Zeroth and First Laws of Thermodynamics
The zeroth law defines temperature through thermal equilibrium; the first law states DU = Q - W, energy conservation including heat.
What is Zeroth and First Laws of Thermodynamics?
The zeroth law defines temperature through thermal equilibrium; the first law states DU = Q - W, energy conservation including heat.
Key formula / rule: DU = Q - W with W the work done by the gas.
Key points
- Apply the first law to standard processes.
- Distinguish state functions from path functions.
Common exam trap
Treating heat as a quantity stored in a body.
Definitions
- Term
Zeroth and First Laws of Thermodynamics
- Meaning
The zeroth law defines temperature through thermal equilibrium; the first law states DU = Q - W, energy conservation including heat.
- Term
Zeroth and First Laws of Thermodynamics — explanation
- Meaning
Internal energy is a state function while heat and work are path dependent, which is why sign conventions must be stated once and kept. For an ideal gas U depends only on temperature.
Learning objectives
Apply the first law to standard processes.
Distinguish state functions from path functions.
Formulae
- Key point
DU = Q - W with W the work done by the gas.
- Key point
U is a state function; Q and W are path functions.
- Key point
For an ideal gas, U depends only on temperature.
Prerequisites
PHY-U3-THR-T1-S1-C2
PHY-U1-WEP-T1-S1-C1
Common mistakes
Treating heat as a quantity stored in a body.
Mixing sign conventions for work done on and by the gas.
Keywords
Zeroth
First
Thermodynamics
Practice preview
The Zeroth Law of Thermodynamics helps to define which of the following physical quantities?…
easy
In the First Law of Thermodynamics (DU = Q - W), if work is done ON the system, what is the sign convention for W?…
easy
For an ideal gas undergoing an isothermal process, what is the change in internal energy (DU)?…
medium