AP Physics 2: Algebra-Based Flashcards: The First Law of Thermodynamics
Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026
Review key ideas with interactive flashcards. This set includes 14 cards to help you master important concepts.
What fundamental principle is the first law of thermodynamics a restatement of?
The first law of thermodynamics is a restatement of the conservation of energy, accounting for energy transferred into or out of a system by work and heat.
Card 1 of 14
All Flashcards (14)
What fundamental principle is the first law of thermodynamics a restatement of?
The first law of thermodynamics is a restatement of the conservation of energy, accounting for energy transferred into or out of a system by work and heat.
A system's internal energy decreases by 150 J while 100 J of heat is removed from it. Was work done on the system or by the system, and how much?
Work was done on the system. Using ΔU = Q + W, we get -150 J = -100 J + W, so W = -50 J. A negative W means work was done by the system.
In the equation W = -PΔV, what does a positive value for W signify?
A positive value for W signifies that work was done on the system by its surroundings, which occurs when the system's volume decreases (compression).
A gas expands, pushing a piston. Is the work (W) done on the gas system positive, negative, or zero?
The work done on the system is negative because the system's volume increased (ΔV is positive), meaning the system did work on its surroundings.
What general term is used to describe the changes in a system's state, and how are these changes often visualized?
These changes are called thermodynamic processes and are often visualized using pressure-volume (PV) diagrams.
If the temperature of an ideal monatomic gas is doubled, how does its internal energy change?
Its internal energy also doubles, as the internal energy of an ideal monatomic gas is directly proportional to its absolute temperature.
How is the work done on a system calculated when its volume changes against a constant external pressure?
The work done on the system is calculated using the equation W = -PΔV.
What is the internal energy of a system?
The internal energy of a system is the sum of the kinetic energy of its constituent objects and the potential energy of the configuration of those objects.
A system absorbs 200 J of heat and has 50 J of work done on it. What is the change in the system's internal energy?
The change in internal energy is +250 J. Using ΔU = Q + W, we get ΔU = (+200 J) + (+50 J) = 250 J.
What is the mathematical equation for the first law of thermodynamics?
The equation is ΔU = Q + W, where ΔU is the change in internal energy, Q is the heat added to the system, and W is the work done on the system.
How is the internal energy of an ideal monatomic gas defined?
The internal energy of an ideal monatomic gas is simply the sum of the kinetic energies of its atoms, as intermolecular potential energies are considered negligible.
What is a pressure-volume (PV) diagram?
A PV diagram is a graph used to represent the state changes of a system, known as thermodynamic processes, by plotting pressure versus volume.
According to the first law of thermodynamics, what are the two ways to change a system's internal energy?
The internal energy of a system can be changed by transferring energy through heating/cooling (Q) or by doing work on or by the system (W).
State the equation for the internal energy (U) of an ideal monatomic gas in terms of temperature.
The internal energy is given by the equation U = (3/2)nRT or U = (3/2)Nk_B T.