LESSON 7: Thermochemistry

• Thermal energy comes from a substance whose molecules and atoms are vibrating faster due to a rise in temperature.
• Kinetic energy is the energy of a moving object. As thermal energy comes from moving particles, it is a form of kinetic energy.
• Heat describes the transfer of thermal energy between molecules within a system and is measured in Joules.
• Temperature describes the average kinetic energy of molecules within a material or system and is measured in Celsius (°C), Kelvin(K), Fahrenheit (°F), or Rankine (R).
• An open system can exchange both energy and matter with its surroundings.
• A closed system, on the other hand, can exchange only energy with its surroundings, not matter. 
• An isolated system is one that cannot exchange either matter or energy with its surroundings.
• • In an endothermic process heat is absorbed by the system from the surroundings. The transfer of thermal energy is from the surroundings going into the system.
• • Exothermic process is any process that gives off heat or transfers thermal energy from the system to the surroundings. 
• The Heat of Reaction (also known as Enthalpy of Reaction) is the change in the enthalpy of a chemical reaction that occurs at a constant pressure.
• Thermodynamics


  Branch of physics that deals with the relationship of heat and other forms of energy
• Thermochemistry


  Branch of thermodynamics which studies the energy changes accompanying chemical reactions and physical processes
• Thermal energy


  The energy associated with the random motion of atoms and molecules.
• Temperature


  The measure of the thermal energy.
• Heat


  Transfer of thermal energy from a body of high temperature to a body of low temperature.
• An open system can exchange mass and energy, usually in the form of heat with its surroundings.
• A closed system allows the transfer of energy (heat) but not mass.
• An isolated system does not allow the transfer of either mass or energy.
• Exothermic process


  Process that gives off heat, transfers thermal energy from the system to the surroundings.
• Endothermic process


  any process in which heat has to be supplied to the system from the surroundings.
• 1st Law of Thermodynamics

  energy can be converted from one form to another but cannot be created or destroyed.
• Expansion


  Work done BY THE SYSTEM (-)
• Compression


  Work done ON THE SYSTEM (+)
• Endothermic


  Heat ABSORBED BY THE SYSTEM (+)
• Exothermic


  Heat ABSORBED BY THE SURROUNDINGS (-)
• Enthalpy 


  Known by the letter H, is a thermodynamic quantity used to describe heat changes taking place at constant pressure.
• Enthalpy of a reaction

  the difference between the enthalpies of the products and the enthalpies of the reactants.
• Standard Enthalpy of Formation

  Heat change that accompanies the formation of one mole of a compound.
• Hess' Law


  It states that the change in enthalpy is the same whether the reaction takes place in one step or in a series of steps.
• Heat Capacity


  known as (C), is the amount of heat required to raise the temperature of a given quantity of the substance bye one degree celsius.
• Specific Heat


  Known as (c), the amount of heat required to raise the temperature of one gram of the substance by one degree Celsius.
• Heat of combustion


  The amount of heat liberated when a given amount of substance undergoes combustion.
• Bomb calorimetry


  (constant - volume) It is an isolated system and it measures the heat of combustion by placing a known mass of a compound in a steel container.
• Constant Pressure Calorimetry


  It is used to determine the heat changes for non-combustion reactions such as acid-base, neutralization, heat of fusion, heat of dilution or heat of solution. Also known as coffee cup.