Definitions:        

System:  Any specific part of universe that is of interest to us.

Surroundings:  The universe outside the system is surroundings.

Open system:  System that can exchange mass and energy with its surroundings.

Closed system:  System that can exchange energy but not mass with its surroundings.

Isolated system:  No transfer of either mass or energy.

Exothermic process:  Any process that gives of heat.

Endothermic process:  Process in which heat has to be supplied to the system by the surroundings.

Internal energy:  Energy of a substance due to its molecular structure and motion.

External energy:  Energy of a substance due to its position or motion.

Enthalpy:  Heat released or absorbed in a constant pressure process is called enthalpy.

Specific heat:  Amount of heat required to raise the temperature of one gram of substance by one degree Celsius.

Heat of solution:  Heat generated or absorbed when a certain amount of solute dissolves in a certain amount of solvent.

Spontaneous reactions:  A reaction that does occurs under given set of conditions (e.g. at given temperature, pressure and concentration).

 

Laws in one sentence:

1^st law of thermodynamics: Energy can be converted from one form to another, but cannot be created or destroyed.

2^nd law of thermodynamics:  The entropy of the universe increases in a spontaneous process and remains unchanged in an equilibrium process.

3^rd law of thermodynamics:  The entropy of a perfect crystalline substance is zero at the absolute zero temperature.

Hess’s law:  When reactants are converted to products, the change in enthalpy is same whether the reaction takes place in one step or in a series of steps.

Law of conservation of energy:  The total energy in the universe is constant.

 

Important Formulas:

1. First Law of Thermodynamics (Conservation of Energy): ΔU=Q−WΔU=Q−W This equation states that the change in the internal energy (ΔUΔU) of a system is equal to the heat added to the system (QQ), minus the work done by the system on its surroundings (WW). It represents the principle of energy conservation, indicating that energy cannot be created or destroyed, only transformed.
2. Second Law of Thermodynamics (Entropy): ΔS≥QTΔS≥TQ​ This formula expresses that the change in entropy (ΔSΔS) of a system is greater than or equal to the heat transfer (QQ) divided by the temperature (TT) in Kelvin. The second law highlights the direction of spontaneous processes, indicating that total entropy in an isolated system can never decrease over time.
3. Work Done by a Gas (at constant pressure): W=PΔVW=PΔV This equation calculates the work done by a gas when it expands or contracts at constant pressure (PP), where ΔVΔV is the change in volume. This formula is particularly useful in describing processes such as isobaric expansions or compressions.
4. Efficiency of a Heat Engine: η=WoutQin=Qin−QoutQinη=Qin​Wout​​=Qin​Qin​−Qout​​ Efficiency (ηη) of a heat engine is the ratio of work output (WoutWout​) to the heat input (QinQin​). This formula is key in understanding how much useful work is produced by a heat engine compared to the heat energy it consumes.
5. Carnot Efficiency: ηCarnot=1−TCTHηCarnot​=1−TH​TC​​ The Carnot efficiency is the theoretical maximum efficiency of a heat engine operating between two reservoirs at temperatures THTH​ (hot reservoir) and TCTC​ (cold reservoir). It sets an upper limit on the efficiency of all real engines.
6. Specific Heat Capacity: Q=mcΔTQ=mcΔT This formula calculates the heat (QQ) absorbed or released by a substance, where mm is the mass, cc is the specific heat capacity, and ΔTΔT is the change in temperature. Specific heat capacity is a measure of the amount of heat per unit mass required to raise the temperature by one degree Celsius (or Kelvin).
7. Gibbs Free Energy: ΔG=ΔH−TΔSΔG=ΔH−TΔS Gibbs Free Energy (ΔGΔG) change is used to predict the spontaneity of a process at constant pressure and temperature. It incorporates enthalpy change (ΔHΔH), temperature (TT), and entropy change (ΔSΔS). A negative ΔGΔG indicates a spontaneous process.
8. Enthalpy (Heat) Change: ΔH=QpΔH=Qp​ This equation defines the change in enthalpy (ΔHΔH) of a system undergoing a process at constant pressure, where QpQp​ is the heat exchanged with the surroundings. Enthalpy change is a key concept in chemical thermodynamics for reactions and phase changes.