Y1 Chemical Equilibrium (P) Flashcards
Go to completion
Reactions that convert 100% of reactants in to products
Reversible
Where both the forward and backward reactions occur at the same time, this means the reaction mixture contains both ‘Reactants’ and ‘Products’
What is required for the equilibrium to be established?
A closed system- no matter gained or lost from the surroundings
When dynamic equilibrium is reached the conc. of reactants and products…?
Remain the same +photo
Dynamic Equilibrium
Substances transition between the reactants and products at equal rates, meaning there is no net change. Reactants and products are formed at such a rate that the concentration of neither changes. (Rates are the same -> and <-
What effect does a catalyst have on the position of equilibrium?
No effect
How does a catalyst affect an equil. reaction?
Reaction reaches equilibrium faster by providing a shorter reaction pathway leading to products being formed faster
Equilibrium can be established from either side of the equation
The equilibium reached will be the same if you start with only the reactants (LHS) or only products (RHS)
If position of equilibrium lies to the LEFT
Recatants predominate
If position of equilibrium lies to the RIGHT
Products predominate
Position of Equilibrium
+photo
Homogeneous Equilibria
All of the reactants and products are in the same state at STANDARD CONDITIONS. ALL SAME STATE
Heterogeneous Equilibria
Not all of the reactants and products are in the same state at STANDARD CONDITIONS. SUBSTANCES IN DIFFERENT STATES
Le Chatelier’s Principle
When conditions are changed within a closed system in a dynamic equilibrium, the position of the equilibrium moves/shift to counteract/oppose this change
How will increasing the conc of A change the Position of dynamic Equilibrium?
A + 2 B <=> C + D deltaH= -250kJmol^-1
More of A will cause an equilibria shift to the right to use more of A
How will an increase in pressure affect the position of equilibia?
A (g) + B (g) <=> C (g)
2 mols on LHS, 1 mol of RHS. To make it more stable an increase in pressure will cause a shift to the RHS.
When the pressure increases the system will shift to oppose the change, moving to the right to form more products.
How does an increase in temp affect the position of equilibria?
A + B <=> C + D deltaH= -ve
The forward reaction is exothermic as deltaH is negative, meaning that it produces heat, so this means that the backwards reaction is endothermic and so heat is taken in to oppose the change and the postiotion shifts to the left.
The Equilibrium Law
aA + bB <=> cC + dD ( where the lower case letters represent no. moles in a homogeneous reaction )
Kc = [C]^c x [D]^d
——————–
[A]^a x [B]^b
Kc = equilibrium constant ( for concentration)
square brackets show conc. in mol dm^-3
The Equilibrium Constant shows…
The set value, provided the temp doesn’t change, which represents what the reactants and products will settle to. ( Unaffected by pressure and catalyst)
Values of Kc
If C+D are large no. moles, Kc will be large
If A+B are large no. moles, Kc will be small
Working out Units for Kc
PCl5 <=> PCl3 + Cl2
Kc= [PCl3] [Cl2] = moldm^-3 x moldm^-3
—————- ——————————–
[PCl5] moldm^-3
= moldm^-3
Working out Units for Kc
N2+3H2 ⇌ 2NH3
Kc= [2NH3]^2 = moldm^-3 x moldm^-3
—————- ——————————–
[N2] [H2]^3 moldm^-3 (x4)
= mol^-2 dm^6
Calculating Kc
If Kc’s calling
Think I REF
Initial moles
Reacting moles
Equilibrium moles
Final Concentration
( for table headers )
Dalton’s Law of partial pressures
The sum of all the partial pressures of the gases in the mixture is equal to the total pressure
Gas A = 10 Pa
Gas B = 5 Pa
Gas A+B= ? Pa
15 Pa
How do gases exert pressure
By colliding with the wall of the container through random brownian motion
What determines the partial pressure of a gas at a given temp and external pressure?
No. of gas molecules per unit volume
Mole Fraction
Mole Fraction = Number of moles of gas A
—————————————–
Total number of moles of gas in mixture
Partial Pressure
Partial Pressure = Moles fraction x total pressure
Homogeneous Gaseous Equilibria
Kp = (pC)^c x (pD)^d
———————- ( you use the partial
(pA)^a x (pB)^b pressure for pC, pD…)
If Kp’s calling
Think I REE
Initial Moles
Reacting Moles
Equilibrium Moles
Equilibrium partial pressure
( for table headers )
