chem 1b, exam 1 ch 15 and 16

chap 15: chemical kinetics chap 16: chemical equilibrium

reactants —> products

A+B —> C+D

irreversible reactions

only occur in one direction

reactants to products

reversible (spontaneous)

can occur in both directions

rxn @ equilibrium

the rate of the forward reaction is the same as the rate of the reverse reaction

*rate is how fast the reactions occurs

Equilibrium constant K_eq

for aA +m bB —> cC +dD

K_eq = [C^c*D^d]/[A^a*B^b]

*solids and liquids not included

Concentration @ eq

when reaction is at equilibrium the concentration (M) of reactants and products remains unchanged

Rules for K_eq

if K_eq > 1 product favored, goes to the right

if K_eq = 1 neither side of the reaction is favored, equal amounts each side

if K_eq < 1 reactant is favored, goes left

if K_eq > 10¹⁰ reaction goes to completion, no more reactants, irreversible

if K_eq < 10^-10 reaction does not occur

K_p = K_c (RT)^{delta n}

K_c is used when the concentration is given as the molarity (aq solution), K_p is used if the partial pressures are given (gasses)

K_eq relationship

• if a reaction is reversed, K_eq is inverted

• if a reaction is multipliers or divided the same is done to K_eq

• id two or more reactions are added to obtain an overall reaction, multiplu the K≤eq≤ og the individual reactions

Le chateliers principle

if a reaction at equilibrium is disrupted the reaction shifts to the side to cancel the disturbance until the equilibrium is re-established

• adding heat,

  • for exothermic rxn, rxn will shift to the left

  • for endo rxn, rxn will shift right

• adding pressure,

  • the reaction will shift to thew side with fewer number of moles

• adding volume

  • the rxn will shift to the side with higher number of moles

reaction quotient Q

Q is calculated the same as K_c and K_p but the reaction is not at equilibrium

so: [products]/[reactants] not including solids or liquids

reaction quotient Q rules

if Q = K_c neither side is favored

if Q < K_c product favored, shift right

if Q > K_c reactant favored, shifts left

kinetics

the study of the rate of chemical reactions

rate

change in quantity with respect to time

• is how fast reactants make products

• measures how the concentration of reactants change with time

• positive, being produced

• negative, being consumed

factors affecting the rate of a reaction

• temperature, increase in temp increases rate of the reaction

• pressure, increase pressure increases rate of the reaction

• catalyst, catalyst increases the rate of the reaction by lowering the activation energy

• concentration, increasing concentration increases the rate of a reaction (based on its rate law)

• volume, increasing volume decreased the rate of a reaction due to less collisions between the particles

• nature of the reactants, g > l > powdered s > rock s

• surface area, increasing the surface area increases the rate of the reaction

rate law K

*depends on the concentration anbd is always determined experimentally