Unit-2: Zeroth and First Law of Thermodynamics
Unit-2: Zeroth and First Law of Thermodynamics
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Heat
Heat
- Energy can cross the boundary of a system in two distinct forms: heat and work.
- Heat is a form of energy which transfers between a system and its surroundings due to a temperature difference.
- Heat is energy in transit, not energy stored in a body.
- Heat always flows naturally from a higher-temperature body to a lower-temperature body.
- Heat transfer stops when thermal equilibrium is reached.
- Heat transfer can occur by: Conduction, Convection and Radiation
- The SI unit of heat is Joule (J).
- Heat is represented by Q.
Work
Work
- Work is said to be done by a system if the sole effect of the things external to the system is equivalent to the lifting of a weight, even if the weight is not actually lifted.
- Work transfer occurs when something crosses the boundary of a system, Hence, work is a boundary phenomenon.
- Work is represented by W.
- The SI unit of work is Joule (J).
- Work is a path function, meaning its value depends on the path followed during a process.
- Work can be transferred to or from a system.
Sign convention
Sign convention
- Heat and work are directional quantities, and thus the complete description of a heat or work interaction requires the specification of both the magnitude and direction.
- Heat added to a system and work done by a system are positive.
- Heat removed from a system and work done on a system are negative.
Equation of Non-Flow or Close System Work
Equation of Non-Flow or Close System Work
- Work = Force x displacement
- dW = p x dA x dx
- dW = p x dV
- Conditions:
- Area under the curve on PV diagram project on volume axis represents work.
Zeroth law of thermodynamics
Zeroth law of thermodynamics
- If two systems are each in thermal equilibrium with a third system, then they are in thermal equilibrium with each other.
- Two systems are in thermal equilibrium when there is no net heat transfer between them.
- It provides the basis for the concept of temperature.
- It establishes temperature as a measurable property.
- It is the fundamental principle behind the operation of thermometers.
Temperature
Temperature
- The temperature is a thermal state of a body which distinguishes a hot body from a cold body.
- The temperature of a body is proportional to the stored molecular energy i.e., the average molecular kinetic energy of the molecules in a system.
- Instruments for measuring ordinary temperatures are known as thermometers and those for measuring high temperatures are known as pyrometers.
Temperature Scale
Temperature Scale
- The Zeroth Law of Thermodynamics provides the basis for measuring temperature.
- Temperature scale is based on the zeroth law because it allows temperature to be measured by comparing thermal equilibrium states.
- Temperature scales use fixed reference points.
- Ice point: freezing point of water at 1 atm = 0°C = 32°F
- Steam point: boiling point of water at 1 atm = 100°C = 212°F
- Celsius (°C): common SI scale
- Fahrenheit (°F): English unit scale
- Kelvin (K): absolute SI temperature scale
- Thermodynamic scale is independent of substance properties
- Ideal-gas temperature scale is nearly the same as Kelvin
- Triple point of water = 273.16 K
- Absolute zero = 0 K = −273.15°C
First law of thermodynamics
First law of thermodynamics
- Energy can neither be created nor destroyed; it can only be transformed from one form to another.
- Heat supplied to a system is used to increase its internal energy and/or to do work.
Application of First Law to closed systems
Application of First Law to closed systems
- coming soon.....
Application of First Law to open systems
Application of First Law to open systems
- coming soon.....
Steady Flow Energy Equation – SFEE
Steady Flow Energy Equation – SFEE
- coming soon.....
Perpetual motion machine of the first kind (PMM-1)
Perpetual motion machine of the first kind (PMM-1)
- A Perpetual Motion Machine of the First Kind (PMM-1) is a hypothetical machine that produces continuous work without receiving any energy input.
- It violates the First Law of Thermodynamics, because it creates energy without any corresponding energy input.
Questions
Questions
1. Explain the macroscopic and microscopic approaches to thermodynamic analysis.
2. Define a thermodynamic system, surroundings, boundary, and control volume.
3. Explain the different types of thermodynamic systems with suitable examples.
4. Define state, path, process, and cycle. Explain each with suitable examples.
5. Explain the state postulate. What is its significance in determining the state of a thermodynamic system?
6. Differentiate between point function and path function. Also explain quasi-static process and thermodynamic equilibrium.
2. Define a thermodynamic system, surroundings, boundary, and control volume.
3. Explain the different types of thermodynamic systems with suitable examples.
4. Define state, path, process, and cycle. Explain each with suitable examples.
5. Explain the state postulate. What is its significance in determining the state of a thermodynamic system?
6. Differentiate between point function and path function. Also explain quasi-static process and thermodynamic equilibrium.
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