First Law of Thermodynamics provides important insight into the behavior of energy in the universe. Often known as the law of energy conservation, it basically asserts that energy can only be changed from one form to another; it cannot neither be created nor be destroyed. This law plays a vital role in the of how energy moves through chemical reactions and processes.
Energy and Its Forms
Thermal energy: The random motion of molecules, often referred to as heat.
Chemical energy: Stored in the bonds between atoms and molecules.
Electrical energy: Associated with the movement of electrons or charged particles.
First Law of Thermodynamics:-
First Law of Thermodynamics in its simplest form can be expressed as: ΔU = q + w
Here, ΔU represents the change in the internal energy of a system, q is the heat exchanged between the system and surroundings, and w is the work done by the system.
Internal Energy (U): This describes the total energy present in a system, which includes the potential energy held in chemical bonds as well as the kinetic energy of individual particles. Since it’s a state function, its value is determined only by the system’s current state and not by the process by which it got there.
Heat (q): Energy that is transferred when a system’s temperature differs from that of its surroundings is known as heat. Q is positive if the system takes in heat from its surroundings; it is negative if it releases heat.
Work (w): Energy transferred when a force moves anything is referred as work. This is frequently connected to the expansion or compression of gases in chemistry. A gas work on its surroundings when it expands against external pressure, and w is negative. w is positive if the environment have any influence on the system (for example, by compressing a gas).
Energy Conservation in Chemical Reactions
Chemical reaction that is taking place inside a closed container. We refer to a reaction as exothermic if it releases energy and transfers heat to the environment (q is negative). Heat enters the system when a reaction consumes energy and is endothermic (q is positive).
An isolated system’s total energy stays constant, which is a important effect of the First Law of Thermodynamics. Therefore, the total energy content of the system and its surroundings remains unchanged even though energy may change forms throughout a reaction (chemical energy converting into thermal energy).
Relationship Between Heat and Work
Work and heat are two factors in many chemical processes. Burning of a fuel in oxygen (O2), such as methane (CH4). In addition to producing a large amount of heat, the reaction yields carbon dioxide (CO2) and water (H2O). A portion of the energy released is utilised to cause the gases to expand, changing the surrounding environment; the remaining energy is released as heat, warming the environment.
Reaction between the methane and oxygen is an example of the First Law in action, where the total energy change in the system is equal to the sum of the work done on the environment and the heat released. The overall energy stays the same regardless of whether it manifests as heat or work.
Applications in Chemistry
First Law of Thermodynamics has innumerable applications in chemistry. It’s essential to understand how enthalpy varies during chemical processes. For many processes, the enthalpy change (ΔH) is equal to the heat transferred. Enthalpy (H) is a measure of a system’s total heat content at constant pressure.
Furthermore, the First Law explains why certain reactions require energy input while others occur spontaneously. While the system’s overall energy is preserved, activities such as the melting of ice require the absorption of heat from the environment in order to change states.
To know the main points:-
(i) Energy can neither be created nor be destroyed.
(ii) The total energy of universe is constant.
(iii) The mass and energy of an isolated system remains constant.
(iv) The total energy of a system and its surrounding must remain constant, although it may be changed from one form to other.
Mathematical expression:- ΔU = q + W
Whereas, W = +ve, work done on the system
W = -ve, work done by the system
q = +ve, heat is observed by the system
q = -ve, heat is evolved by the system
Example:- A system gives out 13 J of heat and also 26 J of work. What is the internal energy change?
Solution :- ΔU = q + w
= -13 J + (-26) J
= -39 J
Note:-
The basic idea guiding energy interactions in chemistry is known as the First Law of Thermodynamics. It gives us comfort in knowing that although energy can be moved and changed, the universe’s overall energy remains constant. We can more accurately forecast reaction outcomes, create effective procedures, and investigate the nature of chemical energy by how energy travels as heat and work in chemical reactions.
First Law of Thermodynamics, normally referred as the Law of Energy Conservation, energy cannot be generated or destroyed in a system that is isolated. In chemistry, it indicates that although energy can move between a system and its surroundings as heat or work, the overall energy of the system and its surroundings stays constant during a chemical process.
The following formula represents the First Law of Thermodynamics:
ΔU = q + w
where w is the work completed, q is the heat exchanged, and ΔU is the change in internal energy of the system. This formula illustrates how internal energy varies with heat and work interactions with the environment.
The overall energy present in a system, including the potential energy held in chemical bonds as well as the kinetic energy of particles, is known as internal energy (U). It is a state function, its value is solely depend on the system’s current state.
Work (w) is the energy transferred when a force moves something, like when a gas expands or contracts, whereas heat (q) is the energy transferred between the system and surroundings as a result of a temperature difference. A system’s internal energy can be altered by work or heat.
No, the First Law of Thermodynamics states that energy cannot be destroyed. It can only transform into other forms, like mechanical work or heat energy from chemical energy. In every process, the whole amount of energy is conserved.
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