Chemical Equilibrium Booklet Flashcards
what does a 0% yeild indicate
no apparent reaction has occurred and almost 100% of reactants are left
what are 2 ways to describe the position of an equilibrium
percent yeild and equilibrium constant (Kc)
what are the conditions necessary for a chemical reaction (3)
particles must collide; the reaction is reversible; rate of reaction depends on temperature, surface are and concentration
whats the approximation rule
when the Concentration of the reactants divided by the Kc value is larger than 1000, you can disregard the change in concentration
whats the percent yeild value in a quantitative/complete reaction
> 99.9%
what does a <50% yeild indicate
reactants are favoured
whats the percent yeild value in a reaction where products are favoured
> 50%
whats the Kc value in a reaction where reactants are favoured
<1
formula to calculate Kc of forward reaction
Kc(foward) = [products]/[reactants]
whats the percent yeild value in a non-spontaneous reaction
0
what does it mean if the Kc<1
the equilibrium favors reactants
how is maximum concentration determined for a percent yeild calculation
using stoichiometry
dynamic equilibrium
when opposing changes occur simultaneously at the same rate; equilibrium is always active
what happens to the concentration of reactants as they react in a foward reaction and how does this affect the rate of the foward reaction
the concentration decreases which causes the reaction rate to decrease
what are the steps for Kc calculations involving an ICE table
1). write out the equilibrium reaction and equilibrium law expression
2). draw an ICE chart
3). substitute given values
4). solve for unknown values (x)
5). solve for equilibrium concentrations and use those to determine Kc if needed
what is percent yeild
yeild of a product measured at equilibrium compared with the maximum possible yeild of product
what happens when Kc is 1
neither reactants or products are favored
whats the Kc value in a reaction where products are favoured
> 1
characteristics of an equilibrium constant value (6)
- depends on the systems temperature
- independent of the reagent concentrations
- not affected by catalyst’s
- not affected by time take to reach equilibrium
- normally stated as a numerical value ignoring any units
- the value is greater the more the system favors the formation of products
what states of chemicals can not be included in a Kc expression and why
solids and liquids because the are assumed to have fixed concentrations
what does a >99.9% percent yeild indicate
quantitative/complete reaction has occurred and there is almost no reactants left
whats another name for a Kc expression
equilibrium law expression
how do you use the equilibrium law expression to determine whether a system is at equilibrium
substitute in the given concentrations to the expression:
- if the value is equal to the given equilibrium constant, the system is at equilibrium
- if the value is larger, there are more products than reactants so the reaction must proceed to the left to reach equilibrium
- if the value is smaller, there are more reactants than products so the reaction must proceed to the right to reach equilibrium
what do you assume about starting product concentrations if they are not given to you
that they equal 0
static equilibrium
when the reaction has completely stopped and there is no movement between the reactants and products within the given reaction
what do you bases your equilibrium law expression/ Kc expression on
based on a balanced equation written in net ionic form ignoring concentrations of pure solid or liquid phases
what does it mean when ‘reactants are favored’
more reactants are present then products
formula to calculate Kc of reverse reaction
Kc(reverse) = 1/Kc(foward) OR Kc(reverse) = [reactants]/[products]
what happens to the concentration of products in a foward reaction and how does this affect the rate of the forward reaction
the concentration increases which causes the reaction rate to increase
what does Kc mean
equilibrium constant
what states of chemicals are included in a Kc expression
(g) and (aq)
formula for percent yeild
% yeild = (equilibrium concentration)/(maximum concentration)
whats the formula for Kc
Kc = ([product1]^mols of product1 x [product2]^mols of product2) / ([reactant1]^mols of reactant1 x [reactant2]^mols of reactant2)
how do you get the Kc value to describe a reverse reaction
use a reciprocal fraction where the formula either becomes 1/(Kc of forward reaction) or (concentration of the reactants)/(concentration of the products)
how is equilibrium concentration determined for a percent yeild calculation
experimentally
whats the percent yeild value in a reaction where reactants are favoured
<50%
what does a >50% yeild indicte`
products are favoured
how do you determine Kc
concentration of the products/concentration of the reactants
what does it mean if the Kc>1
the equilibrium favors products
what does it mean when ‘products are favored’
more products are present than reactants
what are the 4 conditions of a dynamic equilibrium
- the reaction has to be reversible so that the rates of the forward and reverse reactions can eventually become equal
- all observable (macroscopic) properties appear constant
- can only be achieved in a closed system
- the equilibrium can be approached from either direction so that it doesnt matter where you start in the reaction as the end result will always be the same
