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)
Predict the direction of a reaction given initial concentrations of reactants and products and the value of the equilibrium constant.
very large K –> product conc. very large or reactant conc. very small, reaction will go to completion, equilibrium favors products
very small K –> product conc. very small or reactant conc. very large, reaction proceeds very slowly or no reaction at all, equilibrium favors reactants
Give in your own words the meaning of Le Châtelier’s principle
when stress is applied to a system at equilibrium, the system will shift to reduce applied stress and re-establish equilibrium
Apply Le Châtelier’s principle toward determining the shift of a reaction at equilibrium given a change in one
of the following: removal or addition of reactant or product, change in volume or pressure, and temperature
change.
adding more reactant –> shift towards product
removing product –> shift towards product
adding more product –> shift towards reactant
pressure increased –> equilibrium shifts to produce smaller # moles of gas
pressure decreased –> equilibrium shifts to produce larger # moles of gas
same # moles of gas on both sides –> pressure doesn’t effect equilibrium
volume increased –> equilibrium shifts to produce larger # moles of gas
volume decreased –> equilibrium shifts to produce smaller # moles of gas
same # moles of gas on both sides –> volume doesn’t effect equilibrium
exothermic reaction:
increase T –> K decreases, favors reactants
decrease T –> K increases, favors products
endothermic reaction:
increase T –> K increases, favors products
decrease T –> K decreases, favors reactants
how do catalysts and inhibitors effect equilibrium
neither have an effect on equilibrium when added to a reaction, just effect the speed at which equilibrium is met
manipulating chemical equations
reversing an equation –> invert K (1/K)
multiplying coefficients by n –> raise K to nth power (K^n)
adding equations –> multiply K values (K1 * K2)
