10.1 First Law of Thermodynamics in Chemical Processes

The First Law of Thermodynamics is the foundation for understanding energy changes in chemical processes. It states that energy can't be created or destroyed, only converted between forms, and provides a mathematical framework for calculating energy changes.

Energy in chemistry takes various forms, including kinetic, potential, internal, thermal, chemical, and electrical. These forms can interconvert during reactions and processes, making it crucial to track energy flows and transformations in chemical systems.

Fundamentals of the First Law of Thermodynamics

Energy changes in chemical processes

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• First law of thermodynamics states energy cannot be created or destroyed, only converted between forms
• Mathematical expression $\Delta U = Q - W$ calculates change in internal energy from heat added and work done
• Sign conventions define positive Q as heat added to system and positive W as work done by system
• Application to chemical processes ensures energy conservation in reactions, accounts for heat effects, and considers work from volume changes (expansion/compression)

Forms of energy in chemistry

• Kinetic energy represents motion, depends on mass and velocity (moving molecules)
• Potential energy stems from position or configuration, includes gravitational (elevated reactants) and chemical (bond energies)
• Internal energy sums all microscopic energies, encompasses molecular kinetic and potential energies
• Thermal energy relates to temperature, involves heat capacity and specific heat (heating/cooling reactions)
• Chemical energy stored in bonds, released or absorbed during reactions (exothermic/endothermic)
• Electrical energy from charges, crucial in electrochemical processes (batteries, electrolysis)
• Interconversions occur between energy forms:
  • Chemical to thermal in exothermic reactions (combustion)
  • Thermal to kinetic in heat engines (steam turbines)
  • Potential to kinetic when objects fall (hydroelectric power)
  • Chemical to electrical in batteries (lithium-ion)

Energy Balances and Thermodynamic Functions

Energy balance in chemical systems

• Closed systems prevent mass transfer, use energy balance $\Delta U = Q - W$
• Open systems allow mass and energy flow, apply $\Delta H = Q - W_{shaft}$
• Solving energy balance problems involves:
  1. Defining system boundaries
  2. Identifying inputs/outputs
  3. Applying appropriate equation
  4. Accounting for all energy terms
  5. Solving for unknowns
• Steady-state processes maintain constant system properties, while unsteady-state see changes over time (batch vs continuous reactors)

State vs path functions

• State functions depend only on current system state, independent of path (U, H, S)
• Path functions rely on the process route between initial and final states (Q, W)
• Calculations with state functions use initial and final states directly
• Path functions require knowledge of specific process steps
• Exact differentials (dU) represent state function changes, independent of path
• Inexact differentials (đQ, đW) denote path function changes, path-dependent
• First law relates exact (dU) and inexact (đQ, đW) differentials