Rate Equation and Constant Flashcards
what is the rate constant (Kc)?
the equilibrium constant
what is the Kc equation?
[products] / [reactants]
what do powers represent in the Kc equation?
the number of moles in the equation
what are the units?
moldm-3 s-1
what is meant a reversible reaction?
reaction goes forwards and backwards
describe the forwards reaction
initially reactants are used up quickly but rate slows as concentration decreases
describe the backwards reaction
initially reactants are reformed slowly but this increases as product concentration increases
what is meant by dynamic equilibrium?
rate of forwards reaction = rate of backwards reaction
- concentrations of each substance remains constant
what is a homogenous Kc reaction?
all reactants and products are in the same state so are all used in the final expression
what is a heterogenous Kc reaction?
reactants and products in different states so solids and liquids not in final expression due to their concentrations remaining constant
state what would happen to the equilibrium composition of a mixture if more reactants are added
- shifts right
- to reduce amount of reactants
- and counteract the change
what would happen to the Kc value if more reactants are added?
nothing
what would happen to the equilibrium position if the concentration of a catalyst increased?
- position isn’t affected
- established more quickly
- because rate of forwards and backwards reactions are equal
what does it tell us if temperature increases and Kc decreases?
- more reactants are reformed
- reaction has shifted left
- forwards reaction is exothermic
when does pressure affect Kc?
when there are more gas molecules on one side
- if pressure increases, shifts towards fewest gas molecules
describe the effect of temperature on Kc
- increasing temperature shifts equilibrium in the endothermic direction
- decreasing temperature shifts equilibrium in the exothermic direction
- if forward reaction is endothermic, Kc increases
- if forward reaction is exothermic, Kc decreases
the student added more reactants to the mixture; what would happen to the equilibrium constant and why?
- shifts right
- form more products
- decrease amount of reactants
what happens to the value of Kc if reactant concentration increases?
nothing
what would happen to the equilibrium position if the concentration of the catalyst increases and why?
- nothing
- equilibrium is established more quickly
- rate of forwards and backwards reaction increases equally
comment on the value of Kc and equilbrium if temperature increases, resulting in more product formation
- reaction shifted right
- forwards = endothermic
- Kc increases
state 2 features of a system in dynamic equilibrium
- backwards rate of reaction = forwards rate of reaction
- concentrations remain constant but are constantly interchanging
what is the effect of pressure on Kc?
nothing
if temperature increased and Kc decreased, what has happened to the equilibrium position?
- shift left
- as backwards = endothermic and forwards = exothermic
- reforms reactants
suggest why methanol is added to petrol
adds oxygen
if pressure increases, explain what happens to the composition of equilibrium
- shifts to side with fewer gas molecules
- increase in the product/reactant of this side
if temperature increases and equilibrium shifts left, explain what has happened to the value of Kc
- decreased
- backwards = endothermic
- so forwards = exothermic
- more reactants are formed
disadvantages of high pressure
- can be dangerous
- expensive
advantages of high pressure
- shifts equilibrium to fewest gas molecules
- if fewer on right, more products form
- more energy and collisions
disadvantages of high temperature in an exothermic reaction
- shifts in endothermic direction
- so more reactants are formed instead of products
advantages of high temperature
- molecules have more kinetic energy
- more collisions
- rate increases
advantages of using a catalyst
- provides alternate reaction pathway
- more molecules exceed activation energy
- reaction can take place at a lower temperature
define rate of reaction
change in concentration over time
