Concepts of Thermodynamics I

Question 1

Forms of energy

Answer 1

1) Potential energy - any form of stored energy
2) Kinetic energy - energy of moving objects

Question 2

What is a System?

Answer 2

System in a flaks, flask is a boundary and surroundings is the enviroment outside

System + surroundings = universe

Question 3

Types of systems

Answer 3

• Isolated system
• Closed system
• Open system

Question 4

Zeroth Law of Thermodynamics

Answer 4

If all are in equilibrium energy can be transferred
Energy transferred from B to C through A
Different pathways

Question 5

First Law of Thermodynamics

Answer 5

“Energy cannot be created or destroyed – it can only be transformed from one form to another”

Question 6

Law of Conservation of Energy

Answer 6

“The change in internal energy of a closed system will be equal to the heat added or released by the system minus the work done by the system on its surrounding or the work done on the system by its surroundings”

Question 7

Equation to first law

Answer 7

AU = Q - W

AU - change in internal energy
Q - Heat added to the system
W - work done by the system

Question 8

Q positive

Answer 8

Heat added to the system
ENDOTHERMIC process

Question 9

Q negative

Answer 9

Heat released from the system
ENDOTHERMIC process

Question 10

Constant Volume (Isovolumeric)

Answer 10

∆U = q
No Work is done on or by the system
Any energy change is result of heat transfer

Question 11

Constant Temperature (Isothermal)

Answer 11

q = w
No change in internal energy
Any heat transferred to the system is used to do work

Question 12

No Heat Transfer (Adiabatic)

Answer 12

Internal energy changes only for work done or received by the system

Question 13

Energy and Heat Capacity

Answer 13

ratio of heat absorbed by a material to the temperature change

Question 14

What are the units of energy?

Answer 14

J - joules (SI units)

Question 15

1 cal

Answer 15

heat needed to raise the temperature of 1 gram of water 1⁰C at standard pressure

Question 16

Conversion of J to cal

Answer 16

1 cal = 4.184 J, 1 kcal = 4184 J

Question 17

Heat Capacity (C):

Answer 17

amount of heat required to raise a substance’s temperature by 1 Kelvin

Question 18

Specific Heat Capacity (Cₛ):

Answer 18

amount of heat required to raise 1 gram of a substance by 1 Kelvin

Question 19

What is Enthalpy?

Answer 19

Enthalpy is the measurement of energy in a thermodynamic system (joules)

Question 20

Equation of enthalpy

Answer 20

∆H = ∆U + ∆(PV)

Question 21

What does each letter mean?
∆H = ∆U + ∆(PV)

Answer 21

P = Pressure, V = Volume
∆H = ∆U and ∆U = q, therefore ∆H = q

Question 22

q > 0, so ∆H is positive

Answer 22

Endothermic process

Question 23

q < 0, so ∆H is negative

Answer 23

Exothermic process

Question 24

2nd Law of Thermodynamics

Answer 24

“The Universe is always moving towards maximum disorder”

Question 25

Entropy (s)

Answer 25

Measure of disorder

Question 26

Breakdown of units of 2nd Law of Thermodynamics

Answer 26

s = KB ln W

KB = Boltzmann constant (energy of an individual atom)

W = microstates (ways to arrange particles in a system)

∆s = sf - si

Question 27

Increase in the number of micro-states
∆s = sf – si

Answer 27

then Wf > Wi and the entropy of the system increases ∆S > 0

Question 28

Decrease in the number of micro-states

Answer 28

then Wf < Wi and the entropy of the system decreases ∆S < 0

Question 29

More micro-states

Answer 29

More disorder

Question 30

Two Bulb Experiment:

Answer 30

Spontaneous process where gas expands to fill
both bulbs equally, increasing entropy

Question 31

More space for gas to go to…

Answer 31

More disorder

Question 32

Wf < Wi

Answer 32

decrease in number of micro states
f = final
i = initial

Question 33

2nd law - Increase Temperature:

Answer 33

Entropy will be greater as molecules have more kinetic energy and therefore more dispersion

Question 34

Change state:

Answer 34

Gas > Liquid > Solid – more dispersion

ENTROPY increase - particles are more free

Question 35

Mixing of particle types:

Answer 35

Increases entropy therefore dissolution increases entropy

Question 36

3rd Law of Thermodynamics

Answer 36

“At absolute zero (0 K), the entropy of a perfect, crystalline substance is zero”

Question 37

Why does entropy equal zero?
3rd Law

Answer 37

All vibrations and atomic movements stop
What temperature is absolute zero in ⁰C?
Answer: -273.15 ⁰C

Comes from the Triple Point of water, T3 = 273.15K

Question 38

CO2 (s) > CO2 (g)

Answer 38

Entropy increase
Solid to gas

Question 39

If there is more molecules of gas than the other side of equation…

Answer 39

the one with more has the higher temperature