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Reversible reaction
a reaction which can go in either direction depending on the conditions
when you have a reversible reaction in a closed system, a dynamic eqilibrium is reached
Dynamic Equilibrium
in a reversible reaction the rate of forward reaction is equal to rate of backward reaction
Equilibrium
rate of forward reaction=rate of backward reaction
changes occur on a molecular level only
concentration of all reactants and products remains constant, therefore no observable overall change
Conditions; to reach equilibrium, the reaction must be a closed system (all chemicals kept in), therefore rates of reaction equal
Position of Equilibrium
Proportion of products and reactants in an equilibrium mixture
Changed if conditions changed in a way which changes the rate of the forward or backward reactions
can be changed by changing the reaction conditions
Influenced by concentration, temperature and pressure
May result in colour change
Lies to the left = more reactants than products, therefore higher reactant concentration
Lies to the right = more products than reactants, therefore high product concentration
Le Chatelier’s Principle
If a system at equilibrium is subjected to a change then the position of equilibrium to shift to minimise/oppose that change
Effect of concentration change on equilibrium
Increase concentration of a reactant;
position of equilibrium will move so that the conc of this reactant decreases by reacting with other reactants and turning into products
position of equilibrium moves to the right
more products formed
Decreasing the concentration of a reactant;
position of equilibrium will move so that the conc of this reactant increases again
More products will react to replace the reactant that’s been removed
The position of equilibrium moves to the left
Increasing the concentration of a product;
moves to the left as it shifts to decrease the conc of prodycst
more reactancts formed
Effect of temperature on position of equilibrium
If enthalpy change is negative;
Reaction is exothermic
Temperature increase; position of equilibrium moves to the left
If enthalpy change is positive;
reactions is endothermic
Temperature increase; position of equilibrium moves to the right
An increase in temperature moves the position of the equilibrium in the endothermic direction
Effect of a catalyst on position of equilibrium
decreases time it takes to reach equilibrium by lowering the activation energy
increases rate of forward and backward reactions to the same extent
does not affect the position of equilibrium
Equilibrium Constant, Kc
Solids are never included
Not affected by pressure or concentration, only temperature
Use square brackets around formulae (represents conc in moldm^-3)
Units vary. Must state units. Can have not units
Greater value; the further the positions of equilibrium lies to the right
Smaller value; the further the positional of equilibrium lies to the left
Acids
Donors of H+ (aq)
can be described as strong/weak or concentrated/dilute
Bases
acceptors of H+ (aq)
When disolved in water, it is called an alkali. Common ion to all alkalis = hydroxide ion
Strong vs Weak Acid
A strong acid is fully dossociated/ionised in an aqueous solution. The more easily/quicker an acid can donate H+, the stronger the acid
A weak acid is only partially disscoiated in aqueous solution
Concentrated vs Dilute acid
A concentrated acid consists of a large quantity of acid and a small quantity of water
A dilute acid consists if a large quantity of water and a small quantity of acid
Possible to have a dilute solution of a strong acid or a concentrated solution of a weak acid
Monobasic acid
an acid that has 1 replacable hydrogen ion, such as HCl
Produces 1 mole of H+(aq) per 1 mole of acid
Hydrogen ion concentration = the concentration of the acid
Dibasic acid
An acid that has 2 replacable hydrogen ions such as H2SO4
Produces 2 moles of H+(aq) per 1 mole of acid
Hydrogen ion concentration =2x concentration of the acid
Relationship between pH and H+(aq) concentration
acidity of a solution; a measure of the conc of the aqueous hydrogen ion
pH=-log[H+] where [H+] is the conc of H+ in mol dm-3
[H+]=10^-pH
Acid-based titrations