1.7 Equilibria + acid Flashcards
Reversible reaction?
one that can go in either direction depending on the conditions
Dynamic equilibrium?
when the forward and reverse reactions occur at the same rate
Go to completion?
where the reactants change completely to form products
Water in CuSO4.5H2O?
water of crystallisation
When Copper sulfate is heated. Water of crystallisation is given off as steam, leaving a white powder called anhydrous Copper (II)
Process is represented by?
CuSO4.5H2O —- CuSO4+5H2O
Haber process?
formation of ammonia from nitrogen and hydrogen is known as a indrustrial process e.g
N2(g) + 3H2(g)—– 2NH3(g)
Equilibrium?
term to denote balance
2 types everyday = static + dynamic equilibrium
Example of dynamic equilibrium?
dissolving an ionic compound in water
when Copper sulphate crystals = added to water, crystals begin to dissolve and solution turns blue
more Copper sulphate added, deeper the blue colour
when no more dissolves and copper sulphate crystals remain in the solution, solution = saturated and the intensity of the blue colour remains constant
This point, the solution = in equilibrium with the undissolved solid
The concentration of the saturated solution remains the same, the copper (II) sulphate is still dissolving but as it does so Copper (II) sulphate is recrystalising from solution at the same rate
Features of equilibrium?
closed system
dynamic at a molecular level
forward and reverse reactions occur at the same rate
macroscopic properties remain constant
Position of equilibrium def?
proportion of products to reactants n an equilibrium mixture
Le Chatelier’s principle?
states that if a system of equilibrium is subjected to a change the equilibrium tends to shift to minimise the effect of the chamge
Effect of concentration change?
dissolving hydrated copper (II) sulphate crystals in water gives a blue solution because the ion (Cu(H2O)6)2+ is formed
when concentrated HCl is added to a solution of Copper(II) sulphate, the equilibrium is established
(Cu(H2O)6)2+ (aq) + 4Cl - (aq) —– (CuCl4)2-(aq) + 6H2O(l)
Adding moer Hcl adds chloride ions so system tries to minimise the effect by decreasing the concentration of chloride ions so position of equilibrium moves to the right, forming more CuCl42- ions, making the solution yellow - green
Effect of pressure change?
pressure virtually has no effect on chemistry of solids and liquids
Pressure of gas depends on number of molecules ina given volume of gas
Greater the number of molecules, the greater the number of collisions per unit time, therefore the greater the pressure of the gas
E.g 2NO2(g)—–N2O4(g)
2 moles on LHS
and 1 mole on RHS
if the total pressure is increased, the equilibrium will shift to minimise the increase
Pressure will decrease if the equilibrium system contains fewer gas molecules
Position of equilibrium moves to the right which increases the yield of N2O4 and colour becomes lighter
Effect of temperature change?
If the delta H value is negative, its exothermic
If delta change is positive, the reaction is endothermic
for example
2NO2(g) —- N2O4(g)
enthalpy = -24
so if negative, forward reaction is exothermic and if the temp is increased, the system will try to minimise this increase
system opposes the change by taking in heat so the position of equilibrium moves in the endothermic direction, so the equilibrium moves to the left
decreasing the yield of NO2 - making the mixture appear brown
Decreasing the temp?
shifts the equilibrium to the right, favouring the exothermic direction, increasing the yield of N2O4 so the mixture appears a lighter colour
Effect of temp change?
An endothermic reaction absorbs heat from the surroundings whereas an exothermic reaction gives out heat to the surroundings
e.g for a reversible reaction the forward reaction is exothermic and the backward reaction is endothermic
Enthalpy change of forward reaction = the same magnitude as but opposite sign to backward reaction
again
2NO2(g) —- N2O4(g)
since enthalpy change = negative forward reaction = exothermic
if temp = increased, the system will try and minimise this increase
System opposes the change by taking in heat so position of equilibrium moves in the endothermic reaction.
Therefore, equilibrium moves to the left, decreasing the yield of N2O4 and increasing the yield of NO2 making mixture brown
Decreasing the temp?
shifts the equilibrium to the right, favouring the endothermic direction, increasing the yield of N2O4 so mixture appears a much lighter colour
Effects of catalysts?
catalysts speed up a chemical reaction by lowering the activation energy of the reaction
In a reversible reaction, a catalyst will increase the rate of the forward and backward reaction but to the same extent. Therefore, a catalyst does not affect the position of equilibrium but equilibrium is reached faster
Equilibrium constant?
equilibrium position chnges when the temp, pressure and concentrations change
equilibrium position may be described by combining the equilibrium concentrations to give a value for an equilibrium constant
given by symbol Kc
General for equilibrium?
aA+bB—–cC+dD
Equation for Kc?
(C)^c (D)^d /
(A)^a (B)^b
products = top line
reactants = bottom line
concentrations = raised to powers
unit of Kc can depend on equilibrium
Value greater than Kc?
more products than reactants in equilibrium mixture
Position of equilibrium lies to the right
greater the value of Kc , the further the equilibrium lies to the right
