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
