CHE120 Midterms

• thermodynamics

  the study of the transformations of energy
• first law of thermodynamics

  the internal energy of an isolated system is constant
• experimentally, changes in internal energy or enthalpy may be measured by techniques known collectively as ‘calorimetry’
• thermochemistry

  the study of heat transactions during chemical reactions
• ‘adiabatic’ processes occur without transfer of energy as heat
• work

  the process of achieving motion against an opposing force
• energy

  capacity to do work
• exothermic

  a process that releases energy as heat
• endothermic

  process in which energy is acquired as heat
• heat

  the process of transferring energy as a result of a temperature difference
• work (molecular terms)

  transfer of energy that makes use of organized motion of atoms in the surroundings and heat is the transfer of energy that makes use of their disorderly motion
• internal energy

  total energy of a system; state function
• internal energy increases as the temperature is raised
• equipartition theorem

  used to estimate the contribution to the internal energy of each classically behaving mode of motion
• free expansion (expansion against zero pressure) does no work
• reversible change

  change that can be reversed by an infinitesimal change in a variable
• reversible expansion

  external pressure is matched at every stage to the pressure of the system
• the energy transferred as heat at constant volume is equal to the change in internal energy of the system
• calorimetry

  measurement of heat transactions
• a change in enthalpy is equal to the energy transferred as

  heat at constant pressure
• heat capacity at constant pressure

  equal to the slope of enthalpy with temperature
• energy transferred as heat at constant pressure is equal to the change in enthalpy of a system
• enthalpy changes can be measured in a constant-pressure calorimeter
• thermochemical data

  provide a way of assessing heat output of chem rxns, including thos involved with the combustion of fuels and the consumption of food
• standard enthalpy of transition

  energy transferred as heat at constant pressure in the transition under standard conditions
• standard state

  pure form of a substance at specified temperature at 1 bar
• thermochemical equation


  chemical equation and its associated change in enthalpy
• hess's law

  strandard rxn enthalpy is the sum of values for individual rxns into which overall rxn may be divided
• standard enthalpies of formation

  defined in terms of reference states of elements
• reference state

  most stable state at specified temperature and 1 bar
• standard rxn enthalpy

  difference of the standard enthalpies of formation of products and reactants
• kirchhoff''s law

  express temperature dependence of a rxn enthalpy
• state function

  internal energy; enthalpy
• dU is an exact differential but dw and dq are not
• change in internal energy

  expressed in terms of changes in temperature and volume
• internal pressure

  variation of internal energy with volume at constant temperature
• joule's experiment

  showed that internal pressure of gas is zero
• joule-thomson effect

  change in temperature of gas during isenthalpic expansion
• CHANGE in internal energy with PRESSURE and TEMPERATURE is expressed in terms of the INTERNAL PRESSURE and the HEAT CAPACITY and leads to a general expression for the relation between heat capacities
• adiabatic processes complement isothermal processes, and are used in the discussion of the second law of thermodynamics