First Law of Thermodynamics: Energy cannot be created or destroyed; it is transferred between systems.
Energy transfer occurs via heat and work.
Internal Energy (U): The energy contained within a system.
Energy Transfer
Heat (Q): When heat flows into a system, the system gains internal energy.
Work (W): Work done on a system by surroundings increases the system's internal energy.
Example: If surroundings do 300 joules of work on a system, the system's internal energy increases by 300 joules.
Analogy
Money Transaction: Similar to energy, money is transferred from one account to another without being created or destroyed.
Types of Systems
Open System:
Both matter and energy can be transferred into and out of the system.
Closed System:
Only energy can be transferred; matter cannot enter or leave the system.
Isolated System:
Neither matter nor energy can enter or leave; total energy and mass remain constant.
Equations
Chemistry Equation:
( \Delta U = Q + W )
Chemistry takes the system's perspective.
Physics Equation:
( \Delta U = Q - W )
Physics takes the surroundings' perspective.
Sign Conventions
Chemistry:
Work done by the system: ( W < 0 )
Work done on the system: ( W > 0 )
Physics:
Work done by the system: ( W > 0 )
Work done on the system: ( W < 0 )
Heat Processes
Endothermic Process:
Heat absorbed by the system: ( Q > 0 )
Exothermic Process:
Heat released by the system: ( Q < 0 )
Perspective in Analysis
System's Perspective: Focus on how energy changes within the system.
Surroundings' Perspective: Focus on energy changes in the surroundings.
Conclusion
Understanding the first law of thermodynamics involves recognizing how energy is transferred and represented through different perspectives in chemistry and physics.
Future lessons will include practice problems to apply these concepts.