Слайд 2Learning Objectives
understand and apply first law of thermodynamics
distinguish graphs of
adiabatic and isothermal processes
understand second law of thermodynamics
Слайд 3Terms to Remember!
Thermodynamics
Thermodynamic System
Surroundings
Heat
Work
Internal Energy
Слайд 4Thermodynamics
Thermodynamics is the macroscopic study of the behaviour of systems.
It was a mathematical theory developed before a detailed understanding
of the particulate nature of gases.
Слайд 5Thermodynamic System
Thermodynamic System is a macroscopic aspect of a problem
than can be considered as a separate whole. An ideal
gas for example can have energy flowing in or out of it from
the surroundings.
Слайд 6Surroundings
Surroundings is everything in the problem outside the
thermodynamic system.
Heat can flow from the system to the surroundings and
vice versa.
Слайд 12Heat
Heat (Q) is an amount of thermal energy transferred from
the surroundings to an ideal gas. It is a result
of a temperature difference.
Слайд 14Work
Work (W) is simply a macroscopic transfer of energy from
the gas to the surroundings.
Слайд 21Change in Internal Energy
Change in Internal Energy (∆U) is the
change in a gas’ energy due to the PE and
KE of the molecules.
It does not include external factors such as gravity.
∆U for an ideal gas will involve temperature changes (∆θ).
Слайд 22Change in Internal Energy
The change in internal energy (ΔU) of
a closed system will be equal to the energy added
to the system by heating minus the work done by the system on the surroundings.
ΔU = Q – W
Слайд 231st Law of Thermodynamics
The First Law of Thermodynamics states that
when heat Q is added to a system while the
system does work W, the internal energy U changes by an amount equal to Q – W.
ΔU = Q – W
Слайд 241st Law of Thermodynamics
Since Q and W represent energy transferred
into or out of the system , the internal energy
changes accordingly.
The First Law of Thermodynamics is great and broad statement of the law of conservation of energy.
Слайд 251st Law of Thermodynamics
The internal energy of any thermodynamic system
depends only on its state. The change in internal energy
in any process depends only on the initial and final states, not on the path.
The internal energy of an isolated system is constant.
Слайд 26State
State is defined as the physical condition of the system.
Слайд 27Important Note
A given system at any moment is in particular
state and can be said to have a certain amount
of internal energy.
But a system does NOT have a certain amount of heat or work.
Слайд 28Important Note
Rather, when work is done on a system or
when heat is added or removed from a system, the
state of the system changes.
Слайд 29Important Note
Thus, work and heat are involved in thermodynamic processes
that can change the system from one state to another;
they are not characteristic of the state itself.
Слайд 30State Variables
Quantities which describe the state of the system is
called state variables.
Internal Energy (U) Mass (m)
Pressure (P) Volume (V)
Temperature (T)
Number of Moles (n)
Слайд 31Sample Problem
2500 J of heat is added to a system,
and 1800 J of work is done on the system.
What is the change in internal energy of the system?
Слайд 32Sample Problem
2500 J of heat is added to a system,
and 1800 J of work is done by the system.
What is the change in internal energy of the system?