CHEMISTRY

• Work


  The quantity of energy exchanged between a system and its surroundings
• Heat


  The kinetic energy of the molecules of the substance
• Heat and thermodynamics


  Together form the basics which helped process designers and engineers to optimize their processes and harness the energy associated with chemical reactions economically

  
• Heat energy flows from higher temperature to lower temperature

  
• Work


  Completely governed by external factors such as an external force, pressure or volume or change in temperature etc.
• Thermodynamics


  The scientific study of the interaction of heat and other types of energy

  
• Energy cannot be created nor destroyed, but it can be converted or transferred
• Internal energy


  All the energy within a given system, including the kinetic energy of molecules and the energy stored in all of the chemical bonds between molecules
• No net energy is created or lost during energy transfers and conversions
• Types of Systems


  • Open System
  • Closed System
  • Isolated System
• Open System


  Systems where the exchange of energy, as well as matter takes place
• Closed System


  Systems where only energy can be exchanged with the surrounding and not the matter
• Isolated System


  Systems where neither energy nor matter can be exchanged between the system and the surrounding
• Enthalpy


  The stored chemical energy, or heat content, of the system

  
• Exothermic Reaction


  Releases heat and light into their surroundings
• Endothermic Reaction


  Absorbs heat and/or light from their surroundings
• Catalysts lower the activation energy required for a reaction to occur, but do not affect the overall change in enthalpy of the reaction
• 1st Law of Thermodynamics

  Energy can neither be created nor destroyed, but it can be changed from one form to another
• 1st Law of Thermodynamics

  1. ΔQ = ΔU + W

  2. Where, ΔQ is the heat given or lost, ΔU is the change in internal energy, and W is the work done

  
• In a gas system with constant pressure, the loss of 50 J of heat in the surroundings and 550 J of work done on the system results in a 600 J increase in the system's internal energy
• Enthalpy


  The total content of heat of a system, equivalent to the system's internal energy plus the product of volume and pressure

  
• At constant pressure and temperature

  The flow of heat (q) equals the change in enthalpy (ΔH)

  
• Endothermic Reaction


  Absorbs heat from the surroundings, so q > 0 and ΔH > 0

  
• Exothermic Reaction


  Releases heat to the surroundings, so q < 0 and ΔH < 0

  
• Entropy (S)


  A thermodynamic quantity that measures how spread out or dispersed the energy of a system is among the different possible ways the system can contain energy
• Entropy is a state function with the SI unit of joules per Kelvin (J/K)
• Processes that lead to an increase in entropy

  • The spreading out of more concentrated molecules
  • The spreading out of more concentrated energy
• Entropy


  A measure of randomness and disorder
• Latent Heat


  The amount of heat needed to change the phase of a given mass of substance
• Spontaneous Process


  A physical or chemical change that occurs by itself without requiring an outside force, and continues until equilibrium is reached
• Spontaneous Processes


  • A lump of sugar dissolving in coffee
  • Water freezing below 0°C and melting above 0°C
  • Heat flowing from a hotter object to a colder one
  • Iron forming rust
• In a chemical reaction, the spontaneity is determined by the change in enthalpy (ΔHreaction = Hproducts - Hreactants)

  
• Water does not spontaneously reappear in its original form
• Water freezes spontaneously below 0°C, and ice melts spontaneously above 0°C (at 1 atm)
• Spontaneous process


  A physical or chemical change that occurs by itself, without requiring an outside force, and continues until equilibrium is reached
• Spontaneous processes


  • Heat flows from a hotter object to a colder one, but the reverse never happens spontaneously
  • A piece of sodium metal reacts violently with water to form sodium hydroxide and hydrogen gas, but hydrogen gas does not react with sodium hydroxide to form water and sodium
  • Iron exposed to water and oxygen forms rust, but rust does not spontaneously change back to iron
• In a chemical reaction, ΔHreaction = Hproducts - Hreactants

  
• Exothermic reaction


  ΔHreaction = (-)

  
• For a chemical reaction to be spontaneous, it should proceed as written (from left to right), without an input of energy
• Exothermicity (example 1 and 2) favors the spontaneity of a reaction but does not guarantee it. It is possible for an endothermic reaction to be spontaneous (example 3 and 4), and it is possible for an exothermic reaction to be nonspontaneous