The First Law of Thermodynamics Flashcards
What is Thermodynamics
Is the study of the way different types of energy interconver
Thermodynamics divides the world into two parts: they System and the Surroundings
What is the difference between the two
System: the part of the world we want to study
Surroundings: the rest of the world outside the system
We can only measure energy as
A change in the energy of a system
This can be achieved by observing its transfer to and from the surroundings
What is an open system
A system in which both matter and energy can be exchanged with the surroundings
For example: a reaction taking place in a beaker is an open system
What is a closed system?
A system that contains fixed amount of matter but allows the exchange of energy
For example: a sealed reaction vessels holds all the content in but heat can be conducted
What is an isolated system?
A system where there can be no exchange of energy or matter with the surroundings
For example: a sealed, well-insulated vaccum flask
What is energy
Energy can be thought of as the capacity to do work
What is work
Work is done when moving against a force
What is the equation for Work Done
w = Fs
w = work done (J)
F = Force (N)
s = distance (m)
What is Internal Energy (U)
The total capacity of a system to do work
What is an ideal gas
There are no forces between the molecules
How do internal energy and ideal gases related
- Ideal gases have no intermolecular potential energy
- The internal energy of an ideal gas is purely kinetic and therefore depend only on temperature
- The internal energy of an ideal gas is independent of volume
What is the First Law of thermodynamics
Energy can neither be created nor destroyed BUT is just transferred from one form into another
What happens to the internal energy of a system if work is doen
Internal energy decreases
What happens to the internal energy of a system, if work is done to it
Its internal energy increases
How does Work and Heat related to an isolated system
No work can be done on or by an isolated system
No heat flows to or from and isolated system
How can the internal energy of a system be changed
By transferring energy to or from the system as heat
Describe the movement of heat
Heat is energy which flows from high-temperature objects to low-temperature ones
What is thermal equilibrium
Objects at the same temperature are in thermal equilibrium, meaning there is no net heat flow between them
(Zeroth law of thermodynamics)
What is Molar Heat Capacity (C) of a substance
What is its units
- is a measure of how much heat must be supplied to raise its temperature by 1K
- Units = J mol⁻¹ K⁻¹
What is the equation used to work out the amount of heat supplied (J) relating to the Molar Heat Capacity (J mol⁻¹ K⁻¹)
q = nCΔT
q = amount of heat supplied (J)
n = amount of substance (mol)
C = molar heat capacity ( J mol⁻¹ K⁻¹)
ΔT = change in temp (K)
For gases, the value of heat capacity depend on wheather the measurements are carried out under which two conditions
- Constant pressure (Cp)
- Constant Volume (Cv)
The heat capacity of a particular substance is related to the number of degrees of freedom possessed by its molecules
How?
As the molecules become more complex there are more degrees of freedom which can absorb the heat
Hence have a higher Heat Capacity (C)
A system can do two kinds of work: expansion and non-expansion
What is the difference
Expansion: work involved a change in the volume of the system, such as the work done by a reaction with gaseous products
Non-expansion: work does not involved a change in volume, such as the electrical work done by the reaction in a battery
