Chem Exam Unit 3

• Thermochemistry: Study of energy changes that accompany physical or chemical changes in matter.
• Energy: Ability to do work.
• Potential Energy: Energy stored in an object due to its position, shape or composition.
• Kinetic Energy: Energy contained in a substance based on its motion.
• Thermal energy: Et=Ep+Ek
• Heat (Q): Transfer of thermal energy from a warm substance to a cool substance.

  • Q=M*c*T
  • Measured in Joules
• Temperature (T): Measure of average kinetic energy of the particles that make up a substance.

  • Measured in Relativity, degrees Celsius or Kelvin
• Law of Conservation of Energy: Energy is neither created or destroyed; only transformed. Total energy in the universe is constant.
• System: Particles involved directly in the physical/chemical change of interest.
• Surroundings: All matter that is not part of the system.
• Euniverse= Esystem + Esurroundings

  Esystem=-Esurroundings
• Open system: Energy + matter can move in/out.

  • Firepit
  • Hot chocolate in a mug.
• Closed System: Energy can move in and out, matter cannot

  • Glowstick
  • Crockpot
• Isolated System: Neither energy or matter can move in/out

  • Thermos
  • Sealed container
• Enthalpy: Total internal energy of a substance at a constant pressure. Difficult to measure.
• Change in Enthalpy (H): Change in total enthalpy that accompanies a process. Used to study relative enthalpy or reactants and products in a system.
• Endothermic Reaction: Energy moves from surroundings to the system. Temperature of surroundings decreases.
• Exothermic Reaction: Energy moves from system into surroundings. Temperature of surroundings increases.
• Nuclear Reactions: Exothermic

  • Fusion: Small nuclei's combine to form larger, heavier nuclei
  • Fission: Large nuclei's split into smaller nuclei and collide with a neutron.
• Specific Heat Capacity (c): Amount of thermal energy needed to raise 1g of the substance by one degree Celsius/Kelvin.
• Heat Transfer: Amount of heat entering/leaving an object it is being heated/cooled.
• Calorimetry: Process of measuring thermal energy change in a chemical/physical change.
• Calorimeter: Device used to measure enthalpy change for chemical and physical changes

  • Insulates a system from its surroundings
• Molar Enthalpy Change (Hr): Energy change occurring when 1 mol of a substance undergoes a physical, chemical, or nuclear change.

  • H=nHr
• Enthalpy of Solution

  1. Bonds between solute molecules/ions are broken
  2. Bonds between solvent molecules/ions are broken
  3. Bonds must form between solute and solvent
• Potential Energy Diagrams: graphical representation of energy transferred during a physical/chemical change
• Label the diagram.

  A) Exothermic Reaction

  B) Endothermic Reation.

  C)

  
• Bond Dissociation Energy: Energy required to break a chemical bond.

  • Multiple bonds have larger bond energies than single bonds.
  • As number of bonds increases, the bond length decreases.
• Bond Energy Ideals:

  • Breaking bonds requires energy
  • Forming a new bond releases energy
  • Bond breaking is endothermic, bond making is exothermic.
• Bond energy estimates change in enthalpy

  • Total energy= Bonds broken-bonds formed
• Hess's Law of Heat Summation: Enthalpy change of a process depends only on the beginning and end conditions, (reactants and products).

  • Independent of reaction route.
• Standard State: 25 degrees Celsius, and 100 kPa
• Standard Molar Enthalpy of Formation: Amount of energy absorbed/released when one mole of a compound is formed directly from elements in their standard states.

  • Formation of element= 0
• Chemical Kinetics: Branch of chemistry dealing with rates of chemical reaction, mechanisms of reaction, factors affecting reaction rate.
• Reaction Rate: Change in amount of reactants consumed or products formed over a given interval

  Measured by increase in product concentration or decrease in reactant concentration

  Units depend on property being monitored.
• Collision Theory: Chemical reaction must involve collision of reactant particles with each other.

  1. Collisions must have sufficient energy
  2. Particles must collide with proper geometry.
• Activation Energy: The minimum amount of energy required for a reaction to occur.
• Activated Complex/Transition State: Unstable arrangement of atoms containing partially formed/unformed bonds that represent maximum potential energy point in the change.
• Factors affecting rate of reaction: Increase occurs when

  • Greater Frequency of collisions
  • Energy of particles increases
  • Activation energy is lowered.
• Nature of Reactants:

  • Rate is affected by what substances are reacting and respective state of each reactant.