Chem: Reaction Rates and Equilibrium

activated complex

short-lived structure existing when old bonds are broken and new bonds are being formed

energy of activation

represents the energy needed to transform the reactants into an activated complex

kinetics

study of how reactions happen and how fast they occur

reaction rate

the speed with which a reaction takes place

thermodynamics

the study of energy change in chemical reactions

collision theory

in order for molecules to react, they must collide, but collisions do NOT guarantee a reaction

what needs to happen for a reaction to take place

the collisions have enough energy to break bonds and the proper orientation

reaction mechanism

series of steps in a reaction

Reaction intermediate

a species that appears in some steps but not in the reaction; short lived

what affects reaction rate

nature of reactants, temperature, concentration, pressure in gases, catalyst, surface area

what type of bonds in a reactant allow it to react faster?

ionic bonds

temperature and reaction rate

as temp increases, reaction increases; hotter = particles moving faster = more collisions and energy

surface area and reaction rate

as surface area increases, reaction rate increases ONLY in heterogenous reactants

concentration of reactants in reaction rates

an increase in concentration {R} usually increases reaction rate if all reactants are in the same phase

pressure and reaction rate

increase in pressure increases reaction rate

catalyst and reaction rate

catalysts speeds up reaction

inhibitor

slows down rate

lower activation energy means ____ can form ___ more quickly

reactants, products

enthalpy

heat change, lower is more favorable (-H)

entropy

measure of disorder in a system; more disorder means more likely reaction is to occur (+S)

systems tend to go towards ____ energy and _____ randomness

minimum (-H) and maximum (+S)

spontaneous reactions happen if

entropy is positive and enthalpy is negative

Gibbs free energy formula

G = H - (TS) ; used to determine if reaction is spontaneous

using Gibbs free energy formula, what determines if it is spontaneous?

if (G) is negative

which step is the rate-determining step?

the slow step

increasing the ___ in the slow step increases the rate of reaction

concentration

equilibrium

when the rate of the forward reaction equals the rate of the reverse reaction

Mass action expression

used to describe a system undergoing a chemical change; same thing as equilibrium

mass action expression formula

products/reactants (do NOT include solides or liquids)

if K>1 ___ are favored

products

is K<1, ____ are favored

reactants

same mole ratio at equilibrium means ____

they are the same concentration

Le Chatelier’s principle

when a system at equilibrium is stressed, the system shifts to relieve that stress

increase in products side, system shifts ___

left ←

increase in reactants side, system shifts ___

right →

in an endothermic reaction, if we increase the amount of heat (reactant), the system shifts ____

right →

in an exothermic reaction, if we increase the amount of heat (product), the system shifts ____

left ←

increase in pressure shifts the reaction towards ___

lower # of moles of gases

an increase in pressure with shift the reaction

to the right →

catalysts effect on equilibrium

none, just speeds up rate

when a slightly soluble solid is dissolved in a solution, and another soluble salt with a common ion is added, equilibrium ____

shifts left and causes precipitation (any soluble chemical with a common cation or anion)

higher Ksp is ___ soluble

more

Ksp expression

Products