Lecture 4 (Thermodynamics)

Question 1

What is Thermodynamics?

Answer 1

The study of the relationship between heat, work and the associated flow of energy

Question 2

What is the first law of thermodynamics?

Answer 2

One form of energy can be converted into another, but energy can neither be created nor destroyed

Question 3

What is the second law of thermodynamics?

Answer 3

Spontaneous change in nature occurs from a state of order to a state of disorder

Question 4

Which equation shows that matter and energy are equivalent?

Answer 4

Einstein equation

E = mc^2

E = Energy
M = Mass
C = Velocity of light

Question 5

What is the equation to calculate the change of energy in a system?

Answer 5

ΔEsys = Ein - Eout

Question 6

What is the equation of the first law of thermodynamics?

Answer 6

ΔU = q – w

U = Internal energy of a system
Q = Heat put into the system
W = Work done by the system

Question 7

What is the difference between an Open system, Closed system and an Adiabatic system?

Answer 7

Open system = can exchange both matter and energy with its surroundings

Closed system = can exchange energy but not matter

Adiabatic system = thermally isolated from its surroundings so there is no exchange of heat or matter but its possible for the system to do work on its surroundings

Question 8

Describe an “isolated” system

Answer 8

• no exchange of matter
• no exchange of heat

Question 9

What is energy?

Answer 9

Energy is the capacity of a physical system to perform work

Question 10

What is work?

Answer 10

The measure of energy conversion from one form to another

Question 11

What is the internal energy of the system?

Answer 11

The sum of all forms of energy of this system

Question 12

What are the different types of energy?

Answer 12

• MECHANICAL ENERGY = results from movement or the location of an object (sum of kinetic + potential energy)
• THERMAL ENERGY = temperature difference between two systems
• NUCLEAR ENERGY = resulting from changes in the atomic nuclei or from nuclear
• CHEMICAL ENERGY = results from chemical reactions between atoms or molecules
• ELECTROMAGNETIC ENERGY = energy from light or electromagnetic waves

Question 13

Why is heat special?

Answer 13

• The laws and equations of thermodynamics were originally developed through the study of heat engines
• Heat is the only type of energy that is always readily available to measure and possibly use
• Heat is the least organised form of energy

Question 14

What is the distinction between heat and work?

Answer 14

In work the energy is an ordered motion but in heat the energy is in random motion

Question 15

How do you calculate the total energy consumption per hour?

Answer 15

Multiply metabolic rate by the surface area of the person

Question 16

What is Enthalpy?

Answer 16

Total kinetic and potential energy of a system at a constant pressure

Question 17

What is a Change in Enthalpy?

Answer 17

Change in heat of a system

Question 18

What is the equation to calculate Enthalpy?

Answer 18

H = U + PV

The sum of the internal energy of a system plus its pressure times volume

Question 19

Describe Exothermic reactions

Answer 19

• System loses energy
• Surroundings gain energy
• Surroundings feel warmer
• ΔH is -ve
• Energy value on right of equation (product)
• Potential energy decreases

Question 20

Describe Endothermic reactions

Answer 20

• System gains energy
• Surroundings lose energy
• Surroundings feel colder
• ΔH is +ve
• Energy value on left of equation (reactant)
• Potential energy increases

Question 21

What is the equation to calculate Entropy?

Answer 21

ΔS = Q/T

ΔS = Entropy
Q = Heat irreversibly lost to the surroundings
T = Temperature

Question 22

What is the equation to calculate Entropy when passing the heat through a working body?

Answer 22

ΔS = Q (1/T2 - 1/T1)

Question 23

What is Entropy?

Answer 23

A measure of disorder in a system

[the more ways there are for a system to do one particular thing or to be in one particular state, the more disorder and the more entropy the system has]

Question 24

What is Gibbs free energy and how do you calculate it?

Answer 24

The energy that is free to do useful work

G = H - TS
G = Gibbs energy
H = Enthalpy
T = Temperature
S = Entropy

Question 25

What happens when a process happens spontaneously?

Answer 25

Gibbs energy always decreases -> ΔG is -ve

Question 26

What can contribute to negative ΔG?

Answer 26

• Releasing energy
• Increasing disorder
• Changing temperature

Question 27

What are the flaws of the First law of Thermodynamics?

Answer 27

• It never states under which circumstances and to what extent it is possible to convert one form of energy into another
• It never states that heat has to flow spontaneously from the hotter to the colder body and not in the reverse direction