Chemistry

• 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 rock at the top of a hill rolls down
  • Heat flows from a hot object to a cold one
  • An iron object rusts in moist air
• Entropy (S)


  A thermodynamic quantity that is a measure of how spread out or dispersed the energy of a system is among the different possible ways that system can contain energy
• The SI unit of entropy is joules per Kelvin (J/K)
• Entropy is a state function
• Second Law of Thermodynamics

  • The total entropy of a closed system cannot decrease
  • Within a system, entropy of one system can decrease by raising entropy of another system
• Some scientists predict the entropy of the universe will increase to the point where the randomness creates a system incapable of useful work, leading to the "heat death" of the universe
• Other scientists dispute the theory of heat death, considering the universe as part of a larger system or saying the possible states do not have equal likelihood
• Entropy increase


  • A block of ice melting
  • Water changing to steam
• Entropy


  Often called the "arrow of time" because matter in isolated systems tends to move from order to disorder
• Chemical kinetics


  The study of chemical processes and rates of reactions, including the analysis of conditions that affect speed of a chemical reaction, understanding reaction mechanisms and transition states, and forming mathematical models to predict and describe a chemical reaction
• Peter Waage and Cato Guldberg formulated the law of mass action


  1864
• Jacobus van't Hoff published "Etudes de dynamique chimique"


  1884
• Jacobus van't Hoff awarded the Nobel Prize in Chemistry


  1901
• Factors that affect chemical reaction rate


  • Concentration of reactants
  • Temperature
  • Presence of catalysts
  • Physical state of reactants
  • Pressure
• Collision theory


  Molecules must collide in order to react, and they must have sufficient energy to disrupt bonds
• Activation energy


  The energy that must be overcome in order for a reaction to occur, the minimum energy required to start a chemical reaction
• As temperature rises


  Molecules move faster and collide more vigorously, increasing the likelihood of bond cleavages and rearrangements
• Reaction speed


  • Rusting of iron (slow)
  • Digestion of food (medium)
  • Esterification of acetic acid (medium)
  • Formation of silver chloride precipitate (fast)
• Thermochemistry


  Deals with heat (energy) changes in chemical reactions
• Endothermic reactions


  • Reaction absorbs heat
• Endothermic reactions


  • Vaporization of water
  • Sublimation of naphthalene
  • Solvation of sugar in water
• Endothermic reactions


  Potential energy of reactants is lower than potential energy of products, so heat is given to the reaction
• Exothermic reactions


  Reaction releases heat
• Exothermic reactions


  • Condensation of gases
  • Combustion reactions
• Exothermic reactions


  Potential energy of reactants is higher than potential energy of products, so excess energy is released
• Enthalpy


  Total kinetic and potential energy of particles of matter
• Mole fraction


  A way of describing solution composition. It is the ratio of the number of moles of one component of a mixture to the total number of moles of all components.
• Enthalpy change


  Heat gained or lost in reactions under constant pressure
• Molality


  The ratio of the number of moles of solute to the mass of the solvent in kilograms.
• In exothermic reactions


  Enthalpy of reactants is larger than enthalpy of products, so enthalpy change is negative
• In endothermic reactions


  Enthalpy of products is larger than enthalpy of reactants, so enthalpy change is positive
• Molality does not change with the solution's temperature, unlike molarity which can change due to volume changes.
• Enthalpy change depends on temperature and pressure, so reactions should be compared under the same conditions
• Molarity measures the number of moles of solute per liter of solution, while molality measures the number of moles of solute per kilogram of solvent.
• Standard reference state


  Enthalpy change measured under 1 atm pressure and 25°C temperature
• Thermochemical reactions


  Reactions showing both changes of matter and energy
• Hess' law


  1. Sum one or more reactions to form a new reaction

  2. Apply the same changes to the enthalpy changes of the used reactions
• Chemical kinetics


  The study of chemical processes and rates of reactions, including the analysis of conditions that affect speed of a chemical reaction, understanding reaction mechanisms and transition states, and forming mathematical models to predict and describe a chemical reaction
• Peter Waage and Cato Guldberg formulated the law of mass action


  1864