Stoichiometry, Kinetics, and Equilibrium Flashcards
says that the mass of the reactants in a reaction must equal the mass of the products
chemical equations must be balanced so there are the same number of atoms of each element in the products as there are in the reactants
law of conservation of mass
Strategy: Solve for how many grams of a reactant needed to form x number of grams of product
- Determine number of moles of product you want to produce (moles = g / g per mol)
- Set up molar ratio to determine number of moles of reactant you need to react w/ product (based on reaction coefficients)
- convert moles of reactant to grams (grams = moles * molar mass)
reactant that would be used up first if the reaction were allowed to run to completion
not necessarily the reactant of which you have the least
limits the amount of product that can be formed in the reaction
limiting reagent (reactant)
Strategy: Determine limiting reagent
- Balance the equation
- Determine how many moles of each reactant we have: divide the mass of each by its molar mass
- Based on molar coefficients, determine how many moles of one reactant is needed to react with the other reactant; Determine which will be depleted first
actual series of steps through which a chemical reaction occurs
reaction mechanism
a species that is formed for a very short period of time in a chemical reaction but does not appear in the overall net reaction equation
reaction intermediate
step in reaction mechanism that determines the overall reaction rate
slowest step in a proposed mechanism in a rxn mechanism
imposes an upper limit on how fast a reaction can go
rate-determining step
for nearly all forward, irreversible reactions, the rate is proportional to the product of the concentrations of the reactants of the rate determining step
rate law: (forward, irreversible reactions)
Rate Law for general reaction: aA + bB —–> cC + dD
rate = k * [A]^x * [B]^y
Note: k = known constant; x and y = orders of reaction determined experimentally; [A] and [B] = molar concentrations of species A and B (reactants in chemical equation–mol/Liter)
sum of the orders of the reaction (x + y)
sum of exponents in rate law
overall reaction order
If the concentration of one reactant is doubled and the rate of reaction increases by a factor of 2, the reaction is _______ with respect to that reactant. The reactant receives an exponent of ____ in the rate law
first order; 1
if the concentration of one reactant is doubled and the rate of the reaction increases by a factor of 4, the reaction is _______ with respect to that reactant. The reactant receives an exponent of ____ in the rate law
second order; 2
if the concentration of one reactant is doubled and the rate of the reaction does not change, the reaction is _______ with respect to that reactant. The reactant receives an exponent of ____ in the rate law.
zero order; reactant does not appear in reaction rate law
4 Factors that affect the reaction rate
reactant concentration
temperature
solvent
catalysts (enzymes)
The greater the concentration of reactants (more particles per unit volume), the _____ will be the number of effective collisions per unit time, causing the reaction rate to _______.
greater
increase
Reaction rate is _________ proportional to reaction concentration except for _____ reactions, when the reaction rate is not dependent on the concentration of reactants.
directly proportional
zero order reactions
Reaction rate and temperature are __________
directly proportional
As the temperature increases, the reactant molecules have more ______ and Ea will be reached more quickly.
Energy
Catalysts increase the rate of chemical reactions by _____________
lowering the activation energy of the reaction
a dynamic state at which the forward and reverse reaction rates are equal
molar concentrations of the reactants and products are usually not equal
equilibrium
ratio of product to reactant concentrations
pure liquids and solids do not appear in the expression
characteristic of a given system at a given temperature
equilibrium expression (Keq)
Equation: Equilibrium Experssion (Keq)
Rxn: aA + bB —-> cC + dD
Keq = [C]^c * [D]^d / [A]^a * [B]^b
(Rf = Rr)
Note: Raise the concentration of the molecules in the reaction to their stoiciometric coefficients
If the value of Keq is very large compared to 1, then at equilibrium, there will be much more of the _________ than the ______.
more products than reactants
________ and ______ do not appear in the equilibrium constant expression.
Pure solid
liquids
If a stress is applied ot a system at equilibrium, the system will shift in such a way as to relieve the applied stress
Le Chatelier’s Principle
Increasing the concentration of a species will shift the equilib ________ from the species that is added (to use it up)
away from that species
An increase in the pressure of a system will shift the equilibrium so as to _____ the number of moles of gas present
decrease (decrease entropy)
If the temp was increased, the ___________ rxn will shift to the right and the ______ rxn will shift to the left
endothermic shifts to the R
exothermic shifts to the L
If the temp was decreased, the ______ rxn will shift to the left to produce more heat to raise the temp, and the _____ rxn will shift to the right, to produce more heat to raise the temp
endothermic rxn shifts to the L
exothermic rxn shifts to the R
When we add an ionic compound to a water, it usually dissolved by dissociating into its _______
component ions
solution that contains the maximum number of ionic particles before a precipitate forms
saturated solution
when a solution is saturated, a dynamic equilibrium exists between the _______ and the _____.
solute (dissolved substance)
solid
a dynamic equilibrium between dissolved and solid solute
saturated solution
equilibrium constant for dissolution
greater this value, the more soluble the solute in that solvent
solid compounds do not appear in expression bc it is a pure solid
dependent on Temp
solubility product constant (Ksp)
Equation: K(eq) / K(sp)
Rxn: Fe(OH)3 (s) —-> Fe3+(aq) + 3OH- (aq)
Keq = Ksp = [Fe3+][OH-]^3
Note: Concentration of ions are the concentration at saturation level
The higher the Ksp, the _______ it is to reach saturation b/c more compound will dissolve
harder
The solubility product constant (Ksp) is _________ proportional to temperature
directly proportional
solubility increases w/ temperature
maximum number of moles of a compound that will dissolve in 1 L of solution
molar solubility
Molar solubility corresponds to the _________ at that Molarity
concentration of that ion * number of moles of that ion present (stoichiometric coefficient / subscript of molecule)