Chapter 2: Energy & energy transfer

Question 1

what can energy cause?

Answer 1

it can cause change and work

Question 2

what are macroscopic forms of energy?

Answer 2

those a system possesses as a whole with respect to some outside reference frame, such as kinetic and potential energy

Question 3

what are microscopic forms of energy?

Answer 3

related to the molecular structure of a system and the degree of the molecular activity

Question 4

what is kinetic energy?

Answer 4

the energy a system possesses as a result of its motion relative to some reference frame

Question 5

what is potential energy?

Answer 5

the energy that a system possesses as a result of its elevation in a gravitational field

Question 6

what is internal energy?

Answer 6

Sum of all microscopic forms of energy, it comes from the total kinetic (changes with temperature) and potential energy (changes with state) of molecules which composes the system

Internal = thermal + chemical + nuclear + electric + magnetic

Internal = sensible + latent + chemical + nuclear

Question 7

what is sensible energy?

Answer 7

portion of internal energy of a system associated with the kinetic energies of the molecules

Question 8

what is latent energy?

Answer 8

portion of internal energy associated with the phase of a system

Question 9

what is chemical energy?

Answer 9

portion of internal energy associated with the atomic bonds in a molecule

Question 10

what is nuclear energy?

Answer 10

portion of internal energy associated with the strong bonds within the nucleus of the atom itself

Question 11

what is thermal energy?

Answer 11

thermal = sensible + latent

Question 12

what is a stationary system?

Answer 12

where total energy = total internal energy
since both kinetic and potential energy are equal to zero

Question 13

what is mechanical energy?

Answer 13

form of energy that can be converted to mechanical work completely and directly by an ideal mechanical device, such as an ideal turbine

Question 14

what is the mechanical flow energy of a flowing fluid?

Answer 14

pressure

Question 15

where does total energy occur when in static form?

Answer 15

contained or stored in a system

Question 16

where does energy interactions occur when in dynamic forms?

Answer 16

at the system boundary

Question 17

what kind of systems can heat transfer occur in?

Answer 17

closed and open systems

Question 18

what kind of systems can work occur in?

Answer 18

closed and open systems

Question 19

what kind of systems can mass transfers occur in?

Answer 19

open systems only

Question 20

what is heat and when does heat transfer occur?

Answer 20

heat is a form of energy that is transferred between 2 systems or between a system and its surrounding when there is a difference in temperature between them
no temperature difference = no heat transfer

Question 21

what is conduction?

Answer 21

heat transfer mechanisms that transfers energy from the more energetic particles of a substance to the adjacent less energetic ones as a result of interaction between particles (touching)

Question 22

what is convection?

Answer 22

heat transfer mechanism that transfers energy between a solid surface and the adjacent fluid that is in motion.
Involves the combined effects of conduction and fluid motion: the faster the fluid motion the greater the heat transfer

Question 23

what is radiation?

Answer 23

heat transfer mechanism that transfers energy due to the emission of electromagnetic waves (or photons)

Question 24

when is energy recognized as heat transfer?

Answer 24

only when it crosses the system boundary

Question 25

what is work?

Answer 25

the energy transfer associated with a force acting through a distance. the energy transfer is not due to temperature differences the work done is proportional to the force applied and the distance traveled.

Question 26

what is mechanical work?

Answer 26

work due to the transfer of mechanical energy work done to raise and/or accelerate a body = change in potential and/or kinetic energy

Question 27

what are the conditions for mechanical work to occur?

Answer 27

1. A force is acting on the boundary of the system 2. The boundary must move both conditions need to be met for work to be done

Question 28

what are examples of different forms of mechanical work?

Answer 28

- Shaft work: force acting through a moment arm generates a torque, this forced acts through a distance - Spring work: length of spring changes under influence of a force - Elastic solid bars work: without permanent deformation, normal stress - Stretching of a liquid film work: surface tension - work done to raise or accelerate body = related to potential and kinetic energy

Question 29

what is electrical work?

Answer 29

non-mechanical form of work where the generalized force is the volt (electric potential) and the generalized displacement is the electrical charge

Question 30

what is magnetic work?

Answer 30

non-mechanical form of work where the force is the magnetic field strength and the displacement is the total magnetic dipole moment

Question 31

what is electrical polarization work?

Answer 31

non-mechanical form of work where the force is the electrical field strength and displacement is the polarization of the medium

Question 32

What kind of functions are heat and work?

Answer 32

path functions, they both are associated with process and their magnitudes depend on the path followed during a process as well as the end states - they have inexact differentials

Question 33

what kind of functions are properties?

Answer 33

point functions, associated with state - exact differentials

Question 34

difference between energy transfer in a closed vs open system?

Answer 34

In a closed system, only heat transfer and work are included in energy transfer In an open system, energy transfer also include the flow energy in addition to work and heat

Question 35

what is the zeroth law of thermodynamics?

Answer 35

If object A is in thermal equilibrium with object B, and object B is in thermal equilibrium with object C, then object C is also in thermal equilibrium with object A

Question 36

what is the first law of thermodynamics?

Answer 36

energy can be neither created nor destroyed during a process, it can only change forms - total energy remains constant

Question 37

what is the sign convention for heat transfer to a system and work done on a system?

Answer 37

positive

Question 38

what is the sign convention for heat transfer from a system and work done by a system?

Answer 38

negative

Question 39

what does a closed system cycle involve?

Answer 39

only heat transfer and work total energy = 0, so Q = W

Question 40

what is energy efficiency?

Answer 40

performance of energy conversion or transfer process - losses are due to friction or heat - increased energy efficiency = reduced energy use

Question 41

what is energy efficiency?

Answer 41

performance of energy conversion or transfer process - losses are due to friction or heat - increased energy efficiency = reduced energy use

Question 42

what is pump and turbine efficiency?

Answer 42

the effectiveness of the conversion process between the mechanical work supplied or extracted and the mechanical energy of the fluid

Question 43

what is pump and turbine efficiency?

Answer 43

the effectiveness of the conversion process between the mechanical work supplied or extracted and the mechanical energy of the fluid