10TH GRADE · THERMODYNAMICS
Internal energy and the first law
Internal energy of a monatomic gas, work and the first law of thermodynamics.
The entire theory of the lesson is collected here; you can read it without an account. In interactive mode, the same theory appears as cards, followed by questions. with checking the answer and task, and progress is saved.
Basic Concepts
Internal energy
Energy of thermal motion and interaction of particles of the system.
This is the energy within the system, and not the energy of its movement as a whole. For an ideal gas it is determined by temperature.
First law of thermodynamics
The law of conservation of energy for thermal processes, connecting heat, internal energy and work.
The heat received by the system is used to change internal energy and to work; It is important to choose and follow a sign convention in advance.
Physical quantities
Internal energy
Total energy of thermal motion and interaction of particles.
Unit: joule ·
Change in internal energy
The difference in internal energy in the final and initial states.
Unit: joule ·
Gas work
Energy transferred by a gas to surrounding bodies during expansion.
Unit: joule ·
Work of external forces
Work of surrounding bodies on gas.
Unit: joule ·
Heat
Energy transferred during heat exchange.
Unit: joule ·
Volume change
The difference between the final and initial volumes.
Unit: cubic meter ·
Temperature change
The difference between the final and initial absolute temperatures.
Unit: kelvin ·
Lesson formulas
Internal energy of a monatomic ideal gas
The internal energy of a monatomic ideal gas is determined by temperature or the product of pressure and volume.
Gas work at constant pressure
In isobaric expansion, work is equal to pressure times change in volume.
Condition: The pressure is constant.
Change in internal energy of gas
The change in internal energy of a monatomic ideal gas is proportional to the change in temperature.
The first law through the work of external forces
The change in internal energy is equal to the heat received and the work done by external forces.
Relationship between gas work and external forces
The work of external forces is equal to the work of gas with the opposite sign.
First law through gas work
The resulting heat is spent on changing internal energy and gas work.
First law for an isothermal process
For an ideal gas at constant temperature, the heat received is equal to the work done by the gas.
Condition: The temperature of an ideal gas is constant.
First law for an isochoric process
At constant volume, the gas does no work, so heat changes the internal energy.
Condition: The volume is constant.
First law for an isobaric process
At constant pressure, heat is used to change internal energy and work.
Condition: The pressure is constant.
Heat distribution in an isobaric process
In a monatomic ideal gas, three-fifths of the heat changes the internal energy, two-fifths are converted into work.
Condition: A monatomic ideal gas expands at constant pressure.
Related formulas
The same formulas in the reference, with symbols and units.
Tasks on the topic
Statements, answer options and the walkthrough.