engineering- thermodynamics

Question 1

what is the Kelvin scale?

Answer 1

the absolute temperature scale

Question 2

how do you calculate kelvin from degrees celcius?

Answer 2

add 273

Question 3

what is Boyle’s law?

Answer 3

the pressure of a gas is inversely proportional to the volume

Question 4

what is Charles’ law?

Answer 4

the volume occupied by a gas is proportional to its absolute temperature

Question 5

what is the pressure law?

Answer 5

pressure of a gas is proportional to its absolute temperature

Question 6

what is x?
p ∝ 1/x

Answer 6

V

Question 7

what is x?
V ∝ x

Answer 7

T (or 1/p)

Question 8

what law states p ∝ 1/V

Answer 8

Boyle’s law

Question 9

for the pressure law, what is x?
p ∝ x

Answer 9

T

Question 10

what is the ideal gas law?

Answer 10

pV = nRT

Question 11

what equation links number of moles and number of molecules?

Answer 11

number of moles = number of molecules / avogadro’s constant

n = N/ NA

Question 12

what are 5 assumptions made when modelling an ideal gas?

Answer 12

1. its made of tiny spheres
2. the spheres obey Newton’s laws of motion
3. they occupy a negligible space in comparison with the volume occupied by the gas
4. the spheres don’t exert non-contact forces on one another
5. collisions involving the spheres are totally elastic

Question 13

what is the first law of thermodynamics?

Answer 13

Q = ∆U + W
heat energy = internal energy + work done

Question 14

what is the symbol for heat energy?

Answer 14

Q

Question 15

what is the symbol for internal energy?

Answer 15

∆U

Question 16

what is the symbol for work done?

Answer 16

W

Question 17

which 3 ways can energy change in a closed system?

Answer 17

1. heat energy can enter or leave
2. work can be done on or by the system
3. internal energy store of the system can increase or decrease

Question 18

what has happened when a system expands?

Answer 18

work is done BY the system

Question 19

what has happened when temperature decreases?

Answer 19

particles lose energy

Question 20

when is the value for heat positive?

Answer 20

when heat goes into the system

Question 21

what happens when work is done on the system?

Answer 21

it is compressed

Question 22

what is constant during an isothermal process?

Answer 22

∆U = 0

Question 23

in which non-flow process does the temperature stay the same?

Answer 23

isothermal

Question 24

what does adiabatic mean?

Answer 24

without the transfer of heat

Question 24

what happens in an adiabatic process?

Answer 24

no heat is gained or lost by the system

Question 24

what does the 1st law of thermodynamics become for an adiabatic procces?

Answer 24

∆U = -W or 0 = ∆U + W

Question 24

in which non-flow process is Q = 0

Answer 24

adiabatic

Question 25

what happens to the ideal gas equation for an isothermal process?

Answer 25

pV = constant constant = pV = nRT

Question 26

what has happened when a gas expands?

Answer 26

work has been done by the gas

Question 27

what does the 1st law of thermodynamics become for a constant volume process?

Answer 27

Q = ∆U

Question 28

which process has the equation: work done, W = p∆V

Answer 28

constant pressure processes

Question 29

what does γ (gamma) represent?

Answer 29

(DF + 2) / DF DF= number of degrees of freedom

Question 30

does an isothermal or adiabatic change have a steeper curve on a P/V graph?

Answer 30

adiabatic

Question 31

which process moves from one isotherm to another on a P/V graph?

Answer 31

adiabatic change

Question 32

what does the area under a graph show on a p/v graph?

Answer 32

work done

Question 33

in what process is pV^γ = constant?

Answer 33

adiabatic

Question 34

what is constant in an isothermal process?

Answer 34

pV

Question 35

which way does the arrow point on a P/v graph for an expansion?

Answer 35

right

Question 36

which way does the arrow point on a P/v graph for a compression?

Answer 36

left

Question 37

which is happening to a gas if the arrow on a p/v graph is pointing right?

Answer 37

expansion

Question 38

what =0 when the arrow on a p/v graph goes straight up or down?

Answer 38

W = 0 because its a constant volume process

Question 39

how do you find work done per cycle on a p/v graph?

Answer 39

area inside the loop

Question 40

what does it mean if a process is non-flow?

Answer 40

it occurs in a closed system no fluid is added or lost in the process they are reversible

Question 41

what are 4 non-flow processes?

Answer 41

isothermal constant pressure constant volume adiabatic

Question 42

what is an isothermal change?

Answer 42

a change that occurs at a constant temperature internal energy stays constant so Q = W meaning any transfer of energy would lead to work being done and vice versa

Question 43

what law does an isothermal change obey?

Answer 43

Boyle's law

Question 44

if work is done by the system in an adiabatic change, what will happen to the internal energy?

Answer 44

it will decrease

Question 45

what =0 in a constant volume change? ( Q, U or W )

Answer 45

W = 0

Question 46

what does a graph of 'constant volume' change for heating on a p/v diagram look like?

Answer 46

arrow pointing straight up as temperature has increase no work done as volume doesn't change

Question 47

what are indicator diagrams and what are they used for?

Answer 47

a p/v diagram for engines that allows identification of the different processes in the system

Question 48

what are the basics of the four stroke petrol engine cycle?

Answer 48

piston moves down in the cylinder increasing the volume of gas above it, air and petrol vapour are drawn into the cylinder through the open inlet valve, pressure stays constant, volume increases