# General Chemistry Ch. 7 – Thermochemistry

 Isolated system
 the system cannot exchange energy (heat and work) or matter with the surroundings; ie an insulated bomb calorimeter
 closed system
 the system can exchange energy (heat and work) but not matter with the surroundings; a steam radiator
 open system
 the system can exchange both energy (heat and work) and matter with the surroundings; ie a pot of water
 first law of thermodynamics
 deltaU = Q – W Where U is the change in internal energy of the system, Q is heat added to the system and W is work done by the system
 isothermal process
 process that keeps temperature constant which in turn means total internal energy of the system is constant; change in U is zero so Q = W (first law of thermodynamics)
 no heat is exchanged between the system and the environment; thus, the thermal energy of the system is constant throughout the process; Q = zero so deltaU = -W
 isobaric process
 pressure is held constant; does not alter the first law of thermodynamics
 isovolumetric process
 also isochoric, no change in volume; if the gas neither expands nor compresses, no work is performed meaning the first law simplifies to deltaU = Q
 What are standard conditions and what are they used for?
 Standard conditions are 25 C, 1 atm pressure and 1 M concentrations. They are used for kinetics, equilibrium and thermodynamics problems
 endothermic process
 the system absorbs heat
 exothermic process
 the system releases heat
 What is heat?
 the transfer of energy from one substance to another as a result of their differences in temperature; represented by Q
 Equation to calculate the heat absorbed or released on a process
 q = mc(deltaT)q is heatm is massc is specific heatdeltaT is change in temperature
 Equation used to calculate the heat of a phase change
 q = mLq is heatm is massL is latent heat which describes the enthalpy of an isothermal process
 enthalpy
 a state function that is equal to the heat transferred in or out of the system at constant pressure
 Hess’s Law
 enthalpy changes of reactions are additive
 entropy
 the measure of the spontaneous dispersal of energy at a specific temperature, represented by ‘S’
 second law of thermodynamics
 energy spontaneously disperses from being localized to becoming spread out if it is not hindered from doing so
 gibbs free energy
 relates the temperature, enthalpy and entropy to determine spontaneity of a reaction
 exergonic
 a reaction that releases energy; spontaneous
 endergonic
 a reaction that absorbs energy; nonspontaneous
 equation that relates free energy and the equilibrium constant and the version used for reactions in progress
 ?Gorxn = -RT ln Keq R is the ideal gas constant T is the temperature in kelvins Keq is the equilibrium constant   ?Grxn = ?Gorxn + RT lnQ =RT ln(Q/Keq) Q is the reaction quotient
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