Lecture 4 (Thermodynamics) Flashcards
What is Thermodynamics?
The study of the relationship between heat, work and the associated flow of energy
What is the first law of thermodynamics?
One form of energy can be converted into another, but energy can neither be created nor destroyed
What is the second law of thermodynamics?
Spontaneous change in nature occurs from a state of order to a state of disorder
Which equation shows that matter and energy are equivalent?
Einstein equation
E = mc^2
E = Energy
M = Mass
C = Velocity of light
What is the equation to calculate the change of energy in a system?
ΔEsys = Ein - Eout
What is the equation of the first law of thermodynamics?
ΔU = q – w
U = Internal energy of a system
Q = Heat put into the system
W = Work done by the system
What is the difference between an Open system, Closed system and an Adiabatic system?
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
Describe an “isolated” system
- no exchange of matter
- no exchange of heat
What is energy?
Energy is the capacity of a physical system to perform work
What is work?
The measure of energy conversion from one form to another
What is the internal energy of the system?
The sum of all forms of energy of this system
What are the different types of energy?
- 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
Why is heat special?
- 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
What is the distinction between heat and work?
In work the energy is an ordered motion but in heat the energy is in random motion
How do you calculate the total energy consumption per hour?
Multiply metabolic rate by the surface area of the person
What is Enthalpy?
Total kinetic and potential energy of a system at a constant pressure
What is a Change in Enthalpy?
Change in heat of a system
What is the equation to calculate Enthalpy?
H = U + PV
The sum of the internal energy of a system plus its pressure times volume
Describe Exothermic reactions
- System loses energy
- Surroundings gain energy
- Surroundings feel warmer
- ΔH is -ve
- Energy value on right of equation (product)
- Potential energy decreases
Describe Endothermic reactions
- System gains energy
- Surroundings lose energy
- Surroundings feel colder
- ΔH is +ve
- Energy value on left of equation (reactant)
- Potential energy increases
What is the equation to calculate Entropy?
ΔS = Q/T
ΔS = Entropy
Q = Heat irreversibly lost to the surroundings
T = Temperature
What is the equation to calculate Entropy when passing the heat through a working body?
ΔS = Q (1/T2 - 1/T1)
What is Entropy?
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]
What is Gibbs free energy and how do you calculate it?
The energy that is free to do useful work
G = H - TS
G = Gibbs energy
H = Enthalpy
T = Temperature
S = Entropy
What happens when a process happens spontaneously?
Gibbs energy always decreases -> ΔG is -ve
What can contribute to negative ΔG?
- Releasing energy
- Increasing disorder
- Changing temperature
What are the flaws of the First law of Thermodynamics?
- 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
