Reaction Rates And Equilibrium Flashcards
What is the collision theory
For a reaction to occur, particles must collide in the correct orientation and with sufficient kinetic energy to overcome the activation energy
What is activation energy
The minimum energy which particles need to collide to starch a reaction
What is rate of reaction
The rate of reaction measures how fast a reactant is being used up or how fast a product is being formed
Rate =
Change in conc/ time
Y/x on graph
Rate units
Moldm-3 s-1
Factors that affect rate
Conc or pressure
Temperature
Surface area
Catalyst
How does temerature affect reaction rate
HIGHER temp= more particles with higher kinetic energy
More successful collisions per second
Surface area- how does it affect reaction rate
Increased surface area = total number of collisions increased
Greater probability of successful collisions per second
Greater SA:v ratio = more contact
How do pressure /conc affect reaction rate
More particles per unit volume - frequency of collisions increased
Greater number of successful collisions per second
METHODS for following reaction progress
Monitoring change in masss - moss of mass of reactants using a balance( when product is a gas)
Volume of gas given off
What is a catalyst
Increases the rate of reaction by providing an alternate reaction pathway with a Lower Ea
Chemically unchanged
TYPES of catalyst
Homogenous
Heterogenous
Homogenous catalyst
Same psychical state as the reactants
E.g. In an aqueous state - or a reaction between 2 aqueous solutions e.g. Enzyme
- forms an intermediate species- the reactants combine with the catalyst to make an intermediate speciies which then reacts to form the products and reform the catalyst
Heterogenous catalyst
Different phase from the reactant
- e.g. The haber proccess - gases passed over a solid iron catalyst
Reaction happens on the surface of the catalyst , so increasing the SA of the catalyst increases the rate of reaction
E.g. Usually solids wheras reactants are gaseous/solutions
ADSORBED9 weakly bonded, to surface and removed by DESORPTION
WHAT DOES the Boltzmann distribution show
Starts at o,o because there are no molecules that have 0 energy
Most moecluels are original t moderate speed
Some molecules move sat and have high energy
Curve NEVER meets the x aci because there’s no maximum energy for a molecule
Boltzmann distribution - area under the curve
Number of moecluels
Temperature- the Boltzmann dis bitcoin
Peak moves , greater proportion exceed Ea
Catalyst - Boltzmann distribution
Ea reduced
Reversible
Reactions that take place in both the forward and backward directions
Industry and environmental stability - benefits of using catalysts
Iron is used as a catalyst in ammonia production- means temperature design have to be so high( expensibe)
Lower temps+ pressures used- energy saved- less co2 and fossil fuels
Dynamic equilibrium
Forward and backward reaction are occurring at equal rates
The concentration o reactants and products remain CONSTANT
Can only happen in a closed system - no external conditions, isolated from surroundings
As reactants get used up…
Forward reaction slows
As more product is formed - the reverse reaction speeds up
After a while - forward reaction wil be going at same rate as backwards = amounts o products and reactants won’t change
Le chateleirs principle
If an external condition is changed, the equilibrium will shift to oppose the change
If equilibrium moves left…
Get more reactants
SMALLER yield
If equilibrium moves right…
Get more products
GREATER yield
Factors affecting equilibrium
Temperature
Concentration
Pressure
How does temperature affect equilibrium
As temp decreases, the equilibirum will shift in the exothermic direction to product more heat
If temp increases , équilibré will shift in the endothermic direction, to abosrb more heat
How does concentration effect dynamic eulilibium
If you increase reactant concentration, equilibrium shifts right o make more products
If you increase product concentration, equilibrium shifts left to make more reactants
- decrease reactant = shift left to make more reactants
How does pressure affect equilibrium
Gases only
- INREASING pressure shifts equilibirum to side with fewer gas moles to reduce pressure
- decreasing pressure shifts equilibrium to side with more gas molecules to raise pressure
Catalyst - dynamic equilibrium
QwNO EFFECT on equilibirum position
Speed up the forward and reverse reactions by the same amount
Equilibirum is reache faster
