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It is necessary for the students to understand the basic concept behind the first law of thermodynamics chemistry and then read it. The study of relationships among work, heat and temperature and their relationship with energy, entropy, and the physical properties of matter. Thermodynamics describe how matter is affected by the process when the thermal energy changes to or from the other forms of energy and also the process itself.
The energy which is released from heat is termed as thermal energy. This generated heat permits the movement of particles within an object and as the speed of these particles increases, the generation of heat also increases.
In this article we will learn about the first law of thermodynamics chemistry.
Introduction
According to the first law of thermodynamics the energy of the universe always remains the same. Energy may be exchanged between the system and the surroundings but it can’t be created or destroyed. This first law of thermodynamics basically related to the changes in the state of energy due to work and heat transfer. It basically redefines the conservation of energy.
Definition
According to the first law of thermodynamics the quantity of the heat absorbed when some amount of heat is given to a system which is capable of doing external work is always equal to the sum of the increase in internal energy of the system because of rise in temperature and the external work done during expansion.
The first law of thermodynamics chemistry is represented by the equation
U=Q-W
Here,
U = Change in internal energy
Q = Heat provided to the system
W = Work done
The differential form of the first law of thermodynamics is
dU=dQ-dW
As we study, the first law of Thermodynamics is similar to the Law of conservation of energy, hence it is also known as Law of Conservation of Energy.
Law of Conservation of Energy
According to the law of conservation of energy “Energy can neither be created nor be destroyed, it can be only transferred from one form to another form”.
Important points
- The energy (E) always remains constant for an isolated system.
- Internal Energy is a point function and property of the system. Internal energy is an extensive property (means mass-dependent) whereas specific energy is an intensive property (means independent of mass).
- The internal energy is a function of temperature for an ideal gas.
When a thermodynamic system is in an equilibrium state then it possesses a state variable which is termed as the internal energy(E). The change in the internal energy is the difference of the heat transfer into the system and the work done by the system.
State Variable
Thermodynamic state variables are defined as the macroscopic quantities that determine the equilibrium state of a system. A system which is not in equilibrium state cannot be determined by state variables.
There are two types of state variable
Intensive Variables
The intensive variable is the variable which is independent from the dimensions of the system such as temperature and pressure.
Extensive Variable
The extensive variable is the variable which is dependent on the size of the system for e.g mass, volume.
Sign Conventions
The table which is given below will show the sign conventions for the three quantities.
ΔU (change in internal energy) | Q (heat) | W (work done on the gas) |
“+” when the temperature increases. | “+” when the heat enters gas | “-” when the gas is compressed |
“-” when the temperature degrades. | “-” when the heat exist gas | “+” when the gas expands |
“0” when the temperature is constant | “0” when there is no exchange of heat | “0” when the volume is constant |
Application of First Law of Thermodynamics
- First law of thermodynamics can be seen in the process of sweating.
- The first law of thermodynamics can be seen when a piece of ice soaks the drink, it is put into.
- Sweating is an example of the first law of thermodynamics because heat of the body is transferred to sweat.
Limitations of First Law of Thermodynamics
There are some limitations of the first law of thermodynamics. First law of Thermodynamics limitations are
- The first law of thermodynamics does not describe the direction of flow heat.
- The process is not reversible and it is hard to differentiate whether the process is spontaneous or not.
Conclusion
Thermodynamics will be understood with the help of some laws. The simplest law among these laws is the first law. According to the first law of thermodynamics the energy of the universe always remains the same. Energy may be exchanged between the system and the surroundings but it can’t be created or destroyed. This first law of thermodynamics basically related to the changes in the state of energy due to work and heat transfer. It basically redefines the conservation of energy. In this article we learn about the definition of the first law of thermodynamics, the formulation of the first law of thermodynamics, it’s applications and also its limitations.
