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General Chemistry Ch. 7 - Thermochemistry
MCAT
22
Chemistry
Undergraduate 1
03/31/2016

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Term
Isolated system
Definition
the system cannot exchange energy (heat and work) or matter with the surroundings; ie an insulated bomb calorimeter
Term
closed system
Definition
the system can exchange energy (heat and work) but not matter with the surroundings; a steam radiator
Term
open system
Definition
the system can exchange both energy (heat and work) and matter with the surroundings; ie a pot of water
Term
first law of thermodynamics
Definition
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
Term
isothermal process
Definition
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)
Term
adiabatic process
Definition
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
Term
isobaric process
Definition
pressure is held constant; does not alter the first law of thermodynamics
Term
isovolumetric process
Definition
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
Term
What are standard conditions and what are they used for?
Definition
Standard conditions are 25 C, 1 atm pressure and 1 M concentrations. They are used for kinetics, equilibrium and thermodynamics problems
Term
endothermic process
Definition
the system absorbs heat
Term
exothermic process
Definition
the system releases heat
Term
What is heat?
Definition
the transfer of energy from one substance to another as a result of their differences in temperature; represented by Q
Term
Equation to calculate the heat absorbed or released on a process
Definition
q = mc(deltaT)
q is heat
m is mass
c is specific heat
deltaT is change in temperature
Term
Equation used to calculate the heat of a phase change
Definition
q = mL
q is heat
m is mass
L is latent heat which describes the enthalpy of an isothermal process
Term
enthalpy
Definition
a state function that is equal to the heat transferred in or out of the system at constant pressure
Term
Hess's Law
Definition
enthalpy changes of reactions are additive
Term
entropy
Definition
the measure of the spontaneous dispersal of energy at a specific temperature, represented by 'S'
Term
second law of thermodynamics
Definition
energy spontaneously disperses from being localized to becoming spread out if it is not hindered from doing so
Term
gibbs free energy
Definition
relates the temperature, enthalpy and entropy to determine spontaneity of a reaction
Term
exergonic
Definition
a reaction that releases energy; spontaneous
Term
endergonic
Definition
a reaction that absorbs energy; nonspontaneous
Term
equation that relates free energy and the equilibrium constant and the version used for reactions in progress
Definition

ΔGorxn = -RT ln Keq

R is the ideal gas constant

T is the temperature in kelvins

Keq is the equilibrium constant

 

ΔGrxn = ΔGorxn + RT lnQ =RT ln(Q/Keq)

Q is the reaction quotient

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