CHEM

• First law of thermodynamics


  The energy within a system is conserved
• Energy can neither be created nor destroyed within an isolated system
• Energy can only be transferred between the system and its surroundings or converted from one form to another
• Total energy of a closed system

  Remains constant over time
• Energy is conserved
• Activation energy


  The minimum amount of energy required for reactant molecules to undergo a chemical transformation and form products
• Initiation of Reaction


  1. Reactant molecules must acquire sufficient energy to overcome the activation energy barrier

  2. This energy can be provided through collision with other molecules, absorption of photons, or thermal energy from the surroundings
• Collision Frequency


  Activation energy influences the likelihood of effective collisions between reactant molecules
• Higher activation energy barriers


  Result in fewer collisions possessing the required energy and orientation to lead to a successful reaction, thus decreasing the reaction rate
• Reactions with lower activation energy barriers


  Tend to proceed more quickly because a larger fraction of collisions between reactant molecules possess sufficient energy to overcome the barrier and proceed to product formation
• Temperature Dependence


  Activation energy affects the temperature dependence of a reaction according to the Arrhenius equation
• Catalysts


  Lower the activation energy of a reaction by providing an alternative reaction pathway with a lower energy barrier
• Catalysts


  Enable reactant molecules to undergo the reaction more readily, leading to an increase in the reaction rate
• Endothermic reaction


  Absorbs heat from the surroundings (feels cold), AH value is positive
• Exothermic reaction


  Releases heat into the surroundings (feels warm), AH value is negative
• Second-order reaction


  Rate of the reaction is proportional to the square of the concentration of one reactant, or the product of the concentrations of two reactants
• First-order reaction


  Rate of the reaction is directly proportional to the concentration of only one reactant
• Enthalpy (H)


  The heat energy exchanged with the surroundings at constant pressure during a chemical reaction
• Zero-order reaction


  Reaction rate is independent of the concentration of the reactants
• Catalyst


  Substance that increases the rate of a chemical reaction by providing an alternative reaction pathway with a lower activation energy
• Effect of a catalyst


  • Lowering Activation Energy
  • Increased Reaction Rate
  • Unchanged Equilibrium Position
  • Reversible Reactions
  • Reusable
• Increasing temperature


  Generally increases the rate of a reaction
• Increasing pressure


  Can increase the rate of reactions involving gas-phase reactants
• Inhibitors


  Decrease the rate of a reaction by interfering with the reaction mechanism
• Intermediates


  Substances formed during the course of a reaction that may enhance or inhibit the rate of the reaction depending on their stability and concentration
• Increasing the concentration of reactants


  Generally increases the rate of a reaction
• Hess's Law


  Enables the calculation of the change in enthalpy (AH) for a reaction by allowing manipulation and combination of known reactions
• Using Hess's Law

  1. Add or subtract the enthalpy changes of the manipulated known reactions to obtain the enthalpy change for the target reaction

  2. Consider the sign of each enthalpy change (positive for endothermic, negative for exothermic)
• How a catalyst affects reaction rate


  • Lowering Activation Energy
  • Facilitating Reaction Steps
  • Increasing Collision Frequency
  • Enhancing Reaction Selectivity
  • Not Consumed in Reaction
• Factors that can influence the rate of a reaction


  • Temperature
  • Concentration
  • Surface area
  • Catalyst
  • Pressure
• Gibbs free energy


  Change in free energy
• The change in free energy delta G is less than zero for a spontaneous process
• The change in free energy delta G is equal to zero at equilibrium for a reversible process
• The change in free energy delta G is greater than zero for a non-spontaneous process
• A natural spontaneous process will occur in such a way to find the lowest possible energy state
• The maximum amount of work that can be obtained from a spontaneous process is equal to the change in free energy
• The minimum work required to drive a non-spontaneous reaction forward is equal to the change in free energy
• Enthalpy change


  Change in heat energy
• Entropy change


  Change in disorder or randomness
• When Delta G is negative, the reaction is spontaneous