Chapter 15/16 Concepts Flashcards
Distinguish between a spontaneous and non-spontaneous process and provide examples of each
a spontaneous process is one that occurs without any external input to the system, a non-spontaneous process is one where external input is needed for the process to occur
at a temp. greater than 0 C, ice melting is spontaneous; at a temp. lower than 0 C, ice melting is non-spontaneous
Define entropy.
measurement of randomness or disorder in a system
Describe the conditions for standard entropy.
the entropy of 1 mol of a substance in its standard state at 1 atm
List key trends in standard entropy of atoms and molecules.
standard S of gas > standard S of liquid > standard S of solid
for similar molecules, standard S tends to increase with: increasing molar mass, increased # of atoms in formula
Predict the sign of ΔS of a process and use the sign to indicate whether the system has undergone an increase or
decrease in entropy.
entropy is increased when:
moles of products > moles reactants
more complex molecules are broken into smaller, simple molecules
phase change to a more disordered phase (gas > liquid > solid)
generally, dissolving a solute in a solvent
Give in your own words the second law of thermodynamics.
the state of the entire universe’s entropy is always increasing
Determine whether a process is spontaneous given ΔSsurr and ΔS sys.
ΔS universe = ΔS surr + ΔS sys
as long as ΔS universe is positive, a process is spontaneous
Give in your own words the third law of thermodynamics.
the entropy of a pure crystal is 0 at 0 K
the entropy of a system approaches a constant value when its temperature approaches absolute zero
Define Gibbs free energy.
max useful work that can be done by a system on its surroundings in a spontaneous process at constant T and P
Define standard free energy of formation.
free energy change when reactants and products are in their standard states (pure material, 25 C, 1 atm, 1 M of solution)
Define reversible process.
a process in which the system and surroundings are returned to their initial state
Define equilibrium.
forward and reverse reactions of a process occur at equal rates (ratio of reactants to products is constant)
Differentiate between equilibrium constant and reaction quotient. How is the reaction quotient connected to the
equilibrium achievement?
Q is K at non-equilibrium conditions and indicates the direction of reaction to reach equilibrium
Q < K, higher rate in forward direction
Q > K, higher rate in reverse direction
Q = K, forward rate = reverse rate, at equilibrium
Use the equilibrium constant to predict the relative amounts of reactants to products at equilibrium.
K –> infinity, reaction goes to completion
K –> 0, no reaction occurs
K > 1, more products than reactants
K < 1, more reactants than products
Differentiate between heterogeneous and homogeneous equilibria.
homogeneous –> all products/reactants are in the same phase
heterogeneous –> products/reactants in mixed phases, only include gaseous and aqueous materials (include phase in equilibrium expression)
