Alevel Chemistry - Topic 10 + 11 Flashcards
What is the state of a reaction in dynamic equilibrium? (3)
- The rate of the forward reaction is equal to the rate of the backwards reaction
- The concentration of reactants and products remain constant
- Forward and backwards reaction is still happening continuously
Explain how dynamic equilibrium is established in the reaction:
H2 + I2 -> 2HI
- When the mixture of Hydrogen and Iodine is heated, the gases Start to react.
- With time, the concentration of Hydrogen and Iodine decreases, slowing down the rate of the forwards reaction
- As soon as hydrogen iodide is formed it starts to decompose, and with increased concentration of this product, the rate of the backwards reaction increases.
- Eventually, the rate of the forwards reaction and backwards reaction is equal and the system is in dynamic equilibrium.
What are the two conditions for dynamic equilibrium to be established?
- The reaction must be reversible
- The reaction must be in a closed container
The effect of changing concentration?
- If the concentration of a reactant or product increases, it will favor the forwards or backwards reaction respectively
- This shift the equilibrium position, to counter act the change in concentration
The effect of changing pressure
- This considers the moles in the overall reaction equation
- If there are more moles of reactant then products, the equilibirum will shift to the right
- If there are more moles of products than reactants, the equilibrium will shift to the left
- If the number of moles are the same, there will be no change in the position of the equilibrium
The effect of changing temperature?
When temperature is increased to a system in equilibrium, the equilibrium will shift in the direction of the endothermic reaction.
When temperature is decreased to a system in equilibrium, the equilibrium will shift in the direction of the exothermic reaction.
The effect of adding a catalyst?
- Both the rate of the forwards and backwards reaction will increase
- No shift in the position of the equilibrium, just the speed at which equilibrium is achieved
What the difference between a homogenous and heterogeneous system?
Homogenous systems are ones in which all components are in the same phase
Heterogenous systems are ones where at least two different phases are expected
Phase = (Solid, liquid, gas, aqueous)
What is the equilibrium law equation for homogenous systems?
> > >
- remember square brackets
- Products over reactants
What is the equilibrium law equation for heterogenous systems?
Leave out any solids or liquids out the regular expression
What is the Haber process?
N2 + 3H2 -> 2NH3 (Exothermic)
+ 250 atm
+ 450 degrees Celsius
+ catalyst (Platinum, tungsten but these are expensive, so Iron is used)
What is the contact process?
SO2 + 1/2O2 -> SO3 (Exothermic)
+ Catalyst (Solid vanadium (V) oxide, V2O5)
+ 2 atm pressure
+ 450 degrees Celsius
What is partial pressure?
In a mixture of gases, the partial pressure of a gas is the pressure that the gas would exert on its own, under the same conditions
How to calculate partial pressure/Kp?
*** ONLY GASES
-Find total number of moles
- Find the mole fraction for each of the reactant or products
- partial pressure = Mole fraction x Total gas pressure
Kp= partial pressure for products/partial pressure for reactants
*Mole fraction has no units, so Kp has same units as that in the total gas pressure
What effect Kc and Kp?
ONLY temperature
What is Qc
The reaction quotient. The Kc or Kp not necessarily at the point the reaction is in dynamic equilibrium
What is Le chatelier principle?
When a system is subject to change, (concentration, pressure or temperature) the system will alter to loosen the effect of that change.
