laws of thermodynamics

• Loss of thermodynamics


  Helps us understand why energy flows in a certain direction and in a certain ways
• Laws of thermodynamics


  • Zeroth law
  • First law
  • Second law
  • Third law
• First law of thermodynamics


  Law of conservation of energy - energy is not created nor destroyed, it only changes forms
• Second law of thermodynamics


  The entropy of the universe is always increasing
• Third law of thermodynamics


  The entropy of perfect crystals at absolute zero is zero
• Zeroth law of thermodynamics


  If two bodies are each in thermal equilibrium with some third body, then they are also in equilibrium with each other
• The zeroth law of thermodynamics is the fundamental basis for the first three laws
• Zeroth law of thermodynamics

  If two systems are in thermodynamic equilibrium with a third system, the two original systems are in thermal equilibrium with each other
• Example of first law of thermodynamics

  • Wind turbine converts kinetic energy in the wind into mechanical energy and then into electrical energy
• Entropy


  The degree of disorder within a system
• Entropy of the universe

  Always increasing
• A perfectly crystalline solid at absolute zero has an entropy of zero
• Absolute zero is the coldest temperature possible, at 0 Kelvin or -273.15 degrees Celsius
• Absolute zero may not be achievable experimentally due to the second law of thermodynamics
• enthalpy


  the measure of total heat in a system under constant pressure
• Ralph H. Fowler


  British physicist who first formulated and labeled the zeroth law of thermodynamics
• Spontaneity


  generally associated with natural occurrences or those that proceed even without an external triggering force
• iron sheets spontaneously undergo corrosion in the presence of air and moisture form iron oxide
• cool objects cannot react spontaneously without heat
• spontaneous reaction - associated with an increased entropy of a system and its surroundings
• ordered system - low entropy
• disordered system - high entropy
• entropy increases if the reaction yields gases, and decreases if the reaction involves the conversion of a gas to solid or liquid
• the increase should refer to the net entropy, the sum should be positive
• entropy changes based on a change in volume and heat. temperature and physical phase
• positive ∆S
 has spontaneous reaction in a certain direction
• negative ∆S
 has spontaneous reaction in opposite direction
• zero ∆S
 reaches equilibrium
• the extent of change in entropy depends inversely on the temperature and directly on the direction on the heat flow
• • Exothermic reaction releases energy at high temperature = random motion of atoms in the surroundings = minimum entropy
  • Exothermic reaction releases energy at low temperature=slower motion of atoms in the surroundings = maximum entropy
  • Endothermic reaction absorbs heat from the surroundings, therefore, tends to decrease the entropy of the surroundings
• • At a constant temperature and pressure, a reaction is spontaneous in a certain direction if ∆G is negative
  • If ∆G is positive, the opposite direction would be spontaneous.
  • A system is equilibrium if ∆G =0
• standard free energy - the change in free energy when the reactants in their standard phase yield products of the same phase