state and explain first law of thermodynamics
Answers
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→ The heat energy absorbed by a system is equal to the sum of the increase in the internal energy and the external work done by the system on the surroundings.
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→ Let dQ be the amount of heat absorbed by the system, dU be the increase in internal energy and dW be the external work done, then 1st law of thermodynamics.
- dQ = dU + W
→ This is according to the law of conservation of energy significance of 1st law of thermodynamics: Law of conservation of energy.
→ Isothermal process:- It is the process which takes place at constant temperature.
→ Isothermal change is represented by the equation, PV = constant.
→ Where P is the pressure and V is the volume.
→ Example:- Melting of ice and boiling of water.
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Conditions to obtain isothermal process are as follows:-
→ There must be conducting path between the system and surroundings.
→ The changes should take place very slowly.
According to the first law of thermodynamics, during any transformation, there is conservation of energy.
In the case of closed thermodynamic systems, it is stated as follows:
"During any transformation of a closed system, the variation of its energy is equal to the quantity of energy exchanged with the external environment, by thermal transfer (heat) and mechanical transfer (labor). "
ΔQ = ΔU + W
where,
Q = Heat supplied to system
U = Increase in internal energy
W = Work done by system
The variation of the energy of a system which undergoes a transformation can be expressed according to the following relation:
ΔE = ΔU + ΔEc + ΔEp = W + Q
ΔE = the sum of the different energy variations of the system.
ΔU = increase in internal energy
ΔEc = the variation of the macroscopic kinetic energy of the system
ΔEp = the variation of the potential energy of the system
ΔW = Work done by system
ΔQ = Heat supplied to a system