Equilibrium and Thermodynamics (Chem) Flashcards
How can you tell that a reaction favors the products from a Keq equation?
The numerator is greater than the demonimator,thus it will have a large Keq
How can you tell that a reaction favors the reactants from a Keq equation?
The numerator is smaller than the demonimator,thus it will have a small Keq
True or False
You can substitute any concentration into a Keq expression and expect to obtain an equilibrium constant
False
The concentrations used MUST be equilibrium concentrations
Using the equilibrium equation Keq = kforward / kreverse , write the Keq expression for the reverse reaction of a balanced equation of 2X(g) + 4Y(g) ⇌ 3Z (g)
Keq = X2 [Y]4 / [Z]3
where the exponents are derived from the coefficients from the balanced equation
Using the equilibrium equation Keq = kforward / kreverse , write the Keq expression for the of a balanced equation of 2X(g) + 4Y(g) ⇌ 3Z (g)
Keq = [Z]3 / X2 [Y]4
Write the general forumula of the Keq of the reverse reaction
1/Keq
True or False
Keq can be reported in negative values
False
since concentrations are given in units of moles/liter or molarity, it cannot be negative
In the chemical equation SnO2 (s) + 2CO (g) ⇋ Sn (s) + 2 CO2 (g) , what molecules would we exclude from the equilibrium expression and why?
SnO2 and Sn, because they are solids (s)
We do not include pure solids or liquids in equilibrium expressions
link KA equilibrium page
When do we use the reaction quotient (Q) instead of the equilibrium constant Keq?
When we’re uncertain or do not know the equilibrium concentrations
The equation for the reaction quotient is the same as the equation used for Keq, but the concentrations can be from any moment in time, not necessarily at equilibrium. Similarly, the Q expression should not include pure solids, liquids, or solvents
When Q < Keq…
The ratio of products to reactants is lower than it would be in equilibrium
The reaction will proceed forward
pg. 52 of chem book for examples
When Q > Keq…
The ratio of products to reactants is* greater* than it would be in equilibrium
The reaction will proceed in the reverse
pg. 52 of chem book for examples
When Q = Keq…
The reaction is at equilibrium
pg. 52 of chem book for examples
Combustion and neutralization reactions are ____ thermic
Exothermic (-ΔH)
releases heat
Given Le Chatlier’s principle, an increase in temperature has the effect of:
A shift towards products if ΔH > 0, and a shift towards reactants if ΔH < 0
Given Le Chatlier’s principle, an decrease in temperature has the effect of:
A shift towards reactants if ΔH > 0, and a shift towards products if ΔH < 0
True or False
Catalysts increases the rate of both a forward and reverse reactions, causing it to reach equilibrium more quickly
True
Note: this is only before the reaction is already at equilibrium!
True or False
Catalysts change the relative amounts of products and reactants
False
They only change the reaction rates
Explain the equation ΔE = Q -W . Which law of thermodynamics does this correspond to?
Net change in total energy = Heat added - work done
first law of thermodynamics
if the system is being heated, Q is positive, but if heat is being lost from the system Q is negative. When work is being done by the system on its surroundings, W is positive. This is because work done by te system causes the system’s internal energy to decrease. Work done on the system is negative in the above equation. i.e, when work is doneon a system, its internal energy increases since -(-W) is a positive number.
What formula can be used to calculate the necessary quantity of heat to raise the temperature of a material?
q = mcΔT
aka the calorimetry equation
Where:
q = heat required (J)
m = mass of substance present (g)
c = substance’s specific heat (J/g*ºC)
ΔT = temperature change (ºC)
Write the equation for calculating the changes in enthalpy
ΔH = ΔE + PΔV
Where ΔE = change in internal energy of the system
Enthalpy is measured in Joules (J) or kilojoules (kJ)
What is considered “standard conditions” for standard enthalpy/heat of formation?
1 atm and 298 Kelvins
Name the equation
ΔHrxn = ΔHproducts - ΔHreactants
ΔHrxn = ΔH (bonds broken) - ΔH (bonds formed)
Standard Enthalpy of formation
ΔSrxn = ΔSproducts - ΔSreactants
Standrard Entropy
think: second law of thermodynamics
Name the formula
quantifies the amount of usable [free] energy (energy that can do work) in a system; the change in free energy of a system as it goes from some initial state, such as all reactants, to some other, final state, such as all products
measures the spontaneity of a rxn
Gibbs Free Energy
T = temperature (in kelvin)
S = entropy
| H = enthalpy
## Footnote
units: kJ/mol rxn
ΔG°rxn = ΔG°products - ΔG°reactants
Gibbs free energy equation for standard conditions
standard formation of Gibbs free energy
The ΔG of a reaction at equilibrium is…
Zero
because there is no overall change in the system (reactants arent moving to products and vice versa), there is no change in free energy
ΔG°rxn = -RTlnKeq
Gibbs free energy wrt the equilibrium constant
R = gas constant
T = temp in Kelvins
note: ln is natural log; ln of 1 is 0, ln of a number greater than 1 is positive, and the ln of a number less than 1 is negative
ΔGrxn = ΔG°rxn + RTlnQ
can be used to assess a rxn under non-standard conditions
A reaction in which the product ratio is determined by the relative stability of the products
Thermodynamic control
At low temperature, the reaction is under ____ (rate, irreversible conditions) and the major product is that from the fastest reaction.
Kinetic control
pg. 65
the kinetic product forms more quickly/slowly , is less/more thermodynamically favorable, has a lower/higher activation energy, and is favored at low/high temperatures
forms more quickly
less thermodynamically stable
lower activation energy
favord at low temperatures
the thermodynamic product forms more quickly/slowly , is less/more thermodynamically favorable, has a lower/higher activation energy, and is favored at low/high temperatures
forms more slowly
less thermodynamically stable
lower activation energy
favored at low temperatures