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)
adiabatic process
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 heat
m is mass
c is specific heat
deltaT is change in temperature
Equation used to calculate the heat of a phase change
q = mL
q is heat
m is mass
L is latent heat which describes the enthalpy of an isothermal process
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
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
a reaction that releases energy; spontaneous
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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