1.1 Laws of Thermodynamics and Their Application to Combustion
3 min read•august 9, 2024
Thermodynamics is key to understanding combustion. The laws of energy conservation and guide how fuels burn and release energy. These principles are crucial for designing efficient engines and predicting reaction outcomes.
Combustion processes involve energy transfers, , and heat capacities. By applying thermodynamic concepts, we can analyze fuel efficiency, predict flame temperatures, and optimize combustion systems for better performance and reduced emissions.
Thermodynamic Laws and Properties
Fundamental Laws of Thermodynamics
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states energy cannot be created or destroyed, only converted from one form to another
Mathematically expressed as ΔU=Q−W
ΔU represents change in
Q denotes heat added to the system
W signifies work done by the system
introduces concept of entropy
Entropy of an isolated system always increases over time
Defines direction of spontaneous processes
Imposes limitations on efficiency of heat engines
Energy-Related Properties
Internal Energy encompasses total energy contained within a system
Includes kinetic energy of molecules and potential energy of molecular interactions
Depends on temperature, pressure, and composition of the system
measures heat content of a system at constant pressure
Defined as H=U+PV
U represents internal energy
P denotes pressure
V signifies volume
Entropy quantifies degree of disorder or randomness in a system
Increases during spontaneous processes
Calculated using equation ΔS=Qrev/T
Qrev represents reversible heat transfer
T denotes absolute temperature
Thermodynamic Potentials and Capacities
determines spontaneity of chemical reactions
Defined as G=H−TS
H represents enthalpy
T denotes temperature
S signifies entropy
Negative ΔG indicates spontaneous reaction
measures amount of heat required to raise temperature of a substance
refers to heat capacity per unit mass
denotes heat capacity per mole of substance
Varies with temperature and pressure
Thermodynamic Processes
Energy Transfer Mechanisms
Work involves transfer of energy through force acting over a distance
Mechanical work done by expanding gases calculated as W=−PΔV
P represents pressure
ΔV denotes change in volume
Electrical work calculated as W=qV
q signifies charge
V represents voltage
occurs infinitely slowly, allowing system to maintain equilibrium
Can be reversed by infinitesimal changes in surroundings
Ideal concept, not achievable in practice
Used as reference point for maximum efficiency
Irreversible Processes
occurs in finite time, creating entropy
Cannot be reversed without leaving a trace on surroundings
All real-world processes are irreversible
Examples include friction, heat transfer across finite temperature difference, unrestrained expansion of gas
Reaction Types
Energy Release and Absorption in Reactions
Exothermic Reaction releases heat to surroundings
Enthalpy change (ΔH) is negative
Examples include combustion reactions (burning of fuels)
Releases energy in form of heat and light
Endothermic Reaction absorbs heat from surroundings
Enthalpy change (ΔH) is positive
Examples include photosynthesis, decomposition of limestone