecules.

Question 18

What is chemical energy?

Answer 18

The internal energy associated with the atomic bonds in a molecule

Question 19

Latent energy

Answer 19

The internal energy associated with the phase of the system

Question 20

Nuclear energy

Answer 20

The tremendous amount of energy associated with the strong bonds within the nucleus of the atom itself.

Question 21

First law of thermodynamics

Answer 21

Energy cannot be created or destroyed during a process, it can only change forms

Question 22

What is a stationary system?

Answer 22

Where there is no change in kinetic or potential energy. So the total change in energy of the system is equal to the change in internal energy.

Question 23

What are the different mechanisms of energy transfer?

Answer 23

Heat transfer, work transfer, flow of mass

Question 24

Graph of pressure against volume for compression or expansion of fluid.

Answer 24

Curved line down with increasing gradient (getting less -ve)

Question 25

Work done to compress a fluid is given on a PV graph by…

Answer 25

The area under the curve between the initial and final volumes.

Question 26

What is the change of internal energy of a compressing fluid equal to?

Answer 26

The change in heat energy - the work done. Be careful with whether these energies are positive or negative

Question 27

What is cv?

Answer 27

v is subscript. Specific heat at constant volume. The energy required to raise the temperature of the unit mass of the a substance by 1°C as the volume is maintained constant. Also is the change in internal energy with temperature at constant volume.
cv=(δu/δT)

Question 28

What is cp?

Answer 28

p is subscript. Specific heat at constant pressure. The energy required to raise the temperature of the unit mass of a substance by 1°C as the pressure is maintained constant. Also the change in enthalpy with temperature at constant pressure.
cp=(δh/δT)

Question 29

What is an incompressible substance?

Answer 29

A substance whose specific volume or density is constant. Like solids and liquids.

Question 30

What is the formula for enthalpy?

Answer 30

Internal energy + pressure times volume

Question 31

What is the specific heat ratio?

Answer 31

Symbol k. cp over cv

Question 32

For an ideal gas what values are a function of temperature only?

Answer 32

Enthalpy and internal energy