Chemistry Pre-finals

• Rate of chemical reaction


  The speed by which reactants are converted to products
• Measuring rate of chemical reaction

  1. Change in the concentration of the reactants and products

  2. As the reactants disappear, products appear

  
• Requirements for a chemical reaction to occur

  • Sufficient Energy- Activation energy is the energy needed to start a reaction
  • Proper orientation of the colliding particles (Collision Theory)- Reactant particles require sufficient kinetic energy to initiate successful collisions that will lead to the formation of products
• Five factors that affect the rate of reaction

  • Temperature
  • Concentration of the reactants
  • Particle size
  • Presence or absence of a catalyst
  • Nature of the reactants

  
• Heat (Q)


  Energy transferred from one object to another due to their temperature difference
• Work (W)


  The energy transferred when an object is moved against force
• Thermodynamics


  The study of the energy changes that accompany all processes, whether chemical or physical
• Thermochemistry


  The study of heat and energy changes that accompany chemical transformation in matter
• Changes can either

  • Release energy
  • Absorb energy
• Calorimetry


  Measuring energy changes in chemical reactions. It measures the energy

  
• Heat of reaction


  The total amount of heat obtained, which is actually the energy change when the reaction occurs
• Enthalpy Change, H


  The heat transferred by a process that occurs at constant pressure
• Heats of Reactions are good approximations of the enthalpy changes and are often referred to interchangeably
• Universe


  The observable, physical world
• System


  The limited, defined part of the universe
• Surroundings


  All parts of the universe not included in the defined system
• Internal Energy (U)


  Energy contained within the system
• Internal Energy (U) can be changed by

  • Heating the system
  • Doing work on it
  • Adding or taking away matter
• Q > 0 (+)


  Heat is absorbed by the system (endothermic)
• Q < 0 (-)


  Heat is released by the system (exothermic)
• W > 0 (+)


  Work done on the system
• W < 0 (-)


  Work done by the system
• Chemical Thermodynamics


  The chemistry that deals with the energy and entropy changes and the spontaneity of a chemical process
• Spontaneous Processes


  Processes taking place on their own without any external aid
• In general, spontaneous reactions are exothermic
• Nonspontaneous Processes


  Changes that do not happen on their own
• Entropy, S


  One property common to spontaneous processes is that the final state is more disordered or random than the original
• Spontaneity is related to an increase in randomness
• Factors that increase entropy

  • Temperature increases
  • Physical states change from solid to liquid to gas
  • Dissolution of a solid or liquid in a solvent
  • Dissolution of a gas
• Factors that decrease entropy

  • Physical states change from gas to liquid to solid
• The second law of thermodynamics states that all spontaneous processes are accompanied by increase in the entropy of the universe
• Thermodynamics Free Energy


  The maximum amount of chemical energy derived from a spontaneous reaction that can be utilized to do work or to drive a nonspontaneous process
• First Law of Thermodynamics


  Energy can be neither created nor destroyed. In other words, the energy of the universe is constant
• Spontaneity


  Processes that occur without outside intervention
• Spontaneous processes may be fast or slow
• Kinetics is concerned with speed, thermodynamics with the initial and final state
• Positional Entropy


  The probability of occurrence of a particular state depends on the number of ways (microstates)
• Entropy changes in the surrounding are primarily determined by heat flow
• Exothermic process

  ∆Ssurr = positive, more disorder in surroundings
• Endothermic process


  ∆Ssurr = negative, less disorder in surroundings