U3AOS2: chemical reactions and equilibrium Flashcards
collision theory
reactant particles must collide for chemical reaction to occur w/ correct orientation and sufficient energy, so the bonds between the reactant particles can be broken
features of maxwell-boltzmann distribution
peak=kinetic energy of most of the particles in the sample
area under curve=total no of particles
left=lower avg KE, right=higher
define activation energy
the minimum amount of energy required to generate a chemical reaction by breaking bonds between reactant particles
effect of changing concentration on equilibrium
increasing conc of reactant or product will favour reaction where substance is reactant, so removing substance
if substance = removed, equil. will shift in order to replace it
adding or removing solids/liquids will X change equ = must change CONC
describe la chatelier’s principle
a system in equilibrium has the tendency to partially oppose any disruption to re-establish equilibrium and minimise effects of changes
define rate of reaction
the change in concentration of a reactant or product per unit time // speed of reaction
most common unit = M/s
factors affecting rate of reaction
proportion: temperature, catalyst
frequency: surface area, concentration, pressure of gases
two types of catalysts
homogeneous: same state as reactants and products
heterogeneous: different state to reactants and products
effect of using catalysts on RR
-reduce AE of reaction as particles on the surface distort and disrupt bonds w/in molecule
-providing alternative chemical pathway
-increases proportions of particles w sufficient energy
-increase frequency of successful collision PER UNIT TIME
-increase ROR
effect of changing temp of reactants on ROR
-increase temp = increase kinetic energy of reactant particles
-increase proportion of particles w sufficient energy
-increase frequency of successful collisions PER UNIT TIME
-increase ROR
effect of changing pressure of reactant gases on ROR
-decrease volume = increase pressure
-increase volume = decrease pressure
-increase number of particles per unit volume if volume dec + pressure incr
-increase frequency of collision
-increase freq. of successful collisions PER UNIT TIME
-increase ROR
effect of surface area of solid reactants on ROR
-increase surface area = increased no. of particles that are exposed and available for collision, reduces shielding of inner particles
-increase frequency of collisions
-increase frequency of successful collisions PER UNIT TIME
-increase ROR
effect of changing concentration of solution on ROR
-increase conc of solution
-increase no. of particles per unit volume
-increase frequency of collisions
-increase frequency of successful collisions PER UNIT TIME
-increase ROR
how do you change the pressure of gases?
by changing the volume
adding inert gases = NO EFFECT
terminology for equilibrium
forward reaction is favoured = equilibrium is shifted to the right
reverse reaction is favoured = equilibrium is shifted to the left
what is dynamic equilibrium
-when the rate of the fwd reaction equals the rate of the rev reaction - both processes are occurring simultaneously
-no observable change
-concentration of products and reactants remain constant but x always equal
is dynamic equilibrium a closed or open system?
closed system to prevent reactant or products from escaping or being introduced
effect of changing pressure on equilibrium
increase pressure = always favours reaction that produces fewer moles of gas
decrease pressure = favours reaction that produces more moles of gas
effect of changing temp on equilibrium
increase temp = favour endothermic reaction, where enthalpy change = POS bc system wants to reduce temperature
decrease temp = favour exothermic reaction, where enthalpy change = NEG bc system wants to increase temp
effect of adding catalyst on equilibrium
increase rate of both forward and reverse reactions - equilibrium may be reached more quickly, but not favour one or change position of equilibrium
define haber process
the industrial process of the manufacture of ammonia from hydrogen and nitrogen
compromise positions of the haber process
-at 200 atm, lower pressure than preferred b/c higher pressure = increased energy costs + more exp. equip to maintain high pressure
-400-450 deg celcius, lower temp favours exo reaction but too slow of ROR and decrease eq. yield (maximise yield per day, not cycle)
-uses iron catalyst
what might a temperature MB curve show you?
-at any temp=range of particle speeds
-most particles don’t have very high or low KE
-x normal distribution = positively skewed
-talk about average KE
an increase in temp generally favours a higher ROR, why?
mainly bc reactant particles have more kinetic energy and so collide with more force, meeting the activation energy required
key constant things at equilibrium:
-amount, in mol and mass, of chemical substances remain constant when eq. is reached
-conc of chemical substances remain constant
-total gas pressure is constant
-temperature is constant
concentration curve features
-flat lines indicate that equilibrium has been reached and conc = constant
-initial steepness/gradient = linked to coefficient
-initially [products] = 0
rate graph features
forward reaction is initially the greatest,
reverse reaction has not begun to starts at 0
reach same point when equilibrium first established
Kc = _____
for aA + bB <-> cC + dD
Kc = [C]c [D]d / [A]a [B]b
Kc = is a constant at equilibrium, can only be affected by TEMPERATURE
Kc represents _____
-the measure of the extent of the reaction ie. tells us if there is more fwd or rev reaction
-larger the Kc value, the greater the proportion of the reactants that is converted to products
no info abt ROR
general Kc values
-more than 10^4 = reaction essentially goes to completion, amount of reactants remaining is negligible
-less than 10^-4 = reaction occurs to a negligible extent only, amount of products formed is neg.
-between two, both fwd and rev reactions are occurring to a moderate extent
effect on Kc is equation is reversed
take the reciprocal
effect on Kc is coefficients are doubled
Kc = squared