Thermochemistry, Thermodynamics

• The Zeroth Law of Thermodynamics states if systems A and B are in thermal equilibrium with C, then A and B are in thermal equilibrium with each other
• Temperature is a property of matter that describes the thermal energy of a system
• Equilibrium in a system means that all forces are balanced and not opposing each other
• In thermal equilibrium, a system has an unchanging state of temperature
• Referencing the zeroth law, if system A and system B are in thermal equilibrium with system C, this means that the temperature for A and B is the same as C
• Key Terms:

  • Thermal equilibrium: the condition where two systems in contact with each other exchange no energy and have the same temperature
  • Temperature: a measure of the thermal energy in a system
• Heat itself refers to the transfer of thermal energy from a hotter object with higher temperature (energy) to a colder object with lower temperature (energy)
• Freezing point of water in Kelvin is 273 K
• Boiling point of water in Celsius is 100 °C
• The first law of thermodynamics states that the internal energy of an isolated system is constant
• Energy in the system may undergo changes but when restored to its initial state, the same energy value will be found
• The first law of thermodynamics is commonly defined as the inability to create or destroy matter
• Energy cannot be added or taken from a system, but can be transferred or converted into forms like heat or work
• The first law of thermodynamics equation: ΔU = q + w

  • ΔU represents internal energy
  • q represents heat exchange
  • w represents work exchange
• Key Points:

  • The internal energy of an isolated system is constant
  • Energy of a system can be converted into different forms such as heat or work
• Key Terms:

  • Heat: transfer of energy that results in the change of temperature
  • Work: transfer of energy that can result in the change of pressure and volume
  • Internal energy: the energy contained within the system
• Third law of thermodynamics states that the entropy of a perfectly organized crystal at absolute zero is zero.
• Formula for Fahrenheit and Celcius, and vice versa

  $F =$$9/5 C +$$32$
• Formula for Kelvin and Celcius

  $K=$$C+$$273$
• Thermal expansion is the change in volume of a material due to a change in temperature.


  Formula for thermal expansion.

  Where delta L is the change in length, alpha is the coefficient of linear expansion, L is the original length, and delta T is the change in temperature.

  
• The coefficient of linear expansion is a constant that characterizes how a specific material‘s length changes as temperature changes.
• The amount of work done by the system can be calculated by taking the integral of the function between V1 and V2
• If the final volume is greater than the initial volume, more work is done in the system
• The maximum work that can be done in a system in terms of pressure and volume is in a system with reversible gas expansion
• The area under the PV diagram describes the work done in the system.

  
• Isolated system are not capable of exchanging energy or matter with their surroundings.

  • These are rare.
  • Total internal energy must be zero.
• Closed systems are capable of exchanging energy, but not matter, with the surroundings.
• Open systems can exchange both energy and matter with the environment.

  • examples include boiling pot of water, humans, and uncontained combustion reactions are all examples of open systems.
• State functions are thermodynamic properties that are a function of only the current equilibrium state of a system. They are defined by the independent path taken to get to an equilibrium state.

  • Examples include pressure, temp, enthalpy, internal energy, Gibbs free energy, and entropy.
• Change in internal energy has a direct relationship with temperature.

  • ΔU is positive with increasing temperature.
  • ΔU is negative with decreasing temperature.
• When work is positive, work is done by the system (expansion).
• Conversion factors between the units of heat:

  $1 Cal =$$10^3 cal =$$4184 J =$$3.97 BTU$
• Conduction is the direct transfer of energy from molecule to molecule through molecular collisions.

  • Metals are the best while gases are the poorest.
• Convection is the transfer of heat by the physical motion of fluid over a material.

  • Specific to only liquids and gases.
• Radiation is the transfer of energy by electromagnetic waves.
• The Second Law of Thermodynamics states that the entropy (or disorder) of a system is constantly increasing
• Entropy is represented by Joules per Kelvin or J/K
• Entropy is the measure of the disorder of a system and can be described as the energy of a system over its temperature, represented as J/K
• Solids, liquids, and gases have different degrees of disorder, with gases being the most disordered, liquids the second most disordered, and solids the least disordered
• When a substance goes from a liquid to a solid, the entropy decreases; when a substance goes from a solid to a liquid, the entropy increases