Thermodynamics

First law of thermodynamics

• First law of thermodynamics
• The change in the internal energy of a closed thermodynamic system is equal to the sum of the amount of heat energy (Q) supplied to or removed from the system and the work (W) done on or by the system.
• ΔU = W + Q
• Heat energy (Q) supplied to the system and the work (W) done on the system are positive.
• Heat energy (Q) removed from the system and the work (W) done by the system are negative.

Second law of thermodynamics

• Not all processes, that theoretically might occur according to the first thermodynamic law, will ever occur in nature. .e. g. .:
• When we touch together a hot and a cold object, we observe that energy is passed away from the wormer to the cooler object. We never observe opposite situation.
• Substance dissolved in solvent diffuses from the areas with higher concentration to the areas with lower concentration. The direction of difusion is never from lower to higher concentration.

All thermodynamic processes can occur spontaneousely in specified direction only – from more ordered states to less ordered states.

• All thermodynamic processes can occur spontaneousely in specified direction only – from more ordered states to less ordered states.
• The processes are irreversible.

• A

• B

• A

• B

• S2

• S1

• S2 > S1

It is not possible for the system to become spontaneousely ordered again. Gas particles will not gather again in containar A, while containar B will not become spontaneousely empty.

• It is not possible for the system to become spontaneousely ordered again. Gas particles will not gather again in containar A, while containar B will not become spontaneousely empty.
• It is possible to empty containar B, but this process will not be spontaneous. If we perform the process, then the entropy of the system will be decresed.